AC PRESSURE SWITCH QUESTION
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,144
Likes: 18
From: Panhandle FL
AC PRESSURE SWITCH QUESTION
Last year somebody had a post about adjusting the pressure switch. The story goes "you unplug the switch and adjust a little allen head that is located between the 2 terminals". This is suppose to change the cycle rate of the compressor so it runs a little longer and blows colder.
Does anyone know which way and how much to adjust this screw? Sounds kinda critical, if you over adjust you could blow a line. I think you turn it like a 1/4 turn but I'm not sure which way. ANYBODY
Does anyone know which way and how much to adjust this screw? Sounds kinda critical, if you over adjust you could blow a line. I think you turn it like a 1/4 turn but I'm not sure which way. ANYBODY
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Re: AC PRESSURE SWITCH QUESTION (SPEED750)
Counterclockwise reduces the threshold for compressor cutoff; clockwise increases it. Since it's on the low pressure side, you won't blow anything up, but if you're still using R12, it should allready be set to break the compressor circuit at 25 psi. Reduce it below that and the evaporator will freeze over and you won't get any air out of the vents (or what you do get will be hot). If you've switched to R134, it should be adjusted to cutout at 22 psi which is about a 1/4 to 1/2 turn counterclockwise from the R12 setting.
A manifold gauge set helps to get it right. Turn the a/c on high and open the doors and hold engine rpm at 1200 to 1500 rpms. Disconnect the blower motor harness and the pressure will drop until it reaches whatever pressure the switch is set at, cycling the compressor off. Note what that is on the gauge set and adjust the switch accordingly.
You don't have to turn the a/c or engine off to make the adjustment, just disconnect the switch harness. Compressor will stay off, adjust the screw, reconnect and recheck as above.
A manifold gauge set helps to get it right. Turn the a/c on high and open the doors and hold engine rpm at 1200 to 1500 rpms. Disconnect the blower motor harness and the pressure will drop until it reaches whatever pressure the switch is set at, cycling the compressor off. Note what that is on the gauge set and adjust the switch accordingly.
You don't have to turn the a/c or engine off to make the adjustment, just disconnect the switch harness. Compressor will stay off, adjust the screw, reconnect and recheck as above.
