2005 GMC 1500 Air Conditioning AC Not Working

[onecrazyfoo4u]

So I checked voltage on the connector that plugs in to the AC compressor. It gets 0 volts all the time, AC turned on or off. So then i pulled and checked every fuse and relay labeled AC or HVAC or Cooling Fan. They all looked good, so I swapped them with other known good fuses and relays (like headlights). All the ones I swapped with still worked, so I know the fuses and relays were all good.

 

Now I'm at a loss. Where do I check next? Fuses and relays are good, but no voltage to the compressor connector...and only 4.7v to the evaporator connector all the time. Is it a wiring issue or an hvac control panel issue?

 

I also noticed neither of the fans turned on each time I had the truck and AC running. Is that the problem? I'm so confused...

[muddkatt]

Jump the low pressure switch with a paper clip and check the voltage at the compressor again.

[hiking_mike]

If you short the low side and no voltage at the clutch, then another item could be the high side switch. This switch works the exact opposite of the low switch. I have this issue on my 95 chevy. I cant remember, but I think I simply cut the wires to the high switch and used a pig tail and shorted it out, but on the lead side instead of the connector side.

 

As a last resort. I have seen people simply run a 12 volt line directly tot he clutch lead. Remember that if you do this, you will not "cycle" the A/C system and the compressor will run non stop.

[onecrazyfoo4u]

Okay, I'll jump the low side switch again to see if the compressor kicks on. I don't think it will though, since it's only getting 4.7V all the time, right?

 

Where is high side switch connector located? Should the compressor turn on if I jump that connector as well?

[muddkatt]

Pretty sure the high side switch is built into the compressor and is the connector that is on the rear of the compressor. The clutch connector is at the front of the compressor right behind the clutch and is pointing down

[onecrazyfoo4u]

Pretty sure the high side switch is built into the compressor and is the connector that is on the rear of the compressor. The clutch connector is at the front of the compressor right behind the clutch and is pointing down

 

The clutch connector I checked voltage on plugs in at the bottom of the compressor. That line runs to the plugin at the back of the clutch compressor pulley. If I unplug and jump that switch, I don't think anything will happen because it won't be hooked up to any power lines. I didn't see any other wires running to the compressor unless I'm missing something. Here's a pic that shows what I'm talking about.

 

http://ecx.images-amazon.com/images/I/41l2Cqo6ZeL._SX425_.jpg

[muddkatt]

 

Purple connection is the high side ( I think) the connector in your photo and in mine that is near the clutch is where 12V should be, do NOT try and jump that connection.

[muddkatt]

Your truck might not have that connector since it is 4 years newer than mine.

[onecrazyfoo4u]

Oh cool thanks, I'll inspect the back better tonight. I leave the drier and clutch connections both hooked up, then try jumping the switch on the back of the compressor. This time do I jump the connector that goes in to the purple switch? Or do I jump the purple switch itself?

[muddkatt]

Jump the connector and test for voltage at the connector for the clutch.

[onecrazyfoo4u]

Sorry, I'm stupid when it comes to HVAC stuff. If I disconnect and jump at the clutch connector wiring, then how would the compressor ever start if it's not hooked up to any power? Or is it getting power from the purple connector switch?

 

When I checked voltage at the clutch connector switch, it was always getting 0 V.

[rjgti]

connector for clutch is black

[muddkatt]

Sorry, I'm stupid when it comes to HVAC stuff. If I disconnect and jump at the clutch connector wiring, then how would the compressor ever start if it's not hooked up to any power? Or is it getting power from the purple connector switch?

 

When I checked voltage at the clutch connector switch, it was always getting 0 V.

Lets start over.....

1. unplug the connector for the low side. It is located next to the cab on the dryer. It s the round thing about the size of a 24 oz beer can.

2. put a paper clip into both sides of the plug that you just removed.

3. locate the high side connector that is on the back side of MY compressor, your might be in a different location, I cant tell you where it is.

4. jump that connector with a paper clip.

5. Now unplug the clutch connector.

6. with the truck running, test the voltage. If you have no voltage, remove the paper clip from the high side and retest.

NOTE: all jumpers and test are on the wiring harness, NOT on the switches themselves.

[onecrazyfoo4u]

Awesome thanks. Sorry for my stupidity . On 6. when I remove the paperclip from the high side, do I plug the high side back into the connector before checking again?

 

And where exactly am I checking for voltage during all these steps? On the paperclips themselves? Or on the switches?

[muddkatt]

On 6, just test for voltage without plugging it back up.

 

During every step, test for voltage on the wiring harness connector that goes to the clutch. It is the other end of the black plug in the picture I posted.

 

What i am having you check is to see if something is wrong and causing your truck to not have voltage to the compressor. Once you eliminate the High side and low side switches, you will be able to narrow down the problem.