911 A/C Troubleshooting
 

Ok, A/C experts, we need a little help here. On my '80 SC coupe, the a/c functions, but only blows warm air. Gauges indicate a high side pressure of about 240 psi at 90 degrees ambient temp and a low side pressure of 45 psi at the same temp. The compresser was replaced with a Sanden 507 and the original hoses were replaced with barrier hoses about 3 years ago. A pro cooler was added 2 yrs ago. The system does not appear to be leaking refrigerant and the front condenser fan is working properly. The condensers and evaporator fins are clear of debris and are clean. The only two things that I can think of that may be causing the warm air is 1) a clogged expansion valve or 2) a bad temp switch. Any other thoughts?

Thanks,

Is your Compressor engaging?

A/C Troubleshooting
 

The compressor clutch is engaging properly, the belt is tight and no funny noises are being made!

I'm not an expert only a newb but based on what you are saying and what I'm going through I would say expansion valve.
Especially if you are getting that high a low side pressure at 1500 to 2000 rpms. It should be lower.

Is this R12 or a R134A conversion?
A clogged TEV will cause an extremely low side pressure (<20psi) and very high discharge pressure (>300 psi)
Your low side is a little on the high side. You should get at least 30psi to get a cold 45F supply air temp.

Also, maybe the heater flap is slightly open and mixing with cold air because at 45psi low side, you should get at least some cool 60 - 65F supply air temp.