Ah! A/C

Hello to all of you fine car talkers,

I am having trouble with my A/C this time.

I am not getting any voltage at the compressor. I am getting voltage at the fuse and the fuse is fine. I am getting voltage at the pressure switch connector on the condenser as well. I checked the resistance at the pressure switch and the multimeter is showing the same reading (1.0) on any scale whether the a/c is on or off. When I jump the electrical connector at the pressure switch, I am getting nice cold air in the truck. I am not sure how much pressure I have in the condenser but when I tried to add refrigerant, the system seemed to be full (there is no gauge on my refrigerant tool, though, and when I tried to add some, the compressor was not engaged).

Now, does this mean that the pressure switch needs to be replaced? If yes, is this something I can do at home or do I have to bring it to a mechanic? I have a feeling that all the refrigerant is going to escape from this pressure switch if I do it myself.

Should I try to add refrigerant while jumping the pressure switch, so the compressor will be engaged? (I am saying this in case you think there might not be enough refrigerant).

Any advice would be appreciated.


Make, Model, Model-Year, Please.


It would be nice to know what year/make/model of vehicle you’re talkin’ about?


Oh yes, sorry. It’s a 1992 Chevrolet C2500, 5.7L V8 engine.

Try tapping on the pressure switch and see if the A/C comes on. You can also jump it briefly to see if it is bad.

You can’t use a multimeter to measure resistance in a circuit that has power on it.

BillRussel: Does the pressure switch has power when it’s unplugged (but still on the car)? Should I unplug the battery then?

SteveC76: Thank you for your advice. I will try tapping on the pressure switch and see what happens. I am not sure to understand, though, what you mean by jumping it. Do you mean bypass it? (Which is what I have done). Or do you mean something else?

My mistake: When I wrote condenser in my first message, I should have written accumulator.