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Thread: Roof vs Cruise air

  1. #21
    Join Date
    Jan 2011
    Location
    New Port Richey, Florida
    Posts
    75

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    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.

  2. #22
    Join Date
    Jun 2006
    Location
    Indian Hills
    Posts
    1,129

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    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.
    Jim and Chris
    2001 Featherlite Vogue XLV 2 slide with Rivets-current coach, 1999 shell
    Previous 22 years,
    We have owned every kind of Prevost shell but an H3-40

  3. #23
    Join Date
    Nov 2006
    Location
    Wilsonville, OR 97070
    Posts
    852

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    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

  4. #24
    Join Date
    Jan 2006
    Location
    anytown
    Posts
    8,908

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    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.

  5. #25
    Join Date
    Jan 2006
    Location
    Jasper
    Posts
    3,775

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    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

  6. #26
    Join Date
    Nov 2006
    Location
    thomasville,nc
    Posts
    1,209

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    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.

  7. #27
    Join Date
    Aug 2006
    Location
    Houma, LA
    Posts
    1,783

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    Quote Originally Posted by truk4u View Post
    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?
    Tuga & Karen Gaidry

    2012 Honda Pilot

  8. #28
    Join Date
    Jan 2006
    Location
    anytown
    Posts
    8,908

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    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

  9. #29
    Join Date
    Nov 2006
    Location
    thomasville,nc
    Posts
    1,209

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    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.

  10. #30
    Join Date
    Sep 2010
    Location
    Mt Baldy, CA. and Nashville, TN.
    Posts
    111

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    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

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