A/C has me stumped.


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Well-known member
Sep 3, 2018
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My Car
72 Mach 1 Q code, Original owner
I just replaced most of my A/C components in my search for cold air. I replaced the TXV, condenser, compressor, filter, and flushed the lines and evaporator with solvent and lots of shop air. Some dirty stagnant oil in the evaporator, but no other surprises. Evacuated the system for an hour, holds vacuum overnight. Charged the system with R-12 ( my system is original with a York 210 compressor). My gauges read 80psi low side and 75 psi high side, engine running, warmed up, 85 degrees ambient. Pressures rise +/- 5 psi at higher rpm (2500). My old compressor showed similar behavior and the manual indicates a low High-side pressure with a high Low-side pressure indicates a blown head gasket. So on my old compressor, I replaced the head gasket and valve plate with no different outcome. Finally I replaced the compressor with a new one. Manual says if TXV stuck closed, I’d see a vacuum on the low side, so that’s not it. It seems like if it were the head gasket, a new gasket and valve plate would resolve this, but it didn‘t. Even a new compressor had no impact. My high side line is hot to the touch when running and the suction line is barely colder than ambient. If the system were undercharged, the manual says both readings would be low. No bubbles appear in the sight glass. So, my wise and educated 71-73 owners, what do I test next?