[William]

I don’t think so. If I am not mistaken your coach has a switch for heat or AC and when you select AC the compressor runs and coolant heat is introduced to the air flow to modulate the temp as required.

This is a guess……..

[kenneth]

Yes Jon, I have that switch. About 3/1 left Naples with otr on heading up 75. When we got to 10, it was 7:00 pm and much cooler than when we left. I noticed the yellow a/c light on, so I assumed the Freon charge became too low to engage the clutch. Shut it off.

Assuming it needed a freon charge, today went out to fill it. Before spinning the 05g, I gauged the high and low side to be the same at 55 pounds (ambient 65). Then fired the system and pressures went to normal for the ambient and the accumulator site glass ball was at normal operating. So not low on Freon. Thus the original question.

Operating normal now – self fixing.

[Archived]

Sounds like a low pressure switch?

[Archived]

Thanks for that idea Jon. When it happens again, I’ll swap it.

[DON]

Having a leak down issue with my 1991 XL (88,000 miles) with OTR leaking down and called Prevost Fort Worth last week to get into there for service. Service manager said they usually have at least 80 hour labor charge to change out hoses , compressor and related goodies. Said they change out compressor also. That didn’t sound right. Doesn’t seem to have any oil around seal. Mine works, as I told him, but will leak down in a few days. At $10,000 labor alone and Labor could be more if they have to tear anything out to get to some hoses. It could be around $20,000 grand with the parts. Have freon gauges, 2 stage vacuum pump, and nitrogen and a nice new Bus Barn and think I’ll give it a shot.

[DON]

Dan and Barb, Based on the temp and pressure you mentioned, it sounds like the system is a little low on R134a, and the low side pressure switch is shutting the system off. All refrigerants have a static temperature-pressure relationship. R134a gauge sets have a pressure-temperature chart on their face, or you can print one online like :

https://www.forane.com/export/shared/.content/media/downloads/products-documentations/fluorochemicals/forane-134a-pressure-temperature-chart.pdf

At 65f, the static pressure of R134a should be about 64psi.

When OAT temps are cool, its easier for an under serviced HVAC system to hit the low side pressure switch limit.

[Archived]

If the pressure gauges are reading OK and if the red ball is floating in the lower sight glass of the receiver when system temps have stabilized it is unlikely the system needs refrigerant, however the pressure switches do seem to have a habit of inaccurate functioning.

[Jerry]

Thanks for your input Don. I printed that chart for future reference. The chart I was using yesterday was for a running system. After firing it up, the low side was showing 37 psi and was prexactly in line with the chart. And with the ball in the right place I was so happy, I just quit. So I’ll wait for it to mess with me again, prolly Petosky in August.

[Archived]

Glens, your numbers are reasonable based on my experience. Your system started life with r12. A change to r134a would require changing the oil in the compressor to the correct spec, replacing both expansion valves, replacing the dryer/filter, and replacing the hoses. The one inch inside diameter aeroquip hose that runs from the condenser bay to the evaporator bay is the most fun. I was at Prevost Saint Nicolas for that and they had to remove the 208 gallon fuel tank and cut an access hole in the stainless at the back of the evaporator bay to get to the fitting.

If your hoses are not compatible with r134a they will leak through the hose material rather than at the fittings/ends. Good luck.

[Archived]

Thanks Dan for the info. Had my converted back in 2013 to R134 but know they only replaced the easy hoses on the compressor in the back. Don’t think they replaced the valves. It has lasted 4 or 5 years with the present set up. Would still freeze you out until last fall when it started dropping freon slowly. Now in about 3 or 4 days to compressor cut out. Won’t leak down below about 30 pounds in system but low enough that compressor won’t kick in. Thanks again.