OTR Air Issue

[DaneB]

95 Marathon which has been changed to R134a by the previous owner. Getting the coach ready for a trip I noticed that my compressor was off on the low pressure. No gas in system. Found the leak at the sight glass fitting on the drier, it must have vibrated loose. Leak checked, vacuumed and recharged the system with approximately a complete 28lb charge per the manual. Again this is a converted refrigerant system and not sure if it was converted properly.
Driver air is blowing very cold but the coach air is at most barely cool. I have checked the heater core with hand touch and it is not hot whatsoever. I have not completely shut down the hot water valve but common sense tells me that hot to touch would be hot to heater core and if my valve was sticking the heater core would as least be hot to touch. Do not think I have a water valve sticking. I am pretty mechanical and have a very good understanding of this OTR system.


I have a series of questions as I am at loss even understanding refrigeration quite well. Some questions are technical but I know that there have to be a great number of members on here that do their own maintenance.

- Where is the expansion valve for the main evaporator? It is not in either air control bay. I have found the driver valve under the front and per the service manual the coach valve is in the driver side bay 3 with the evap fan and equipment.
- Is there an accurate pressure reading that I can get my gauges close to on a normal 90 degree sunny day?
- Could I have the system overcharged? I read a PDF tech sheet that says liquid is to be at mid point of bottom sight glass on receiver tank? I have a sight glass on the top of the receiver tank as well, with a small ball inside and I am almost certain that I saw this glass full before my leak, the top sight glass was full of liquid and the ball was vigorously moving about the glass. Again I put what I estimate as 28 pounds of R134a.
- If overcharged would the driver evaporator get that cold yet leaving the coach evaporator not getting cold. Overcharge is as bad as undercharge but I would really expect the driver air to loose cooling as well.
- Do I still need a little more refrigerant and have I under charged the system? From the cooling of the driver air I feel this is not the case.
- Do I have a faulty expansion valve and I also have read and seen mention of a liquid valve? Can I check this manually?

HELP and what am I missing?

[dale farley]

Dane,

I've never had a bus with Prevost OTR air, so I can't be of much help to you. Hopefully, some of the ones that have OTR air can tackle at least one of the questions you have in the above post.

I do know that on an automobile with 134a, on a 90 degree day, the low pressure should read about 45-55 and the high side should be 205 to 250. I assume this should be approximately the same.

It is very easy to over charge without realizing it, because you may not notice the outlet temperature starts going up until you have already passed the max capacity. I took my bus to an automotive AC shop last year and had them check the pressure and freon level of my dash air. The service charge was only $35 and it worked great after they added some freon.

[JIM KELLER]

Dane, Since you are not getting much response on this issue and it sounds like you are a technical person I suggest you contact one of our Sponsors with your questions.

[Gil_J]

Ditto to what Jim said. You can ask Ben he's at Parliament Coach in Clearwater, FL.

[DaneB]

Thanks Gentlemen and an update after day 3 of my "stubborn persistence" says my wife. I told her I was just trying to save her a few thousand $ and she said "Carry on then!!!"

I found the access door and the expansion valve which had a slightly cracked tube at the bulb. Unfortunately the bay and all its beauty had to be almost torn out because the access door top screw was behind all the build-out material that finishes the entertainment bay. A few pried out screws that were hidden behind the carpeted built-ins is the extent of the damage, which is a blessing considering my 4 hour search and demo to get to the valve. I will be driving to Marathon in San Antonio, FL tomorrow to pick up a new expansion valve on my way to Panama City Beach for my Labor Day weekend that was supposed to be in the coach but instead in my truck with the air on Max and my air conditioned seat on medium because it is stinkin" hot and humid down here right now. With the OTR failure, I also simultaneously had a front CruisAir compressor failure. So new condenser on order and time for a few cocktails so I can prepare for the future repairs. The refrigeration level is TBD until I can get the expansion valve to let refrigerant into my main evaporator. Have a great weekend and join the other half of the country and don't labor!

[JIM KELLER]

Welcome to POG Dane ! Your humor and expertise will fit right in.

[Gil_J]

Dane,

Persistence and patients are a must for those wanting to discover the inner workings of their conversion. You seem to have both.

Enjoy PCB. If you are a country music fan they have a great concert this weekend.

Gil