Roof vs Cruise air

[Bill1170]

Some comments please on pros and cons of each type.

[Jon Wehrenberg]

That's a topic that has been widely discussed. Do a search to find all the posts on the topic. Each has its pros and cons. Cruise Air is typically quieter and works very well to cool the house when parked. It is a more expensive AC with the condenser mounted in the basement and the evaporator remotely located upstairs. It's shortcoming is when used for cooling when over the road there are times when the heat radiating from the highway does not provide sufficient cooling air for the condenser and the unit shuts down. A lot of buses with Cruise Air also have OTR so it is rarely used for cooling when traveling.

Roof airs may be noisier due to their location. The big advantage to roof airs is they will work well when the coach is in motion because the condensing unit is not picking up heated air radiating off a highway. The units are much less expensive than Cruise Air units and replacing them is easily done because they are readily available at almost any RV dealer. By having roof airs some bay space is freed up for other purposes. It is very rare to find a coach with roof airs equipped with OTR so they are the only source of AC whether in motion or not.

Both types have about the same cooling expressed as 13,000 to 15,000 BTU. Both types will draw about 13 amps when running and the converter decides whether they are run solely via shore or generator power or if they can run through invererters while driving.

The debates which have taken place in the past regarding OTR, Cruise Airs, and roof airs is all but over. As coaches are being outfitted with more than 2 slides OTR is impossible to provide because of the lack of a means for ducting. As more slides are being offered, bay space is being reduced as a result of the need for structural members and this makes the use of basement space for cruise air condenesers less available. Weight distribution also becomes an issue so I predict the days of Cruise Airs in coaches is drawing to an end.

[Bill1170]

Thanks Jon, 2 questions, how much space is used in the bay or bays and does the condenser draw air from under the coach?

[Coloradobus]

All three of our Cruise airs are behind the front bumper on out 40ft Beaver XL. But we also have OTR. Our previous 2 coaches had 4 Cruise airs, NO OTR, two condensors were behind the front bumper, and two were placed mid-body. The space the condensors take up is about the size of a 50 lbs bag of dog food.

[Bill1170]

Jim did the cruise airs keep you cool when driving in hot conditions?

[jack14r]

Dometic does not seem to want to be competitive with the price of cruise airs,just the compressor is over $500,and most roof airs are under $650,a new condenser from AAP is over $2500,but I love the cruise airs as they are very quiet and really cool great.I also think that not cutting holes in the roof is a real plus.I hope that Dometic gets more reasonable on their cruise air units.

[Jerry Winchester]

A couple of thoughts. Our prior two coaches had Cruisair units and aside from the drawbacks Jon mentioned, it was often difficult to find people to work on them until you know where to look. While I liked them for the "white noise" they provided, the air outlets were drafty. In the bedroom, my wife would sleep on the side close to the back wall where the air came out. It would ricochet off the front wall, so she's sweating like a fat chick going thru the time of life with the AC turned down to 68 and I'm freezing my nuts off covered in a blanket. And no, she would not change sides with me.

The roof airs are ducted such that the coach is cool with few cold spots. But you can hear the compressor running when it kicks on. Again, mostly a white noise thing for me, but during football season when I spend more time sitting beside the coach, I don't have the Cruisairs exhausting hot air out the side of the bus on me nor do I have to listen to them run since they were all behind the front bumper. I also didn't have three baffles in front of the front axle to drag off, so there are trade offs.

However, I could have bought 6 or 7 new roof air units for what it cost me to repair the Cruisairs in my '92 over the three years I owned it.

[garyde]

Like Jon said, the cruise airs are only used when stopped since I have OTR which by the way is great. I have four. Two in the Galley area for mid cabin, one in the bedroom, and one in front for the front cabin. Rarely do I run all four, two or three at most. They also can be used for heating as well as cooling.

[Coloradobus]

Bill1170, In our Marathon H3-45, our cruise airs were ducted thru the Prevost provided OTR ductwork, but we didn't have the OTR inner workings of condenser and evaporator, just the ductwork, which was something unusual. IN the early 2000 models H's Marathon did, the OTR ducting was retained and the cool or hot air whatever was needed eminated from the windowsills. It seemed to elininate the cold and hotspots. With the salon cruise air and the galley one on too, we were very cool at 105 degrees around Baker Ca, a few years ago.
Unlike Winchester's air flow issue freezing while the lovely Rae was roasting, ducting the cruise airs thru the OTR tunnels made for even temps, and even quieter operating white noise. This was our favorite set up between the 2 Marathons we owned and the current Beaver XL 40

[Jon Wehrenberg]

Bill, Cruise Airs and the amount of space they occupy (along with the space occupied by OTR) has often sparked debate. A salesman trying to sell a coach with roof airs and no OTR will make claims about how much more bay space is available due to the lack of OTR and Cruise Airs, but while there is a degree of truth the space both occupy is minimal.

My Cruise Airs are located behind the bumper and in the center behind the second bays ahead of the fuel tank. Neither space is prime real estate for storage although some converters use the bumper area for a large storage drawer. The key to determining if the space used is significant is to evaluate 2 coaches side by side and to determine if the converter does provide significantly more storage space that is useable. Like Jack I want minimal roof penetrations and if I absolutely had to have roof airs I would want no less than 4, and maybe five. I have 4 Cruise Airs now, but when combined with OTR I am unlikely to be uncomfortable. I gladly relinquish marginally useable bay space for that purpose. If we lived in the coach full time I might have a different opinion. Maybe.

[Jon Wehrenberg]

Bill, final thought......Unless you are having a coach built to your specifications a discussion of roof airs versus Cruise Airs, OTR versus no OTR is nothing more than an academic exercise. Almost all buyers select coaches based on that eureka moment they have as they step into the coach for the first time. They like the feeling it gives them when they see it for the first time. The balance of the decision making process is mentally justifying the choice.

Unless you are so driven by a set of wants and needs you will buy a coach that "feels" right for you. We lucked out on our first coach because that is how we bought it. We had zero preconceived notions of how we wanted it equipped or what systems were important to us. But when we bought our second (current) coach emotion was not part of the equation. We both felt it was a little over the top with respect to colors and interior decor (we really have learned to enjoy it now however) but as seasoned owners it had some very important features. It had OTR, long range fuel, the Series 60, a private toilet, and some other features we wanted. Since everyone is different nobody on this forum is in a position to define your ideal coach. Nor is anyone in a position to rank the priorities. That is entirely up to you. Where you rank colors or decor on your wish list compared to AC systems is going to depend on your needs. And the only way any of us can determine how we prioritize our needs is to do the best we can at selecting a coach and then hope we got it mostly right.

[Gary Carmichael]

Jon, If the cruise air is ducted thru the OTR duct work would you not have to raise the shades to use it, It looks like on a hot day this would let sun in sort of defeating the purpose?

[Jon Wehrenberg]

Gary,

I don't know the answer to that. Maybe someone who has experience AC systems not ducted through OTR and Cruise Airs ducted through it can address that.

I think there are a number of factors that may make trying to come up with an answer difficult. If the glass is not thermopane I suspect not much heat is getting through so having the shades down, with or without air ducted through the sills would be a benefit. If the shades are down and the windows are not thermopane is the AC coming through the ducts carrying very warm air between the glass and shades into the coach? If the coach has slides on one side no air is ducted through the sills on that side of the coach.

Delivering air through the ducts from Cruise Airs sounds like a superb idea, right up until I try to figure out how the cruise airs in the front bumper area with evaporators located who knows where are going to get air into the bedroom, or even the kitchen area and then how did the converter deal with return air? I don't think our coaches were designed or developed without a lot of consideration to a lot of factors, most of which we canot yet comprehend because we haven't tried to design one.

[Bill1170]

Jerry, we too use our coach to attend football games and much time is spent outside by the coach. Did I understand that you liked the cruise airs better for this and they did not blow hot air beside the bus?

[Jon Wehrenberg]

Cruise Airs have the condensers mounted in the belly of the bus and the hot air exhausted from the condensers typically blows out beneath the bus. Depending on if or how the baffles are pointed you may or may not get the warm air blown on you.

Keep in mind the complaining about warm air blown on his ankles from JDUB is coming from a guy who keeps buying coaches whose generators are located in the front bays and the hot air coming from them is blowing a hurricane of warm air up his skirt. If he had just gone and bought a Liberty the complaining he is doing would not have happened. And as long as I am finding fault with his complaining, it must be a converter thing if his Cruise Airs blew cold air on him inside the coach. A well designed coach would evenly disperse the air flow so it did not create hot or cold spots. That's what you get when you shop for price and not quality.

[gmcbuffalo]

The exchange of air for cruise airs being under the bus can be a problem even when parked. I have been in las Vegas and could not cool the coach down with all three CA's running because the condensers were pulling hot air in to cool the system, this hot air will not cool the system, but causes a Hi Pressure shutdown. The venting and pulling of air from under the coach is a design flaw in my opinion for cruise airs.

[Jon Wehrenberg]

I'm not going to defend the design of the Cruise Airs. But if they are properly charged with R-22 they will function quite well when parked because the bus is shading the ground and if the baffles are correct and in place the hot discharge air is carried away from the cooling intake air. Anyone that has serviced Cruise Airs however will attest as little as an ounce of R-22, one way or another has a disproportionate impact on performance. But when they are working right they are very good.

If you are experiencing problems Greg, the first step should be to make sure the hot air discharge is directed away from the intake otherwise the exhaust air is redirected back through the condenser where it gains more heat and this circular air flow causes shutdown.

[aggies09]

To echo Jerry's comments, if you want to sit outside of your coach at football games with the cruiseairs running it can be a blistering hot experience. Loc and I sat between our buses down at Aggieland one weekend with the cruiseairs blowing out towards us like a furnace. One does not require a furnace in Aggieland in September or any other place in the south for that matter. I think Jon is correct in that the days are numbered for cruiseairs and coaches. Frankly, other than being ugly, I think I would prefer the roofairs.

[joelselman]

Cruise airs are very sensitive to proper charging. My first coach (40' 3 CA) had issues in the Southwest over 95F. My current coach (45' 4 CA) will not cool in dry air over about 100F. The only reason I accepted CA's in my current coach is because I was "sold" and the coach has OTR, which lessens the impact.

Don't really know about roof airs; I was at Mira Loma one day when an owner complained his Marathon with 4 roof airs would not cool???

Incidentally, my first coach cooled well in OK City @105F with high humidity. I've heard of people rigging up misters to blow water on the CA condensers in extreme conditions.

[jack14r]

I dry camp on asphalt in Louisville Kentucky for a week every year and I have found that on the hot days 90-95 degrees I can keep the coach 68-70 but I must raise the coach as high as possible to assist in airflow under the coach.As more slides become more common I wonder when the converters will make 5 AC units as the standard.My coach when I took delivery would not cool very well on a hot day,the cruise airs freon charge MUST be tweaked for max performance.

[Ledo]

I have 3 15K roof airs and have had the roof coated with heat reflective coating from CoachWorx in Clearwater Florida before this summer trip. With the bus not heat soaked I can run two airs on low and the galley on auto, which it will cycle off and on and it has kept the bus very cool thru the hottest of days here on this trip in Texas where temps have hovered around 100 each day. While driving I will use the dash air also like everyone else does no matter what system they have if its hot.

[Coloradobus]

Gary Carmichael. To answer your question about window shades and our former Marathon coach's Cruise airs ducted thru OTR ductwork. The air vent slits on our corian windowsills were iinboard of our silhouette shades. We could keep the blinds closed and the vent slits were exposed to blow the cool air aroundthe coach interior.

[gmcbuffalo]

Jon I have not had my CA tweet. But if the coach gets heat soaked (no OTR) while driving I am in for a misserible time while parked. I have checked the intake and discard vents and they are okay. A year ago I installed an additional 12v electrical fan on the Mid CA that supplies the galley(this is the one that has the most problems with Hi Pressure shutdown. I have yet to be in any heat to see if it will help. I may go with Jim Shoen's misters if I need to, but mine will be manual on and off unlike his automatics. I been told that an AC system is functioning okay if it can drop the temp 20 degrees

[Jon Wehrenberg]

I don't know the procedure Jack used to maximize his CA performance, but if I have to work on mine I will use their published R-22 charge amount as a starting point and using my IR gun to read temps make ever so slight adjustments until I maximize the differential. I have heard all sorts of methods over the years such as setting the charge based on pressures, using the "beer cold" method, charging based on the factory volume, etc. but I think our longer runs of tubing dictate charging based on the maximum temperature differential.

As to cooling the condenser Jim Shoen's method is excellent, but if I remember Steve Bennet has a fan set up that increases air flow across the coils and he has had success with that. I do know the exhaust air from the condenser has to be separated from the intake air. Finally, any bus, no matter what the systems should never be allowed to get heat soaked, not only because it makes the AC systems work hard to get the temps down, but some of the laminates are adversely affected by heat and the damage that can occur can get very expensive to repair.

[truk4u]

I have had 4 buses, 2 with cruiseairs and 2 with roof airs and here's my 2 cents:

Cruiseairs
Pros - Cools well, no roof penetration and quiet
Cons - Expensive repairs, difficult to work on due to location, produces excessive heat in patio area, hi temp shut down while driving when you need it the most, poor access to evaporators for cleaning (Liberty you have to remove the refrigerator) and hard to find service locations.

Roof Airs
Pros - Works in any temp, quiet ducted air, cheap to service and/or replace, low amp usage, easy filter cleaning and can be worked on at any RV shop or mobile AC service facility.
Cons - Roof penetration and roof access

[jack14r]

Jon,I replaced a front CA condensing unit recently and I used a freon scale after vacuum pumping the system for 10+ hours,the CA specs call for 1 LB.5 OZ. of freon,at that quanity the pressures were not even close to the manual,it actually took 2 LB. 2 OZ. to get it to the correct pressures and that also got the low side copper line to the coldest(beer cold).From this example I would trust the CA pressure chart rather than the freon weight that CA specs.

[merle&louise]

I have had 4 buses, 2 with cruiseairs and 2 with roof airs and here's my 2 cents:

Cruiseairs
Pros - Cools well, no roof penetration and quiet
Cons - Expensive repairs, difficult to work on due to location, produces excessive heat in patio area, hi temp shut down while driving when you need it the most, poor access to evaporators for cleaning (Liberty you have to remove the refrigerator) and hard to find service locations.

Roof Airs
Pros - Works in any temp, quiet ducted air, cheap to service and/or replace, low amp usage, easy filter cleaning and can be worked on at any RV shop or mobile AC service facility.
Cons - Roof penetration and roof access

Tom,

About what ambient tempature did the CruiseAir shut down?

Why do they shut down? Is it because of their location in the bus? Could their installation be redesigned so that they wouldn't shut down?

I know you had a 1994 Liberty; what model year did Liberty discontinue intalling the return air filter behind the refrigerator?

[Jon Wehrenberg]

Jack, I know the factory fill specs do not take into consideration the longer runs between the evaporator and condenser so we always need to add more. Have you measured the differential between the air out of the evaporator and the air in? I know these are very fussy and too much of a charge is as bad as too little.

I know the charge is close when I see vigorous foaming in the sight glass. Some bubbling is too little, clear liquid is too much. But I still see the temperature differential as the ultimate factor confirmed by pressures on the high and low side

[jack14r]

Each unit is different,I have a differential electronic thermometer and I have seen as much as 20 degrees and as little 14 degrees in different units.Johnny at AAP is very explicit about how to get max performance out of Cruise Airs and he will tell you that you must get the lowest possible temperature on the suction side at the condenser,I have followed his instructions and it works,he also has told me that if you get the pressures by the chart correct,you will need a little more freon to get the unit to max performance and I have found this to also be true.If I could not measure temperature I would adjust the freon pressures by the chart because I have found that is very close to max performance.The temperature of the suction tube at the condenser is obvious if you are holding it when the freon is just right,again(beer cold)is just right.

[johnklopp]

This has been an interesting discussion. Having never seen a cruse air unit I can only refer to the basics of vapor cycle cooling design and the affects typical conditions have on various components.

Keep in mind that a cruse air unit when designed was intended to be in a boat not a bus. Typical ambient temperatures would seldom exceed 95 degrees F. Most of the units probably had water cooled condensers that lowered the condenser cooling temperature to less than 85 degree F.

The compressor in the cruse air units is a standard off the shelf unit made by one of several manufactures. Little difference exists between compressors of similar capacity as the manufacturers will substitute an equivalent compressor if it has a cost benefit. If the compressor is a horizontal type the opportunity to substitute compressors will be limited. All compressors are rated based on an ARI rating standard that is 130 degrees F. condensing temperature and a 45 degree F. suction temperature.

If the condensing temperature is increased the compressor capacity will be decreased. Most compressors are rated up to a 150 degree F. condensing temperature. Unfortunately at that condition the cooling capacity will typically be reduced by approximately 20%
The condensing temperature is the point when the refrigerant condenses to a liquid in the last few rows of a condenser. A typical condenser design will have a 30 degree F. differential temperature between the air entering the condenser (ambient air) and the condensing temperature. That differential is seldom more than 40 degrees F. The condenser is also responsible for providing 5-10 degrees of sub cooling.

Sub cooing is required to ensure that the condensed refrigerant remains a liquid on its way to the metering device located on the inlet to the condenser. If the installer has used marginally sized liquid lines between the condenser and the evaporator, some of the refrigerant will flash to gas causing bubbles and reducing capacity.

If the installer has used a marginally sized suction line, the pressure drop will reduce the suction temperature at the compressor and reduce capacity.

What can be done to increase capacity?
Increase heat rejection at the condenser
lowering the ambient is not realistically possible.
Increase ambient air flow. Can be done with better fans and ducting.
Increase the size of the condenser. Most condensers can easily have an additional row added.
Increase the efficiency of the condenser. Late model condensers are usually micro channel instead of fin tube. Take a look at the condenser on the front of your car. It has this micro channels between the fins. The micro channels often have 5 or 6 holes or tubes in each section. Without a staggered tube design, the air pressure drop is reduced and the air flow increases with the same fans. Micro channel condensers will typically reject over 20% more heat in the same area.


Reduce or eliminate the critical charge
Increase the size of the liquid line receiver. Add one if the system does not have one. Acts somewhat like the water bellows tanks on our fresh water systems. The system should not be affected by the loss of 5 or 6 ounces of refrigerant

[CAPT MOGUL & Sandy]

Dometic does not seem to want to be competitive with the price of cruise airs,just the compressor is over $500,and most roof airs are under $650,a new condenser from AAP is over $2500,but I love the cruise airs as they are very quiet and really cool great.I also think that not cutting holes in the roof is a real plus.I hope that Dometic gets more reasonable on their cruise air units.

Jack, if you don't mind,,,where did you find the roof air under $650? Ed is searching for one now.
Sandy

[jack14r]

John,you are right that the yacht units are water cooled,and the compressors are off the shelf Tecumseh #AKA8515 EXA they are rated at 15,000 BTU.I would like to find a condensing fan motor that was higher RPM and of course would have to be more HP that would fit in the same space,I think that this would help a lot.I don't think that Dometic really wants to improve the cruise air but just keep it as is and keep manufacturing it.

[garyde]

I am always amazed how much action this topic gets. Its crazy. This could go on to infinity. Lets agree that there is more than one way to cool a bus. Everything after that is just degrees. Pardon the pun.

[Jon Wehrenberg]

Actually this is a good discussion because if we pull out the opinions and personal preferences, this discussion has some excellent technical information such as what John has provided. As a result of the information being provided I suspect anyone with a Cruise Air can provide the information to an AC professional and get their CA performing to the max.

One point John makes suggests strongly the importance of maximizing air flow and it makes me wonder if all CA installations in our coaches have unrestricted air flow to and from the condensers.

[truk4u]

Great post John..

Tuga - When the ambient temps got to 90 and the asphalt is cooking, mine would shut down to over temp. Not sure if Liberty made any changes later in the years, but I believe through 2000, you had to remove the fridge to clean the filter. Maybe an XL2 owner will step in.

[JIM CHALOUPKA]

I clean my filter through a removable panel in the pantry next to the refrigerator.

The refrigerator stays in place.

JIM

[johnklopp]

I believe the cruise air is a generally standard design intended of a specific application, but not a bus.

Taking the personal preferences out of the discussion and looking simply at what can be done to increase performance at minimum cost would be a great POG project.

Unfortunately I have never seen a cruise air condensing unit. I assume it is basically a box with the compressor, condenser coil and condenser fan enclosed. The evaporator unit should not need any modifications.

Increasing the air flow would probably be easy by replacing the fan or the motor or both. Two options exist. The first is the motor speed. Based on a 60Hz power supply to the unit, it must operate at 1800 or 3600 RPM. The motor name tag may show a slightly different speed such as 3450 RPM. This is the rotational speed of the motor rotor, not the rotational speed created by the frequency and the number of poles on the motor stator. The difference is slip and all motors have some to a varying degree. To simply increase the speed by a few hundred RPM is not possible with a standard AC motor.

The next option would be to change the pitch on the condenser fan. I am assuming it is a fan and not a blower. This would result in additional airflow, but the possibility of having and excessive air side pressure drop across the condenser exists limiting the total air flow.
The simplest approach may be to add a second fan on the opposite or side of the condenser coil. A second fan will increase the airflow by providing an increase in the available static pressure. I have no idea of the space available. This may facilitate a better discharge point to keep the hot air away from the patio area.

The best option may be to design a new condenser coil with increased heat transfer. The new condenser in conjunction with increased air flow would stop the cruise air units from cutting out on high pressure and increase cooling capacity by reducing the condensing temperature.

Does anyone have pictures of the condensing unit?
Does anyone have an old cruise air condenser to base design changes on?

The goal would be to develop a condenser with fan that would bolt on to existing mounts possibly with extra brackets. The new condenser could be easily installed by a typical AC technician.

In case you’re wondering, I design vapor cycle systems for military vehicles and aircraft.

[gmcbuffalo]

John I have a CA that I have installed a 12v radiator fan just before the air intake for the condenser. If I run this CA with and without the extra fan on, where is the best place to measure the temps to see if this setup really makes a difference?

[jack14r]

John the fan is a squirrel cage blower design with a 1425 RPM 1/4 HP motor.Greg measure the temperature differential at the evaporator and the ambient at the return inside the bus and then turn on the fan and see if the differential increases.I will take pictures of a unit soon.

[johnklopp]

Greg,

This is a great approach to increasing the condenser heat rejection by increasing air flow.

Take a reading on the inlet and exhaust side of the condenser with the new fan off then repeat with it on.
This will give you an idea of the increased heat rejection with the second fan on. You can also measure the amp draw for the compressor. It should be slightly lower.

Take another set of readings the same time as above measuring the inlet and exhaust side of the evaporator.

If you know what the evaporator air flow is you can calculate the cooling capacity taking into account sensible cooling only and ignoring the latent cooling (moisture removal) Q=1.08 x CFM x differential temperature across the evaporator. The air flow should be listed some ware in the CA documents.

You can also measure the heat rejection of the condenser using the formula above. Multiply the condenser result by 1.4 to compensate for the motor heat and the heat of compression added to the refrigerant since the motor is refrigerant cooled. Estimated factor based on anticipated condensing temperatures.

The above information will help evaluate any modifications made.

John

[merle&louise]

Tom,

Thanks for the reply; it is amazing how hot that asphalt can get.

Jim,

Glad to see that Liberty fixed that little problem. Cleaning AC filters is very important to proper cooling. My 93 Newell AC filter for the middle AC was also difficult to get to. You could remove it easily, but putting it back took a little finess.

[Jerry Winchester]

Jon,

I would submit that yes if I had a Liberty, just the casino chic, whorehouse interior would reject heat such that little or no supplemental cooling would be required. However, since I do football tied up to 50 amp shore power now, the CA heat was fairly difficult neat the front of the coach (near where the awning shade is). With the new awnings - two big ones on the curb side and the roof air, I'm thinking I'll be a little happier.

But my Cruisairs would get the bus well-digger's ass cold, so they were dialed in. If you were sitting still. Had my first run in high temp in the new bus this past weekend. Dash AC and two AC's running off inverter kept it cool, but starting the generator prior to arrival and firing up all four was the ticket.

[Jon Wehrenberg]

I'd like to convince everyone with CA units in some other conversion the simple fix would be to jack up the CAs and slide a Liberty under them but there is more to the issue than that.

I don't think there is a single simple answer although Greg's addition of a second fan to supplement the squirrel cage fan sould like the simplest answer. I still suspect a great deal of the problem (apart from trying to cool a condenser with air heated to very high temperatures radiating from a highway) is the failure of the intake air and the exhaust air from the condensers to be separated. A baffle or some type of separator is required if there is any possibility of drawing hot exhausted air back into the condensing unit. I have a center baffle that absolutely stops that type of circular flow.

If that baffle was missing when I bought my bus I would have never known of it. How do you know it is missing if you have nothing to compare it to? It did not take long to recognize how critical that simple barrier is to successful CA operation. I don't think the designers of the CA or our converters are stupid. I do think the locations are a compromise, but when properly charged, and all baffles are in place the CAs work quite well under all but extreme circumstances such as when driving down the highway in the desert Southwest at 3:00 PM when the ambient temps are in excess of 105, and the blacktop has reached temperatures high enough to frie eggs.

[gmcbuffalo]

John I will get out my IR gun when I get back home. Currently in Germany for three weeks.

[joelselman]

Yup, Jon, that's why the OTR for 3 PM runs. Here's the $1,000,000 ?: Will 4 roof airs properly cool a stationary bus in the sun @120?

[Sid Tuls]

No it will be comfortable but you wont be cold. We spend 2 weeks a year in Parker,Az and I have 4 roof airs. The only time I'am cold is after boating with the grandkids and get burnt to you know what!!---then get into the bus for some peace and quite and then I get chilled. Thought you would like to know.

[joelselman]

Thanks Sid. I kinda figured that. If I ever redo the ceiling, I'll probably change to roof air.

[Jon Wehrenberg]

I may be wrong on this, but I don't think so. Removing or replacing the ceiling on a Liberty will probably entail a little more effort than raising and restoring the Titanic.

[BoaterAl]

We ran 2 airs off the inverters and the dash air in Texas...perfect on the road. While at the lake ran 3 airs all day long and 2 at night. I was very satisfied with the....chill. One of the muggy days the drains looked like I had 3 garden hoses running under the bus.

[Kenneth Brewer]

I may be wrong on this, but I don't think so. Removing or replacing the ceiling on a Liberty will probably entail a little more effort than raising and restoring the Titanic.

I don't think so either.

[phorner]

I may be wrong on this, but I don't think so. Removing or replacing the ceiling on a Liberty will probably entail a little more effort than raising and restoring the Titanic.

Not only would the cost be excessive, but I would fear that the value of a bus (and a Liberty in particular) having the CruiseAir's abandoned, holes cut in the roof and roof airs added would drop to about nil.

I would be extremely reluctant as a buyer to consider a bus with such an extreme modification from what the manufacturer/converter had installed. I would question the safety and reliability of a bus that had been substantially "experimented" with.

Although I strive to maintain our bus in the manner that suits our lifestyle best, I always try to look at any proposed "modification" through the eyes of a prospective buyer. I have yet to stray far from the factory-original systems with the exception primarily in the replacement of audio/video components.

In my opinion, keeping the bus as close to "like new" as I can best preserves its value..... well, as best as the value can be preserved keeping the current market in mind!

[jack14r]

I checked today and the condensing motor is a 1625 RPM 48YZ frame 1/4 horse power,the squirrel cage blower fan is 6 5/16 in diameter and 5 1/8 in length.The motor is rated for 3,0 amps and I verified that the condensing unit fan only pulls 1.2 amps.My question is with a 1750 RPM motor how much would the current increase and would there be any real airflow increase?

[Steve Bennett]

We have 3 CruiseAirs in our 40' Marathon. We changed the motor on the blower to a larger, higher RPM unit (I believe it is 1,800 RPM) we also changed the condenser to a double row unit. The other alterations we made were enlarging the exhaust area on the condensing unit (at the bottom) opening up the area on coach floor, adding the late model Marathon rubber ducts under the coach. Removing the foam insulation around the duct area of the floor. These ducts all face to the drivers side, of the coach. All 3 condensing units are behind the front bumper. We also moved some of the wiring,and coolant hoses so they would not interfere with the air flow. The other change was wiring the blower motor to operate 100% of the time, any time the unit & SMX panel are powered up. We also run the fan on the evaporator side constantly when the unit is on. We recently changed the location of the ducting on the front CruiseAir so it would not recirculate the cool air. We moved the intake to below the front overhead cabinetry, making the area behind the TV a large plenum, and ducted it out at the top of the cabinet on the passenger side. We have also insulated all of the ducting in the coach, and have replaced the screens in the output vents to a less restrictive design. We have only had 1 high pressure shut down since making these changes (a 108 degree ambient with a 20+MPH cross wind at a 5,000 foot elevation heading North on 395). I believe the high density altitude, cross wind airflow, and extremely dry air all contributed to the shut down. We are able to keep the coach 70 degrees inside on 100 degree plus days. Keep in mind this is a non-slide 40' coach, we also keep the blinds down in hot weather to help with insulation.

[johnklopp]

Jack,

A bit rough to calculate the changes based on the available data.

I have used standard design conditions for the missing data. Condenser air flow is estimated at 900 CFM at a .75 inch of water column pressure drop across the coil.

Increasing the motor RPM from 1640 RPM to one with an RPM of 1750 will produce marginal results. My calculations show a new air flow of 960 CFM with a new differential pressure across the coil of 0.9 inches and a new HP of 0.2

Best bet may be to slightly increase the diameter of the blower wheel, currently 6 5/16 diameter keeping the existing motor. The discharge scroll around the blower wheel typically has enough room for a small increase in diameter. My calculations show an increase in CFM to 965 using a blower wheel 6.5 inches in diameter. A further increase in diameter to 6.75 inches will result in 1071 CFM using the existing motor. The motor horse power appears OK based on the current power draw of 1.2 amps with a 3 amp rating.

Keep in mind that the actual CFM has not been measured and neither has the pressure drop across the coil. The bottom line is that more CFM is possible without increasing the motor RPM.

My recommendation would be to add an additional fan or blower on the opposite side of the coil to increase air flow if you only want to make modifications on the air side.

If you want to improve the performance as much as possible, change the condenser coil as recommended earlier.

[GDeen]

One thing I learned with my cruiseairs - I set the galley thermostat lower than the front. In my Marathon, they tend to blow the discharge cold air at each other. If they are set to the same temp, the galley will shut down and the front will blow and blow and do a better job of cooling the mid salon/galley area than it does up front. With the Salon unit running and blowing towards the front, it helps quite a bit in keeping the front cool.

Under theory of staying ahead of the heat, I also drop the front shades immediately when stopping to help keep the sun out of the drivers area which tends to be a big greenhouse....My cruiseairs do a fine job of keeping the coach cool even in very hot weather. Staying ahead of the heat curve though is very important - use side shades and awnings if appropriate.

Of course, since we have the OTR air, there is no need to worry about the cruiseairs working while underway...:cool:

[Kenneth Brewer]

One thing I learned with my cruiseairs - I set the galley thermostat lower than the front. In my Marathon, they tend to blow the discharge cold air at each other. If they are set to the same temp, the galley will shut down and the front will blow and blow and do a better job of cooling the mid salon/galley area than it does up front. With the Salon unit running and blowing towards the front, it helps quite a bit in keeping the front cool.



Should have thought of that, so simple, and really important with an H3. Duh....

While camped for any length of time beyond an evening and night, the outside sunshades over the windshield and driver/codriver windows are imperative, when dealing with daytime temps over 102 or so, besides the awning and inside shades.

[jack14r]

Thanks John,I thought that the flow would not be significant with the higher RPM,I hope the pictures come through.

[jack14r]

John,I have ordered a blower fan that is 6.75X5.625,I will have to modify the cage inlet a little to get it to work but I have 2 extra that i scrounged out of a scrap pile..I cannot measure CFM but I can measure air velocity and motor current,I will install it in my extra unit and report the findings in a week or so.

[Jon Wehrenberg]

This is unlikely to be easy with the 2 CAs in the center behind the 2nd bay in a Liberty, but it would appear a small amount of sheet metal work and a second blower or fan on the air inlet side would be all it takes to increase the air flow in the simplest manner. I don't know if it would be easy to mount a fan or pair of fans much like the electric ones found on certain cars, but that comes to mind.

[jack14r]

In my coach the distance from a panel or something else would restrict an additional fan in 2 of the 4 cruise airs.If I can increase the airflow with just a fan change this exercise might be worthwhile,if not,I have lost little,anyway I always like these type of projects.

[johnklopp]

Jack,
Great photos, I always wondered what the CA units looked like. Lets see, if I go to Home Depot and get a window unit then saw off the evaporator end ......

[phorner]

Just a quick note about the performance of CruiseAir units. We are currently in South Jersey where we are expecting triple digit temperatures over the next several days.

Current stats are:

Outside ambient temp. 96

Heat Index 100

Inverter Bay temp 103

Inside bus temp 70 ............. and dropping!

I don't know how this would compare to a similar bus with 4 roof air units, but I am quite pleased with the performance of my CruiseAir units. Four are running as a test. I could probably stabilize the inside temps in the low 70's with three units running, holding one in reserve in the event of a unit failure or increasing ambient temperature.

IR temp of discharge air from the CruiseAirs range from 55 to 59 degrees.

I'll be looking for a sweatshirt soon :D

But I don't think the campground owner will be happy when he gets the electric bill for our site ......

[jack14r]

I did order a new blower that is 6.75 OD X 5.625 W and I checked 6 places on the condenser before and after installation and the wind speed was increased about 10% the amperage on the motor was 1.5 amps which is 25% higher,this is still far below the 3.0 amps the motor is rated for.The force of the air at the exhaust is obviously much greater.

[johnklopp]

Jack,

Great job and good data with photos. Please add the vendors name were you got the blower wheel and the part number. I'm sure some of our fellow members with CA will be considering your upgrade, approximately how long did it take?

[jack14r]

Thanks John,I purchased it from blowerwheel.com item #06240520-016-s-t-di-ccw-01,the fit is tight so we trimmed the housing a little at a time,the time on the first one was 3 hours but I could do the next one in 1 hour,the problem is you must have the CA on a bench.In a couple of weeks I will install the unit in the bus and report how it works.I have an extra CA condensing unit which made this all possible.

[jack14r]

Can anyone guestimate how much airflow would increase if the rpm was increased from 1625 to 1725,and what horse power would be required?

[phorner]

As a very rough guesstimate, if the CFM of the original blower is known, I would increase it by the percentage change in RPM. However, that does not consider the larger cross sectional area or surface area of the blades.....

[johnklopp]

CFMa = CFMb X (SIZEa / SIZEb)3 X ( RPMa / RPMb)

Hpa = HPb X ( SIZEa / SIZEb )5 X ( RPMa / RPMb)3 X (pa / pb)

[phorner]

John,

Thanks,

That's exactly what I meant.....

[gmcbuffalo]

I check the air temp coming out of the evaporator by putting a refrigerator thermometer to the grill. Before 70 deg F. With the AC on full fan 47 degs, turned on the aux fan 49 degs. So with the bus standing still the fan is a negative help. Maybe it will help while on the road. But I was impressed with the drop in temp.

[flloyd]

I've looked into adding a couple of electric radiator fans to the front of my Liberty. 2 of the CA units are behind the front bumper. The grille behind the bumper lets fresh air into the compartment, except when the air operated shutters are closed. Normally, the shutters are open whenever the coach is parked. This seems like a perfect place to mount a couple of radiator fans and a baffle to pressurize the entire compartment and hence the two CA units inside which both exhaust downward.

There is some debate about the purpose of the front shutters and some folks (e.g. Doug at Excalibur) told me that he routinely rips them out altogether. Liberty told me that they were designed to be closed while the coach was in motion to prevent debris from getting into the compartment, and to relieve a situation whereby hot or cold ram air could come into the passenger compartment around the driver's area.

Still, it looks like it would be pretty easy to mount a pair of 12" radiator fans with a cut-out baffle on the inside, behind the shutter assembly. I measured the area and it's a good fit for a pair of them.

I didn't get to start this project but one thing I did notice was that the sealing boot around the steering rod is torn as the rod exits the compartment. It doesn't look easy to replace and so I might suffer some loss of compartment pressurization there.

Overall it looks like a fairly easy project that I may still try next winter when the weather in Arizona is more suited to performing repairs and mods.

Meanwhile, my number 1 problem with running my 4 CA's is the power consumption. With all four of them turned on, it is a near certainty that the 50A breakers in the park pedestal will trip. My inside ammeters are usually reading about 35-40 Amps each in this mode and so we've learned that 2 CA's are safe, 3 are a maybe, and 4 are impossible unless we're running off the generator.

A good workaround has been to install a small portable fan outside that aims into the breaker box, allowing us to be fairly safe on 3 units in hot weather. It's frustrating.

[Jon Wehrenberg]

Fred,

Power management as you know is required to run all 4 CAs. When I want to beat the heat I use all 4 but turn off the HW tank and make sure I don't use any high amp loads like a coffee maker or the microwave. When all 4 are running and I have some lights on and the TV my current draw is around 32 to 33 amps. I have my inverters set at the lowest charge rate so they are not a factor even if I turn on all the lights. In the morning when it is cool I can make coffee, use the dryer or turn on the HW tank because I only have to run two CAs.

Any 50 amp service should easily handle those amperage loads and if the shore power breaker trips it is likely a bad circuit breaker or the connections are loose.

[Kenneth Brewer]

Fred,

Power management as you know is required to run all 4 CAs. When I want to beat the heat I use all 4 but turn off the HW tank and make sure I don't use any high amp loads like a coffee maker or the microwave. When all 4 are running and I have some lights on and the TV my current draw is around 32 to 33 amps. I have my inverters set at the lowest charge rate so they are not a factor even if I turn on all the lights. In the morning when it is cool I can make coffee, use the dryer or turn on the HW tank because I only have to run two CAs.

Any 50 amp service should easily handle those amperage loads and if the shore power breaker trips it is likely a bad circuit breaker or the connections are loose.

My experience is the same: any good park electrical system/pedestal handled all 4 CAs, even here in Texas, NM. AZ, and even Indio or Phoenix, if the HW heater is up to temp prior, and only one inverter charger is set to low amps (>10) and the other turned off. The microwave, rangetop or curling iron would sometimes trip the pole breaker, and an argument would also occasionally arise when one person forgot or ignored previous instructions.

[gmcbuffalo]

Fred why try to pressurize the compartment why not just put the fans blowing into the each CA units compressor coils?

[GDeen]

Fred,
-
Why are you not using the OTR on that bus? Screw cruiseairs for cooling while in motion....fire that big boy up! We were in hours of 106° F + on our first day of this trip, and the coach interior was comfortable in the high 60's running the bus air.

[flloyd]

Fred,
-
Why are you not using the OTR on that bus? Screw cruiseairs for cooling while in motion....fire that big boy up! We were in hours of 106° F + on our first day of this trip, and the coach interior was comfortable in the high 60's running the bus air.

Oh yes, I do use OTR whenever possible, or when I need to hang beef. My discussion here is only about park operations.

[flloyd]

Fred why try to pressurize the compartment why not just put the fans blowing into the each CA units compressor coils?

It's an ease of installation issue. I don't really want to pull the compressor units, and there's not much room to work down there.

[flloyd]

My experience is the same: any good park electrical system/pedestal handled all 4 CAs, even here in Texas, NM. AZ, and even Indio or Phoenix, if the HW heater is up to temp prior, and only one inverter charger is set to low amps (>10) and the other turned off. The microwave, rangetop or curling iron would sometimes trip the pole breaker, and an argument would also occasionally arise when one person forgot or ignored previous instructions.

Speaking of which, I swear that my wife's hair dryer draws more current than a single CA! It's about 1500W

[Jon Wehrenberg]

That's where power managment comes into play. She has the power to decide when she will use her hair dryer and you have to manage the circuit breakers so the shore power doesn't trip.

[Jerry Winchester]

If I over amp at a park, 90% of the time it can be traced to a hair dryer or flat iron. A hair dryer must be akin to a dead short.

[GDeen]

If I over amp at a park, 90% of the time it can be traced to a hair dryer or flat iron. A hair dryer must be akin to a dead short.

A hair dryer is akin to a load tester...

[garyde]

In the on going process of conserving energy, reducing emissions, preventing new oil drilling and building nuclear power plants,
California has outlawed hair dryers. All Californians are now required to have their hair cut to a length no longer than 2 inches.
Hair dryers are being confiscated in mass.

[Jon Wehrenberg]

I see the problem is being addressed across the country. To save the energy consumed in the manufacture of thinking caps, all Tennesseeans are being asked to stop using brain power as is evident by how they drive.

Unfortunately not as much power is saved as was once thought because apparently Tennesseeans have not been using their brains for a long time. We know this to be a fact because it has been documented that the last words uttered by a lot of now deceased Tennesseans have been "Watch this!"

It was thought a lot of power could be saved by eliminating the use of power tooth brushes until someone realized the highest compliment anyone could pay to a Tennessee bride is "Nice tooth."

[jack14r]

This past week I had a cruise air that started hard so I decided to replace it with the modified fan version,the one that needed replacing is the mid port so I checked the differential with a differential tester and it was 16.5 degrees,I then replaced it and checked the differential and it was 18.3 degrees,I was amazed with the amount of water that dripped from the evaporator.

[johnklopp]

Jack,

If you want to donate the old CA unit to be a test mule, I will design and install a new condenser coil with additional capacity. If you’re Interested and coming to POG 10 bring the old one with you. The unit will be returned as soon as I am done playing with it.

[jack14r]

I am not coming to POG 10 but I have an extra one that I would like to donate,I need to put a new compressor in it and change the fan wheel,I guess the condenser should be done first,this would be an exciting project.My starboard unit has never performed as well as the other 3,that would be the one I would like to replace next.I will ship it prepaid,just PM me with the address.