My recent work with dashboard controls revealed to me that the AC isn't working. It is an R12 refrigerant system, with parts from about 1986 and 2008.

R12 is tough to come by. There are technical reasons why it's hard to "upgrade" an R12 system or using R12 components with R134A causes problems.

What I've found, is that GM built the 1999 C7500, sometimes using the same form factor Sanden compressor, along with the other parts.

I wanted to denote the part number for this compressor. I'm considering doing the change over of all the components. The GM part number is 15020478, Four Seasons calls it 68594, and to Fleet Pride, it is the OTRCO1008.

Happy Motoring!
Matt

They made a big deal about converting a R12 system to R134a changing the expansion device is not necessary, one might lose a few BTU's but no big deal these chassis systems were not that efficient anyway. The only thing that is really required is to purge the system and replace the oil with mineral oil for R134a. A big deal was made about the smaller cells in R134a but if the r12 system didn't leak its a long shot that R134a in the system will. New fill devices are required to show others it is a R134a refrigerant.

Like most folks with these old dash systems, I just let mine not function, run the generator and roof A/C when needed.

Roof air is a back up, but if your generator goes down, dash air is needed to keep you cool. Do not expect dash air to chill your whole coach.

To get the dash air back up and running, I suggest replacing the compressor. Use the recommended PAG oil, for the compressor you purchase. There are also recommendations on additional oil because of the length of larger systems. Generally the compressor is a Sanden 709 squash plate compressor. Your roughly 30-year-old compressor is likely leaking at the front seal. Other components will be fine if you can draw the system down for a day or two and the system holds a vacuum over night with the vacuum pump disconnected.