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Prevost OTR issues
I live in the Austin, TX area. I am having Prevost OTR issues. And need to find a shop that can add 134a to this system as it appears low. Does anyone have a suggestion, or do I need to go to Dallas/Houston?
The rundown: It all started because I felt the dash ac is not putting out enough cooling. So I opened the cargo door and looked at the dryer and the wet label is showing blue, but it appears I am low on 134a as I see lots of bubbles in the mix. If I look at the recovery tank below the dryer (while AC is running), both the red balls (one at the top and bottom of tank) are resting on the floor of the sight glass and I see no liquid in the sight glasses. The fans are cycling on the condenser like every 30 seconds or so, but the inside temp is still quite a bit above the setting on the dash control. At one point the fans where turning on and off almost like a short, in rapid succession and intermittently. I did not think to go look at the Ac comm. panel on the driver side behind the rear wheels during all this (still new to Prevost, just bought it in late spring), I will do that next time I am out at the shop.
The following readings where taken with an outside temp 80f, bus shaded (been in the shop and moved outside for this test), engine temp ~190f and @ fast idle during test, using a Fluke multimeter with thermal probe to take measurements:
Coach Ac:
Inlet measured at the front stairwell intake: 66f
Outlet measured at the vent right behind the driver side kitchen sink which is as close as I can get to the evap. coil (without opening the bay door and inserting the probe in the evap. bay): 46f (20f delta, this seems ok, but with this huge unit would seem it should be a little more)
Dash Ac (the problem child that started me looking into this):
Inlet measured at the base of the right dash near the stepwell: 66f
Outlet measured at the driver, passenger and defroster: 58f (8f delta, this no bueno)
Also on a similar note, the defroster output can never be shut off. When I pulled the CD Changer/GPS in the stepwell area coming into the bus to look into this, it appears there is no dampner door mechinism to shutoff the defroster, and that it will always be on. I’m I right, or is there one somewhere that I need to track down and repair?
Edited 9/25/13-15:30 hrs:
Forgot to state that I had both units in re-circulate. I verified the coach was not recirculating by checking the side inlet between the 3rd and 4th bay on the drivers side was not taking in air, which it was not. I am not sure where to check the air recirc for the dash air yet.
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11 Replies
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I’m no OTR expert and I didn’t sleep at a Holiday Inn last night, but I do know that on my coach the bottom of the 2 red balls is in the center of the glass when the OTR is properly charged and operating at fast idle with hot ambient temps. I add R-134a to mine each spring as I have a slow leak somewhere. Can’t address your other questions and I would take a look at the compressor oil level through the sight glass just because.
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The compressor oil was in the middle of the sight glass on both sides of the compressor, so good to go there.
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Michael,
Joel gave you the correct answer.
The system can be charged by anyone with refrigeration knowledge. It sounds like your system still has refrigerant so other than someone adding 134 (gas via the suction side of the compressor) you will be good to go.
Look behind the clutch on your compressor. If it is wet with oil that is the likely and most common leak point. If so that entails about $100 in parts and a couple of hours. Look for either Prevost or Carrier Transicold dealers because trailer refrigerator systems use the same compressors and similar parts to service the OTR.
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Jon,
Thanks for the reply. I believe I will purchase R134a and do it myself. Once upon a time I was an ASE Cert. Mech, but moved into the software development field to get rid of the dirty finger nails :). I will need to get the correct adapters for that compressor to fit, and then read up on the Prevost OTR manual on valve position and such so I can charge it.
Being the coach frame was built in 1999 it is in need of some freon, and I dont have the records from the prior owner so have no idea if they ever had it serviced or not.
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The compressor takes standard R-134a fittings.
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In the past month I went through an evacuate and recharge procedure. Some tips:
1) The low side and high side valves on the compressor take a 3/8″ open end wrench.
2) You might index the valve stud with a spot of paint so you can count the 360 degree turns easier.
3) Only turn the valve shaft 3 to 4 turns clockwise to open so it is in the middle of its travel range.
4) Best internet price I found was 80 bucks for the 30 pound bottle. System capacity is 25.
5) Since mine leaked, I put some yellow leak detector in the system with the recharge. It discovered the leak at the low side fill port on the ocmpressor.
6) R134a leaves less oily residue to help discovery than the r12 did. Not saying it doesn’t leave any, but it seems to evaporate more thoroughly.
7) If you must evacuate before recharge, consider replacing the dryer/filter in the condenser bay (3 right) – Prevost Parts.
8) Don’t chase compressor clutch and condenser and evaperator fan failures until they fail with a fully charged system.
Caveat – yours might be different.
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Charged it today. Coach ac is still 20f delta input to ouput and dash is 10f still. So nothing changed other than the condenser fans no longer cycle. The lower recv site glass red ball is floating high and no more bubbles in the dryer site glass. Its 85f outside and the low reads 35psig w/high reading 210psig, R134a chart says it should be 45-55/225-250 @ 85f, so I am off there based on the chart.
I cant find a filter for the dash air on this coach. I remove the narrow vent at the base of the dash and I can’t find anything that resembles a filter….
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The 20 degrees is good. FWIW my low side pressures at a 70 degree ambient are running 30 to 35. Red ball in the middle. High side I think was 180 to 190 but that’s going by memory.
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What should dash air readings be with 134 30/125 or higher
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David,
The readings are based on ambient temp and humidity.
Google R134a pressure chart, find one that includes humidity, because the higher the humidity the higher the low and high side pressures will be for a given ambient temp. Here is an example of one:
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Michael,
did you ever resolve the cooling issue with the dash air part of your OTR? Mine is exhibiting the same symptoms.
Gerald
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