A/C pressure cycling switch

[Alek M.]

I have problem with 92 Buick LeSabre A/C system, need help, please.
It works randomly...
R12 level is OK.
Is it that pressure cycling switch or relay are not good.
Where exactly are pressure cycling switch and compressor control relay?
Thanks.

[mcqueary]

Hi.

Yes either the relay or the pressure cycling switch could cause your problem among other things. I'll tell you where these components are on a 93 Lesabre and I think they should be the same on the 92. The compressor relay is in the engine compartment. It is the rightmost relay along the firewall (passenger side). An easy test to see if this relay is bad is to swap this relay with the horn relay which is right next to it (assuming your horn works OK).

The compressor cycling switch is mounted on the accumulator which is the silver "bottle" near the passenger side firewall. Disconnect the connector and short the pins on the cable harness connector to see if this allows the compressor to work. If so, a bad switch or a low charge is indicated.

You may also have a too large a clutch air gap, a loose electrical connection somewhere, corroded contact somewhere, intermittent high pressure cutout switch, bad HVAC programmer, or even a bad PCM, but the relay and the cycling switch are fairly easy to test. Let us know.

Incidently, on my 93, I have found several of these engine compartment relays that had high contact resistance so that's a good place to start. If possible, I recommend checking these relays by removing the relay, applying 12 volts from the battery to the coil, and measuring the contact resistance with an ohmmeter. You may be surprised to find high resistance! This can certainly cause erratic or no operation depending on how much resistance is in the contacts.

[imidazol97]

>Incidently, on my 93, I have found several of these engine compartment relays that had high contact resistance so that's a good place to start.

You might check the relay in the relay center on the firewall at the passenger side. That is the on/off switch for the compressor. I had a 93 where the air didn't turn on occasionally and would warm up and then turn on after it had tried to make contact for a while. Then after a few weeks of occasional warm air for a minute or two, it wouldn't work at all one very hot day after sitting and idling with engine compartment very hot.

The relays that have the same number can be interchanged. I.E., the 3rd and 4th are relays that turn the inside blower motor on and off. You could switch one of those for the compressor relay to see if that fixed your problem. The relays can be removed by using a thin blade under them and twisting up to raise the prong of metal that snaps down and locks over a tang as you push the relay in.