I am trouble shooting my a/c system in my 87 Pontiac Firebird.
With the key switch on I moved the slider switch to both the Max a/c and a/c positions. The cooling fan comes on , which is normal but the compressor is
not coming on.
I ran jumper wires directly from the battery to the compressor. The clutch engages and the compressor works.
Next, I disconnected the plug from the pressure switch on the accumulator and
used a jumper wire connecting the two contacts of the plug and there's no voltage.
Is there a relay in the system that when closed provides voltage to the wiring going to the accumulator pressure switch? I also checked the 25 amp a/c fuse and that is good.
Just need a little help on trouble shooting this. Thanks.

George

 

 

Are you sure that you have enough R12 or R134a in your system? Yes, jumping the low pressure switch should cause the compressor to turn on and stay on in the Max AC setting. If you use a paper clip to jump the sensor, it should turn the compressor on regardless of the level of refrigerant. There should be a sight glass somewhere in your system (usually by the suction accumulator) that you can use to see refrigerant flow through the system. If it's low, the low pressure switch/sensor will shut the compressor down.

 

Thanks for the reply. These cars did not use sight glasses. I converted this system years ago to R-134. The pressure switch on the accumulator has continuity, meaning the switch is closed , allowing voltage to go to the compressor clutch. What I don't have is voltage at the wired electrical connector going to the switch on the accumulator.

 

Just checked the green wire going from the HVAC switch in the dash to the plug going to the low pressure switch on the accumulator and the wire is good with good continuity.
Looks like it could be the round switch mounted next to the fan switch.