Low Pressure Cut off Switch??
Thread Starter
Racer
Joined: Jul 2000
Posts: 416
Likes: 4
From: Iron Mountain,Michigan
Low Pressure Cut off Switch??
Hello Fellow Vetteheads,
Have a air conditioning question for you today. I have been fooling
around with the air on the Vette since it stopped working from last year, just because I do not like things that do not work when they are supposed to. Anyway when I turned on the air conditioner, nothing, disconnected the power to the low pressure cut off switch and jumpered the the compressor and it started fine. Obviously the pressure switch is either sensing a low pressure condition or it is shot. Could I get some understanding from one of you air conditioner GURU'S PLEASE. Thank You in Advance.
Peter
Have a air conditioning question for you today. I have been fooling
around with the air on the Vette since it stopped working from last year, just because I do not like things that do not work when they are supposed to. Anyway when I turned on the air conditioner, nothing, disconnected the power to the low pressure cut off switch and jumpered the the compressor and it started fine. Obviously the pressure switch is either sensing a low pressure condition or it is shot. Could I get some understanding from one of you air conditioner GURU'S PLEASE. Thank You in Advance.
Peter
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
RPM on the engine has nothing to do with this switch. Most are adjustable on low setpoint, but 20 psi would be about right for R12 if not a tad low. You need some gauges to see if you have a charge in there. Static system sitting for a while should have 70 psi or so on both the low and the high side. Sounds like you either have no or not much charge or if you do the switch is bad.
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
At idle, you will see higher " low-side" pressures, as the a/c compressor is not efficient yet. The reason I set the low side at an elevated rpm is to insure airflow across the evaporator. As engine rpm increases, so does the a/c efficiency. The low side will drop, perhaps lower than the cut-off point of the switch. This procedeure is explained in the Chevrolet service manual.
Melting Slicks
Joined: May 2002
Posts: 2,716
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
The switch is to prevent the evaporator coil temp from dropping below 32 deg and freezing the condensate on the coil, it does this by cycling the compressor clutch. They are set at about 18 psi for R-12. System pressures will be drastically affected by cabin temps and under hood temps. System pressure will vary a great deal while sitting without the compressor running. To trouble shot the system correctly you really need a set of service gauges to see what is going in with the system.
Neal
Neal
