Need help troubleshooting A/C issue

80skeys · #1 03-30-2010, 10:32 PM

1991 Silverado K1500. 5.7L. Automatic. 4x4.

I'm trying to get A/C working. Here's what I've done and observed so far:

- the blower is fine and all the dash lights appear to be in working order.

- I put refrigerant in the system up to recommended pressure. This was a couple hours ago and gauge shows it's still at the same pressure now, so hopefully this means there's no leaks

- took a test light to the connector at the Evaporator. Lights up when AC button is turned on. Does not light up when AC button is off.

- compressor clutch is not turning. took a test light to the connection at the clutch. It does not light up under any circumstance.

So I'm thinking there's an electrical problem because power is not going to the compressor clutch. Any ideas where I should look?

I'm also thinking it would be useful to test the compressor with a different source of power. Any thoughts on this? Is it a good idea and if so, how should I do it?

thanks

80skeys

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Mr_Shamrock · #2 03-31-2010, 07:11 AM

A common thing on these systems is the low pressure switch going bad. It is plugged into the accumulator. You can test it by unplugging and jumping the 2 wires from the harness side together. This should send power to your compressor. If it does then replace the switch. They are fairly cheap.

80skeys · #3 03-31-2010, 08:10 AM

Quote:

Originally Posted by Mr_Shamrock

A common thing on these systems is the low pressure switch going bad. It is plugged into the accumulator. You can test it by unplugging and jumping the 2 wires from the harness side together. This should send power to your compressor. If it does then replace the switch. They are fairly cheap.

Excellent suggestion. By "harness side" do you mean jumping the two wires that are unplugged and hanging loose?

Mr_Shamrock · #4 03-31-2010, 01:55 PM

Quote:

Originally Posted by 80skeys

Excellent suggestion. By "harness side" do you mean jumping the two wires that are unplugged and hanging loose?

Yes don't jump the switch itself because once it is unplugged it does nothing. Jump the 2 wires in the harness that you unplug from that switch. Seems like common sense, but I have had a guy that I told that to and he was jumping the switch not the wires.

80skeys · #5 03-31-2010, 02:42 PM

Okay now I see. those two wires complete a circuit going to the compressor. Okay I jumped them and the compressor clutch came on. The low side pressure dropped to 0. I hooked up a can of refrigerant, but the low side pressure keeps dropping to 0 as I add more refrigerant.

Mr_Shamrock · #6 03-31-2010, 07:12 PM

It's taking the freon though?

80skeys · #7 03-31-2010, 07:30 PM

Quote:

Originally Posted by Mr_Shamrock

It's taking the freon though?

I can't tell. When I depress the button on the can, the pressure temporarily goes up, then quickly drops down. I stood there for about 10 minutes putting (or thinking I was putting) freon in the system, but there still seems plenty left in the can afterwards.

Mr_Shamrock · #8 03-31-2010, 07:35 PM

It's hard to diagnose without being there. It is normal when the system is low for the low side to go to zero, but it could also mean that you have a blockage somewhere. It is also normal for it to take a while to charge. I just repaired my dad's Suburban which holds 4 LBS (dual A/C) and it took about 35 minutes for it to suck it all in. What is the A/C history on this truck? How long has it not worked? Have you added Freon before?

80skeys · #9 03-31-2010, 08:59 PM

Oh gee, if that's the case maybe I didn't give it enough time. I did notice it seemed to be holding about 10psi after I was charging it.

Mr_Shamrock · #10 03-31-2010, 09:18 PM

After it takes a little freon you should be able to plug the low pressure switch back in and let the compressor cycle by itself. Unless the switch is bad of course.