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Dash Air Not Cooling
The fan gearbox, A/C Compressor, fan clutch and all belts were replaced last October. The dash A/C would freeze you out. The A/C quit cooling a few days ago. The A/C compressor clutch is not engaging. I am looking for CB72 that my schematic says powers the compressor clutch across contacts on R36. However, the list on the engine compartment door says R86 is the clutch relay. Perhaps there was some changes made during the conversion.
Anyhow, I can not find CB72. Also, the receptacle for R86 is empty. I thought I should at least look for a tripped breaker or fuse before making another trip to Prevost.
I’d appreciate someone pointing me in the right direction to find CB72 or advise on anything else to check.
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31 Replies
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Typically low refrigerant pressure opens the circuit that powers the compressor clutch or compressor. I would put the gauges on the system before spending too much time chasing a problem that might not exist.
Any AC shop can check pressures, or with what Harbor Freight charges for a set of gauges it might be cheaper to just buy your own. I have my own and with all the places I have AC or refrigeration now they are worth their weight in gold.
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Thanks Jon, Tela kept telling me to check the refrigerant but I wouldn’t listen to her…….
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You can bypass the low pressure switch Chuck just to see if the compressor kicks on. If you had an H I could tell you where it’s located, not sure on the XLII.
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Thanks Tom, I did find the CB72 and R36. They were right where Prevost said they were on the door schematic.I just overlooked them. Both are good, so I suspect Jon is correct that the clutch is not engaging due to refigerant low pressure. R85 is for full air systems and R35 is for driver’s air systems. The compressor should still be under warranty. This didn’t act like a slow coolant leak as one day it was ice cold and the next day it wouldn’t cool. Maybe a big leak or a bad compressor.
Last October I paid $1692 at Prevost Ft Worth to have a new York compressor installed as the original one was leaking oil. I replaced the same compressor on my former Wanderlodge LXi for $395…. Crazy? I reckon!
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A low refrigerant prior to crapping out often will do OK, but the evaporator on one with low coolant is prone to icing up. If the fan speed and maybe low humidity were just right it might seem to be working OK just before the freon level reaches the point where it won’t work.
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Ouch, those compressors are cheap, you paid dearly for that one. I get them at Fleet Pride for less than 300 bucks.
Just one other thought. Some have like a 3 minute delay circuit board that keeps the compressor for coming on immediately on start up. I had a problem with one of those, don’t remember which bus, and it failed not allowing the compressor to start. I don’t think my Marathon has that, seems to come on as soon as the button is pushed.
Is the little button lighting up when you push for the compressor at the control?
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Yeah, I did protest the repair cost but ending up paying up anyway. A couple of jobs I have had done at Prevost Ft Worth were far more costly than I thought they should be. For example, I had the slide manifold replaced as the slide seal would not inflate. The tech spent 8 hours trying to get the new manifold to sequence properly. Turns out the new slide manifold’s internal wiring was mis-wired from the factory. Once they discovered the problem and rewired the connector pins on the manifold pigtail, it took 30 minutes to install it and get the slide functioning properly. You gotta know, they charged me $1000 for the 8 hours the tech spent trying to get their mis-wired manifold to work. If it sounds like I’m complaining, I am…. But where else could I go to get a new slide manifold?
Tom, no delays on my A/C’s start up either but the dash air schematic for my coach does show two 45 second delay modules, probably for the head pressure protection.
No, the little green LED does not light up when the A/C button is pressed. The damper opens and the engine fan goes to fast rpms but no green LED. Jon is probably correct that it’s low on R134. If so, it’s got a leak somewhere as it was filled not that long ago. I really try not to use the dash air much but use the roof A/Cs as much as I can. But sometimes they need a little assist in 100* temperatures. My mileage decreases quite a bit running with the dash air on.
I spoke with Rebecca at Prevost Mira Loma who said the A/C is still under warranty (one year) and she could fix it Thursday, so I’m just going to run it over there and let them fix it. A short trip of just 200 miles and maybe, just maybe I won’t have to pay up this time. I have spent a lot of money zeroing this bus out but I did buy it at a very fair price knowing it needed some money spent on it to get it in proper shape. I had both Marathon and Prevost do a detailed pre-purchase inspection on it before I bought it. It’s hard to find a 14 year old bus for sale tha doesn’t need some money spent on it to bring it to proper condition.
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It may be an electrical issue at the switch Chuck. My switch always lights up even if the compressor is out of action. I had issues with the low and high pressure switches just a few months ago that Jeff helped me with and the compressor button light was always lit.
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Jon, you mention having your own gauges. I do as well, although mine are cheaper ones I use on the cars and other small toys to keep the AC in top cooling shape. Since my coach only has dash air is it possible to check the pressures and add refrigerant myself, or is adding refrigerant something better left to Prevost to handle. Wasn’t sure if the dash air is as simple, or close to, as your typical automotive setup. Thanks in advance.
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If you have your own gauges you can charge your own system easily. Sam’s Club has 30 pound tanks of 134A cheap and as long as you don’t let the system pressure get to zero you can nurse it along even if it has minor leaks. Best to stop the leaks however.
I don’t have my charts in front of me, but if you have 45 PSI and 150 (maybe higher) on the high side you will have a system that works well.
Jeff? Do you know the right pressures for an ambient around 85?
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I used to do my own and then decided to let Jeff do it. There’s more to it than just adding freon and Jeff really understands what’s needed. He’s never just added freon to mine, it’s always been vacuumed, nitrogen tested, new dryer then recharged. I will still do my cars, but not the bus.
I watched a service truck guy at Sevierville attempt to just add freon to an H with dash air and the guy with the bus left with no air as opposed to having just some air when he got there.
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If you try to add freon to a car or whatever, be sure to purge the line from the tank to the port so air doesn’t get in. Don’t forget oil too.
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Check to make sure dash HEAT is off. On my old coach, a broken in-line fuse holder caused coolant heat valve to stay open which acted like I had no a/c.
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Thanks for all the replies. My dash air definitely cools, just nor as efficiently as it did several months ago. I noticed it occasionally freezing up in certain conditions, but never failing to cool to my liking, which is akin to a thin layer of ice on the front windows 😉 Well now in temps in the upper 90’s she just won’t cool as well as she used to. So I’m thinking she just needs to be topped off, which in a car is easier than checking the tire pressure haha. But in the coach just wasn’t sure if it was the same procedure.
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Usually icing is associated with low refrigerant or a low fan speed.
2005 XL Thompson Coach
Rarely tow anything behind us.
Sold: 1993 Liberty that we loved for 12 years.
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