A/C Pressure Switch
Thread Starter
Racer
Joined: Nov 2008
Posts: 442
Likes: 6
From: jacksonville Florida
A/C Pressure Switch
I Just charged my a/c system and I think the pressure switch/ clutch cycle switch is bad? The compressor will kick on then kick right back off again and it just keeps doing this, if i bypass the switch and just bridge the two terminals of the boot that plugs into the switch, the compressor turns on and off just fine with the a/c controls in the car. Does this confirm the switch is bad? and if it is should I replace with the OEM switch? I have since swapped my system from r12-r134a. I replace the compressor, orifice tube, and accumulator when i did it but not the switch.
Melting Slicks
Joined: Oct 2000
Posts: 2,142
Likes: 195
From: Englewood FL
I would hook up a set of manifold pressure gauges to the system and monitor the pressures when the compressor cycles off. If the low side drops much below 30psi the compressor will cycle off. If so the system is low on freon. You can compare the low and high side pressures against the readings on a pressure chart to see if they are in spec.
Burning Brakes
Joined: Oct 2012
Posts: 1,152
Likes: 252
Hook up a gauge and see what it is reading. 134a in a R12 system will run higher pressures. In another R12 car I have the compressor would cycle on/off a lot due to exceeding the safety switch limit when I ran all 134a. I now run a blend of propane/134a and keep it underfilled slightly and have no more issues.
https://www.corvetteforum.com/forums...my-1969-a.html
R
https://www.corvetteforum.com/forums...my-1969-a.html
R
Last edited by Dynra Rockets; Feb 20, 2018 at 09:06 AM.
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
Thread Starter
Racer
Joined: Nov 2008
Posts: 442
Likes: 6
From: jacksonville Florida
OK so when i plugged in the low pressure gauge it was initially sitting at 80 psi.
I bypassed the switch and engaged the compressor. Pressure dropped and settled at 6 psi. I ran it for 3 minutes and it stayed steadied at 6 psi, so it looks like my system is low?
Then when I turned the compressor off, the temperature rose and settled at 49 psi.
I bypassed the switch and engaged the compressor. Pressure dropped and settled at 6 psi. I ran it for 3 minutes and it stayed steadied at 6 psi, so it looks like my system is low?
Then when I turned the compressor off, the temperature rose and settled at 49 psi.
Last edited by pleasants9; Feb 20, 2018 at 12:08 PM.
Thread Starter
Racer
Joined: Nov 2008
Posts: 442
Likes: 6
From: jacksonville Florida
update: Went ahead and added another pound. Got the low side pressure up to 30 psi and holding. The compressor now cuts off when i raise the rpms up to about 2000rpm the pressure drops down to 20psi and the compressor cuts out. Wondering if I should add about another 1/2 pound.
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Drifting
Joined: Feb 2007
Posts: 1,498
Likes: 206
From: Pearland Texas
St. Jude Donor '09
update: Went ahead and added another pound. Got the low side pressure up to 30 psi and holding. The compressor now cuts off when i raise the rpms up to about 2000rpm the pressure drops down to 20psi and the compressor cuts out. Wondering if I should add about another 1/2 pound.
Le Mans Master
Joined: May 1999
Posts: 6,692
Likes: 29
From: Texas
I think this would be a fairly fast diagnosis and fix, if low pressure, from a good shop. Know when I converted to 134, a quality shop did it, which did include a new switch (not the connector - see my other post elsewhere). This has now been at least three years and still do not need a charge. Did include a new compressor that has died. Its 80*already today in Houston and a/c is ice cold.
Last edited by Wrecked82; Feb 21, 2018 at 11:23 AM. Reason: spelling correction
Intermediate
Joined: Feb 2018
Posts: 36
Likes: 1
update: Went ahead and added another pound. Got the low side pressure up to 30 psi and holding. The compressor now cuts off when i raise the rpms up to about 2000rpm the pressure drops down to 20psi and the compressor cuts out. Wondering if I should add about another 1/2 pound.
Instructor
Joined: Jun 2018
Posts: 108
Likes: 17
From: Blue springs mo.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
this is an adjustable r12 low pressure switch. it is an r12 switch but can be turned down. 134 likes lower low side than 12. https://www.ebay.com/itm/181723260861
Last edited by derekderek; Aug 29, 2021 at 08:52 PM.