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OTR/Drivers Air issues
After finding and fixing 6 refrigerant leaks (I charged with nitrogen and inspected with Nu-Blue… awesome stuff), I vacuumed the system with all 4 valves back-seated. Then I added 24 lb of refrigerant through the top port of the receiver tank as described in the maintenance manual. I weighed the tank while transferring refrigerant with my Robinair machine. I then backed out the top receiver valve (now all 4 in normal backseated position).
The A/C blows cold at the dash and throughout the coach, but there are a few issues…
1.) The refrigerant level is half way up the TOP sight glass of the receiver tank while operating. The manual says it should be half way up the bottom glass. This one has me really puzzled because I know there are 24 lb 0.2 oz of R134a in the system, the AC blows cold, and there was a vacuum in the system to start with. Admittedly, I haven’t put gauges on the compressor yet.
2.) The AC failure dash light came on after climbing a grade at sustained high RPM (climbing 322 towards 99 near State College PA). I turned the system off right away when the light came on. Otherwise it stayed off for our trip. I’m sure this was the high pressure switch (275 PSI cutout). Probably has something to do with #1, or perhaps you are supposed to turn off A/C in those situations?
3.) 3-4 times, out of the blue, the dash started blowing hot air while the rest of the coach was still cold. I removed the dash panel and expansion valve was still cold. I’m thinking this is the heat overpowering the A/C. Maybe a bad heater solenoid valve in the steer bay. It’s hard to test because it’s so infrequent. Could be a bad temperature rheostat on the console, although moving it around and back to cold doesn’t help. Each time, I was able to get dash A/C going again by turning the heat/AC switch off and back on (while pulled over to check everything over and troubleshoot).
4.) With the dash fan speed all the way down, you can feel the knob click into place over a detent. This tells me the fan should turn off, however it doesn’t. With the heat/AC switch turned off and both fan speed knobs all the way down, as soon as you turn on the ignition you get maybe 25% fan speed and it blows out of the dash vents.
5.) I ordered a filter dryer from Prevost over the phone when I ordered the suction manifold. The dryer in the coach has one inlet and tees into the line coming out of the receiver. The one I received from Prevost has an inlet and an outlet, which is what is shown in the parts diagram. I guess I need to cut a section and the tee out of the line to install this part? Or did I get the wrong part?
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15 Replies
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1999 XLV X-6872, liberty #440 -
Dash air and coach air on an OTR coach is the same system.
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There is a electric solenoid under front right behind front bumper on top for the antifreeze for heat and mine was blowing hot air because solenoid was not holding??
1999 XLV X-6872, liberty #440 -
Dash and OTR share the compressor, condenser, receiver, and dryer. They have separate expansion valves and evaporators.
I suspect that heater valve behind the bumper as well. My only reservation is that it appears it can be controlled from the drivers fan blower controller. Between that and the fact that the fan never turns off all the way has me wondering if it’s an electrical issue. Maybe I can rig up some sort of light to monitor the voltage sent to that solenoid valve.
Any ideas as to why my refrigerant level would show so high in the receiver?
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#2 – Probably a low pressure switch limit being made, not high.
Read this: /threaddetails.asp?Category=HVAC&ThreadID=8180
#5 – here’s my filter drier setup and experience:
/threaddetails.asp?Category=HVAC&ThreadID=11039
email me, donjetman@aol.com, your ph# if you want to talk
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#3 – yes could be bad dash off/on/speed rheostat (lower left in my pic here). Ours has a detent (full ccw) that turns the dash fan completely off and closes the dash freon solenoid valve. Turning it cw opens freon valve for dash circuit and turn on the dash fan, faster as its turned further cw.
and/or bad temp rheostat (lower row center) and/or heat solenoid valve if there is one?. I haven’t looked in a long long time.
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I have the exact same problem with the fan rheostat – not turning off fully. What is the best way to test it? Is there anyway to clean/repair or just replace?
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It might not be the switch it might be the control box for the switch, My friend had that problem and his ran full blast, he replaced the switch and no change. I read some stuff about this controller and it it pricey and it said if you good with electrial you could fix it yourself ??
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Thanks Art,
if you have any links to info please pass them along. My google searches did not result in any good information yet.
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This I think is correct part # in picture ask Prevost,My friend said it was not cheap,I don’t think he bought it yet, He did put in new switch no change
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I ran the bus for about 20 minutes yesterday morning at high idle with OTR on. The refrigerant in the receiver tank was floating the top ball. The high side pressure was 210 and the low side was 35 psi. The hoses before and after the filter/dryer were hot and felt similar in temperature (I don’t have an IR temp gun yet.)
I guess the next step is to start removing the evap fans from the other side and get to the expansion valve to measure temperatures? Does the heater core have to come out too?
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210 psi on the high side seams HIGH to me. As I recall 35/140 is what I see on mine.
If 1 or more of your 2 unloader valves is NOT “unloading” I think the high psi and high liquid in receiver will be the result.With system running you should be able to feel with your hand (or IR temp gun) a big temperature difference from one side of the head to the other when the unloader is unloading (read the manual, I’m going from memory).Maybe I’ll fire my bus up today and get some #s for ya? -
My Prevost (unit# S-5665) mx manual, sec.22, p.402 of 466, high discharge pressure, states the following as possible causes:
1) air or non-condensable gases in the condenser; 2) overcharge; 3) dirty condenser; 4) insufficient cooling air over the condenser.In case your high is too high? -
I went out to the bus/car port and ran the OTR ac for 15 mins with my HF ac gauges and IR temp gun.
OAT was 90*f & high humidity. Inside bus temp was mid 80s.
Static system pressure was 100 psi. Refigerant Pressure Temperature Chart said it should be 104 psi. close enough
Started engine, set HI IDLE. 10 mins after turning on the OTR, both cabin and cockpit, low side was 30 psi and high side was 215 psi. 50*f air was blowing from all vent inside the bus.
Coldest part of the brass area of the low pressure service valve was 54*f. Hottest part of the brass area of the high pressure service valve area was 160*f.
Opened the condenser door several times and all times the ball in the lower sight glass was at the top, and the upper ball was on the bottom. Filter felt equally warm to the touch at both ends.
Both heads with unloader valves were hot to the touch on top, and not so hot to the touch on the bottom.
After 15 min gauge pressure were 28/210.
I hope this helps?
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
Thanks Don, I appreciate you checking that out for me. I’ll check my temps out with a thermocouple on a borrowed Fluke. Our pressures seem very comparable though. The ambient was in the mid eighties when I got 210/35. It cools just fine, the only problem seems to be the high level in the receiver. I’ll check the static pressure as well.
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