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Motorhome A/C

treeman on Tue June 01, 2010 7:42 PM User is offline

Year: 1996
Make: Holiday Rambler
Model: 38 ft Motorhome
Engine Size: 5.9
Refrigerant Type: 134a
Ambient Temp: 83
Pressure Low: 41
Pressure High: 175
Country of Origin: United States

Hi I have a 38 ft motorhome 5.9 cummins diesel in the rear so it has at least 38 ft of lines I recently replaced the compressor(seltec),drier,expansion valve I had a guy at a local auto shop vacuum and charge for me We couldnt find how much freon and oil to add anywhere The guy who sold me the compressor suggested 15 oz of oil I put 16 The guy at the shop ended up putting in 7.5 lbs freon The vent temp was 55 outside was 81 I checked the pressure it was 45 low 225 high I thought he might have added a little to much so I let a little out to 41 low 175 high outside 83 vent temp 53 Is this as good as its gonna get? I dont know what to check or do next?

JACK ADAMS on Wed June 02, 2010 11:10 AM User is offline

Leak check the system would be the next step. The refrigerant system charge looks good to your readings and vent temps. Remember that you have a lot of BTU space that you are trying to cool down, so it will take a wile.

chris142 on Wed June 02, 2010 11:30 AM User is offline

Ya those have a huge space to try to cool down. Make sure that your not getting hot water into the heater and that any blend doors are sealing well.

bohica2xo on Wed June 02, 2010 11:36 AM User is offline

Set the high idle to 1500 engine rpm. Run the system with the cabin fan on the highest speed. After running the system this way for 10 minutes, record the high & low pressures while the engine is still @ 1500 rpm. Record the vent temperature as well, and post the numbers here.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

treeman on Wed June 02, 2010 2:18 PM User is offline

Im not sure what happened but when I checked it yesterday the inside of the rv was hot so I let the roof ac run all night and now its 70 inside soon as I turned the dash ac on the high side went to 300 and the low side went below zero and the expansion valve iced over I turn off ac for about 30 min tried it again high side stoped at 250 low still below zero expansion valve still frozen Is the valve stuck? Moisture?

NickD on Wed June 02, 2010 5:40 PM User is offline

Seems like on motorhomes, you really don't know what you have until you look. System on my Pace Arrow uses a York compressor, outputted to the condenser, the receiver, the expansion valve, evaporator, then back to the compressor.

Controls are minimal as well, no low or high pressure switches, climate control applies 12 V to the clutch coil through a thermal switch with a sensor on the evaporator. Compressor will run even without refrigerant in it, but doesn't hurt a York since it has its own oil sump, but you won't get any cold or even cool air. Only thing that will shut if off besides the switch on the climate control if the evaporator sensor sees less than 33*F on it. That wasn't working for awhile, but the blower volume would go down due to evaporator icing, so I switched it off manually until the blower air volume increased again. But did make a low temperature sensor for it that works, kills under 33*F and switches back on a 38*F, one less thing to do while driving.

The expansion valve acts to regulate the liquid refrigerant flow based on evaporator temperature, the cooler the evaporator gets, the less the flow. It also tries to keep the low side pressure at 30 psi by opening up at higher temperatures unlike a fixed orifice that will skyrocket the low side when it really gets hot outside. It should never freeze up unless you have moisture in the system, how long did your guy draw a vacuum? I would do it at least 3 hours, but I like taking naps.

And what kind of compressor was in there, did it have an oil sump in it? Have to watch that on these systems, should have a dual function switch if it depends on recirculated oil to survive. I don't know what you have, but sure would look first. Another nasty thing is your new compressor may be falling apart and plugging your expansion valve due to lack of lubrication, I don't know, didn't see it.

You call the motorhome company about the AC, they don't know, say it came from the chassis manufacturer, call them, they don't know, the motorhome company put it in, so you go around in circles trying to figure that out for the refrigerant and oil capacity. Least with a York, know if it has the correct amount of oil in it or not.

Tell me I am not of much help. Know its frustrating, somebody put that system in.

treeman on Wed June 02, 2010 6:33 PM User is offline

Im pretty sure the expansion valve is completly stoped up I turned the system off let it set 2 hrs the low had 80 the high had 150 I let the pressure off the low side completly with the low valve open the high side still has about 140 I hope that nothing else tore up and maybe I just missed getting it blown out from before I blew the lines and stuff out with air 120 psi

JACK ADAMS on Wed June 02, 2010 6:45 PM User is offline

Expansion valve is bad and needs to be replaced. The system should have been flushed with a good flushing solvent like Hecat. Prior to installing replacement parts. Blowing out is not a form of flushing.

Edited: Wed June 02, 2010 at 6:46 PM by JACK ADAMS

bohica2xo on Wed June 02, 2010 8:02 PM User is offline

And back to square one you go. Long line motorhome systems are always a challenge, and the work must be done carefully.

Now you need to break the system down into individual components, and flush everything (EXCEPT the Compressor!) back to bare metal. Get all of the oil, debris & flushing solvent out of the system before you put it back together.

The TXV may have an inlet screen, but it sounds like a solid blockage. Whatever the blockage is, it came from the system. You need a through flush. That trash could have taken out the compressor, and something in that system still could.

Where is the receiver / dryer mounted? Does it have a sightglass?


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

treeman on Wed June 02, 2010 8:49 PM User is offline

Yea I wish I would have found this site before I started Ive worked on alot of stuff but this is my first real a/c work im learning the hard way I took the TXV off and it was completly stoped up with white powder im geussing its stop leak During the process I forgot to replace the schrader valves and noticed one was leaking so I put some stop leak in it stoped the leak I normally wouldnt use stop leak but didnt want to drain the system again

bohica2xo on Wed June 02, 2010 8:59 PM User is offline

Ah, the plot thickens. So does the refrigerant...

Sealer. Stop leak. Magic in a Can.

You might as well open the system, and shovel the contents of the cat box into the lines. Actually, that might be easier to remove...

You have a LOT of clean up to do now.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Wed June 02, 2010 9:59 PM User is offline

Still haven't stated whether your old compressor was a sump type or why you had to replace it. If it was siezed or even difficult to hand rotate, its the culprit for killing your new compressor.

JACK ADAMS on Thu June 03, 2010 11:24 AM User is offline

Stop leak is one of the worst things you can do to an a/c system. Flushing is one of the most important parts of doing an a/c service. Need to make sure all components are clean and free from any foreign matter. Good luck!

treeman on Thu June 03, 2010 5:54 PM User is offline

I started not to even post this but oh well Im leaving on a trip in the rv sat. I asked the guy at the local parts store about some flush he said he has never heard of it so I put a new TXV on bought a cheap vac pump and recharged it I know I know but im headed out west and driving right into the sun if it will work 1 day it will be worth it Anyway after charging it again at idle it has 37 low 179 high 92 outside 70 inside vent temp 49 and at 2000 rpm 30 low 210 high vent temp 43 Thats the best #s since ive had it I ended up only using 90 oz of freon Ok let me have LOL

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