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OTR Air Dash Light ?
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Dan,
Check to see if the AC clutch engages. If not check the refrigerant charge.
I’m shooting from the lip because I haven’t looked up the AC system, but I seem to recall low refrigerant pressure disables the AC system.
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Thanks Jon. Still have a day job. Will check clutch engagement next this week. If it does not engage, then the compressor is not running. In this case, do I introduce 134a at the reciever located in the condenser bay or at the compressor?
I had not fired the Detroit since April 1, 2013, about 4.5 months. Just finished installing all new slack adjusters and test drove it for that. The tachometer also quit same time as ac, you suppose there’s any correlation? Just kidding.
Alvie, yes brother Jay is still bussing around. Branson – no, as I am still working, we have immediate family in Springfield , Mo. and go there as often as we want. But I would like to meet the people here that help so much. I will retire 1h14 and will be free at last.
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Look for signs of oil leaking or having leaked from behind the AC compressor pulley and down onto the frame and if you have a clean floor also often visable there.
That leak is caused by the seal having failed due to age and having been allowed to remain unused. (the air conditioner should be cycled frequently even in a climate of little use to maintain the integrity of the seal)
If you see you have a leak, chances are you lost your refrigerant charge sufficiently to allow the built in safeguard to keep the compressor from running.
JIM
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Will do Jim. Thanks for all your past contributions on this subject.
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Dan,
If the problem is lack of a refrigerant then you can introduce liquid at the receiver. The system holds around 24 pounds so if you wish the bulk of that can go into the receiver. But to top it off introduce gas at the suction side of the compressor.
The only way you are going to get a lot of liquid in is if you have vacuumed the system and you are filling it with the vaccuum on the system. As Jim says if the leak is at the compressor seal you might as well fix that first. But if the system still has some pressure and the smudge of dirty oil behind the clutch is not real big you may just want to recharge the system. At one time the compressor seal was under $100 and involved about 2 hours of labor.
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I’m going to buy today one of those 30 pound bottles of 134a. Do I hold it upside down to create a liquid going into the receiver?
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I wouldn’t start throwing freon at it without taking the correct steps. It should be evacuated/vacuumed, charged with nitrogen to check for leaks and then freon added to fill the system with pressures checked by gauges. I watched Prevost do mine and it was quite a process to assure all the working components were functioning properly and the pressures were to spec.
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What he said, unless the system pressures are near where they are to be in which case you are just topping it off. But that doesn’t address the leak.
I cannot answer about liquid vs gas because I have seen cylinders where you turn them upside down for liquid, and I have seen cylinders that have two valves, one for gas, one for liquid and the cylinder sits upright.
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Got the 30 pound tank of 134a today, and a longer charging hose. Turns out the fitting on the low side of the receiver is not compatible with the hose fitting. But it is of course compatible with the charge/service port on the compressor. So I’ll just go that route.
Looked for evidence of a leak behind the compressor pulley and the targets below, and could see clearly that there has never been a leak there. Still need to check pressure in the system.
Ambient temps in northern Illinois are ramping up this week with high humidity, and since my get up and go is inversely correlated, progress will slow.
Next steps: 1) put a guage on the fill port of the compressor to see what pressure is there with the engine off, 2) start engine to determine if ac clutch cycles, and if pressure reading changes, 3) if compressor clutch does not cycle, put a little freon in if pressure reading allows for it, and see if the clutch kicks in. Then will update again, thanks for the help.
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I think that the carrier compressor is only compatible with freon gas and not liquid,it is always safer to only charge with gas,it might take longer but there is not any chance of damaging the compressor.
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Absolutely correct. The only place liquid can be added to the Prevost OTR system is at the receiver.
And for those who need a quick check of the system status and an early indication the refrigerant charge may soon need adjustment is to look at the little red ball in the lower sight glass on the receiver tank. When the system has been running a while and the temperatures stabilized, the red ball in the lower receiver sight glass should be in the middle of the sight glass. If it is sitting on the bottom of the site glass the system may be OK, but all that is known is the charge may be less than ideal.
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Jack – Thanks for the heads up. Based on life experience, I would never have introduced liquid to the compressor.
Jon – What you described with respect to the red ball in the lower site glass on the reciever tank is exactly where I’m at.
88 degrees F today, high humidity.
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If when running that is where the red ball is in the lower sight glass I would start looking for an electrical issue. You can access the information needed off the Prevost site and it will just be a matter of verifying the system has all components working.
I have had two large CB failures relating to the OTR system over the years plus a solenoid (relay) failure. I am sure there are other potential failure points in the system.
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Steps I did in the past 3 hours:
1) Put gauge on compressor low side, gauge read 0 psi, burped the valve on the gauge and there was pressure, perhaps not enough to move the gauge needle.
2) From a 30 pound bottle, charged the low side compressor fill port.
3) After one pound of 134a in, compressor clutch started working, after about five pounds of 134a in, condenser blower and evaporator blower began running.
4) After about 7 pounds of 134a in, and a gauge pressure of 30 psi on the low side of the compressor, it seemed to stop taking in the 134a. And the red ball inside the lower sight glass on the receiver barely got of the bottom.
During this filling procedure, engine was on fast idle, over the road switched to ac, selected max cold at the dash, and turned up the drivers fan.
I let it run for about 2 hours, but it didn’t seem to be taking the 134a in late in the session.Do I need to let it run longer? Since I had good flow and then not, I believe the valves, hoses, and gauge are ok (everything is new but China does not guarantee this stuff). The source tank was new/full, and I could sense its weight.
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Dan,
Since the pressure was zero the entire system needed to be vacuumed prior to introducing refrigerant. If the system had any moisture it had to be removed.
At least you confirmed the issue was related to loss or refrigerant.
If you were to bring this to a competent AC technician he would likely replace the dryer, pull a vacuum on the system, insure the system held the vacuum, perhaps overnight, or conversely would charge the system with nitrogen to leak test. If it passed muster he would recharge the system, probably using liquid at the receiver for the bulk of the required charge, and then using gas for the balance using his gauges to verify pressures based on the ambient temperature.
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