Rep Power: 0

I determined my thermal limiter on the compressor is bad. (Possibly from the heat of my alternator seizing up and catching on fire? already fixed that)
Before investing the time and money to replace the thermal limiter, i wanted to make sure the rest of the AC was functioning properly. Its my sons car, just bought it cheap, if the AC requires more than $200, he can roll down the windows old school style...
So i jumped/bypassed the thermal limiter for now to test. AC cools fine in the car, fans run, all seems good. But i did want to know if the compressor or anything else was on the way out before replacing the limiter.

Hooked up my pressure gauges and here is what i got ; today was 70 degree day, maybe 30% humidity.
Rest pressure/car AC off : 70 PSI - both sides, seems about right
Ac running at idle : low side 15 PSI ; hi side 125 PSI - cold air from vents, seems ok

Here is where I get concerned:
AC running @ 2000 RPM
Low side drops to ZERO PSI on gauges, high side come up to about 165 PSI
A Little "wobble" on the high side, but not a lot like i have seen or bad compressors in my past experience.

Any thoughts on what is causing such a low pressure at speed?
Again, don't want to spend the time on a thermal limiter if it looks like i will need a bunch more work, but also don't want my kid driving it with the limiter bypassed in case the compressor is about to seize up and throw the alternator belt.

Yes, i know gauges are not the best way to test if the refrigerant is topped off, but dont want to pay for a vacuum and fill by weight if there are other serious problems obvious. I was assuming 70 PSI at rest @ 70 degrees mean the capacity is close enough that it should still not go to zero on the low when running.

Any help appreciated. Im pretty mechanically inclined, but AC is not my forte...

 
Rep Power: 518

Pressures are probably the second best way....

Was the engine compartment was stone cold when you took this measurement? If so, then yes that's about perfect.

If the engine had been running and the compartment was hot, then your static AC system pressure should have been significantly higher than this.

http://www.pacificseabreeze.com/tech...a-PT-Chart.htm

Hard to tell without being there, but I'd guess the expansion valve may be stuck closed or nearly closed.