Some comments please on pros and cons of each type.
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Some comments please on pros and cons of each type.
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.
Thanks Jon, 2 questions, how much space is used in the bay or bays and does the condenser draw air from under the coach?
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.
Jim did the cruise airs keep you cool when driving in hot conditions?
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.
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.
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.
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
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.
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.
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?
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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
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.
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?
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
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.
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
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.
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.
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.
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.
I clean my filter through a removable panel in the pantry next to the refrigerator.
The refrigerator stays in place.
JIM
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.
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?
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.
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