A/C Compressor wont kick on when bypassing low pressure switch

Valkyn · 11-06-2009, 08:27 PM

The A/C stopped working in my car and I thought I would try putting a bottle of 134a in it. When jumping across the low pressure safety switch with the A/C on max the compressor wont kick on. I put a new A/C relay in and it still wont kick on.

The vent fans inside then cabin are also acting strange. Regardless of what setting they are on, 1-4, the fan speed is the same. The fan does come on tho, as I can tell a difference between having the switch set to off and set to 1-4. The HVAC fuse in the cabin was good, are there any other fuses that would affect this?

The A/C and fans were both working correctly a few weeks ago. Are there any things I could check to see whats going on?

fleetmgr · 11-06-2009, 10:30 PM

Test the clutch by taking it straight to the battery.

O2Form · 11-06-2009, 10:42 PM

Not sure what year car you are working on but on the newer cars that IS NOT a low pressure switch. It is a sensor used by the PCM to detemine if its ok to turn the compressor on. The value has to be within a certain range, you can't just jumper it.

Valkyn · 11-07-2009, 04:28 PM

How do you jump the compressor directly to the battery?

The car is a 95

fleetmgr · 11-07-2009, 07:33 PM

Unplug it, and make a couple of jumper wires. When you unplug the compressor, you'll see a pair of spade terminals, connect one to +, the other to -. It's easiest if you put aligator clips on the wires. Or, you can get ready made jumpers from Radio Shack.

When you connect it all, you should hear the the click of the compressor engaging. If the engine is running, you should see the center part of the clutch start spinning with the belt/pulley. If it doesn't, then time for a new clutch.

Valkyn · 11-09-2009, 10:18 PM

I havent had a chance to check the compressor yet, but this morning for some reason the fans seemed to be working again. When I put the AC on max it was really blowing out the air. After a few minutes it seemed to stop again. Could my blower fan be bad?

fleetmgr · 11-09-2009, 10:56 PM

Was the air cold?

Valkyn · 11-12-2009, 04:06 PM

The air wasnt cold.

Today I replaced the blower motor and that fixed my fan problems.

I jumped the AC compressor straight to the battery and it did engage, so what else could be keeping the compressor from engaging when I bypass the low pressure switch? Is the relay the only other thing it could be?

fleetmgr · 11-12-2009, 04:09 PM

Time to put some gauges on the system, but it's most likely way short of refrigerant.

Valkyn · 11-12-2009, 04:21 PM

Im sure the system is low, but how do I get the compressor to kick on so I can add more 134a?

fleetmgr · 11-12-2009, 04:25 PM

Quote:

Originally Posted by Valkyn

Im sure the system is low, but how do I get the compressor to kick on so I can add more 134a?

Hook the can up and it should start going in as long as the pressure in the can is above what's in the system. I wouldn't go there without having gauges, and there are other things you can do...but not without gauges as there is a risk of blowing up the can.

Valkyn · 11-12-2009, 05:13 PM

I just tried jumping the relay and the compressor kicked on. So would you still recommend hooking up a set of gauges? If the system pressure is under a certain level will it not kick on even when bypassing the low pressure sensor?

fleetmgr · 11-12-2009, 07:49 PM

Jumping the relay is the same as taking the clutch straight to the battery. Yes, you need gauges because you don't know where you're starting at.