I just installed a classic air A/C system in my 69 camaro. I had a A/C mechanic evacuate the system and add R134. The instructions said to add only 24oz. After the third (8oz) can the compressor never kicked on. We jumped the high/low pressure switch and the compressor came on. We ran it for awhile and the low pressure side read 12 pounds and the high pressure read 145 pounds. The system was pushing out cold air but when we took the jumper wire off and connected back to the high / low pressure switch the compressor did not work. I called classic air and they said the high / low switch is bad. I am not sure thatthis isthe case because the low side only reached 12 pounds. We added one more 8 oz can and low side went to 17 pounds and the high to 260 pounds. I talked to other A/C shops they say it could be the expansion valve. Any thoughts on this? Please Help, this is driving me nuts!!!!!!!!!!

 

I do not know what type of switch Classic uses, but I would suspect it to be a trinary switch. Make sure you have used the correct two terminals on the switch.

The expansion valve will not stop the compressor from kicking in. One can should have been enough to close the contacts in the switch. The AC tech should have stopped there to investigate.