Hello I’m new here but I need some input or advice on what to do!! So, I have a 1991 Chevy c1500 2wd with the 350! The ac was retrofitted for r-134a by the last owner, ac stopped working around 3 months ago now. But I took it to my school and diagnosed it and reset the AC button in the interior, ac kicked right on. We recharged it there and it ran fine all the way home, but I did realize the AC wasn’t cycling off, I’m wondering where my next step should be or where I should be looking. We thought it was low or overcharged so we recovered the Freon and recharged to proper level. Same issue tho, ac blows nice and cold but I’m worried the compressor not cycling will build high pressure and blow a line. But what I did notice when I hooked up the machine to the low port it was extremely high on pressure. I’m guessing this is because the AC wasn’t cycling off at all? Thank you in advance!

 

My 1996 C1500 A/C compressor only cycles on/off if it is low on R-134a. I know on more modern vehicles like my wife's 2012 Subaru, the compressor seems to cycle on and off quite often. But I don't see it on my 1996 C1500. I think it is just a design difference. I don't think my 2006 Silverado A/C cycles the compressor either.

If the AC is on max cool, and the coolant charge is right, the compressor on these trucks tends to run continuously. With the coolant charge right, the max pressures on both high and low side are reached in a matter of 15 to 20 seconds after the compressor engages, so I don't think pressure is a concern just due to running longer or continuous cycles. I've observed that when charging and diagnosing them with my gauge set as well. Newer vehicles tend to have climate control that turns the compressor off when you reach a set cabin temp. On my trucks, there is no internal cabin thermostat, so it just keeps blowing cold air forever.