2002 Silverado A/C clutch won't engage

[Eagle70ss]

So here's the story....My compressor sounded a little noisy so I decided to do a a/c system evac...I also drained the compressor oil and replaced it with new oil. Put a new orifice tube in there as well.

I went to recharge the system and I noticed the a/c clutch will not engage. So I jumpered the low pressure switch on the accumulator and the clutch still didn't engage.

The only way I can get the clutch to engage now is to jumper the relay pins at the fuse box. When I manually engage the clutch at the relay pins, the clutch engages fine and the air inside the cab is blowing cold.

However as soon as I remove the jumper wire, the clutch shuts off and will not turn back on....

Where should I start looking next?? Switch on the back of the compressor?

[brcidd]

Did you try swapping the relay with the horn relay? I've seen bad connections on relay legs cause same issue- wiggle relay. Also see if the ecm is grounding the negative relay coil- by using your volt/ohm meter. If not, then look at pressure transducer input (high side line)- or switch on back of compressor- depending on application.

[Eagle70ss]

Originally Posted by brcidd

Did you try swapping the relay with the horn relay? I've seen bad connections on relay legs cause same issue- wiggle relay. Also see if the ecm is grounding the negative relay coil- by using your volt/ohm meter. If not, then look at pressure transducer input (high side line)- or switch on back of compressor- depending on application.

I did try and swap the horn relay and still no clutch...I'm unsure how to check the negative relay coil with my volt meter?...I suppose I'll try to jumper my connector on the compressor switch to see if clutch works...

[brcidd]

The compressor switch is normally closed- opens at high pressure. Is your a/c indicator on control head on-- some of those trucks have reverse logic-- the switch lite is on when NO a/c is requested --ie; it has a slash through the a/c command button. Do you have automatic or manual controls?

[l1driver]

Had the same.issue on my 00 Silverado]. Turned out to be clutch coil. Cost $100 for new coil and a couple hours labor. Did it myself with the help of a AC clutch puller I rented from Auto Zone.

[Eagle70ss]

Originally Posted by brcidd

The compressor switch is normally closed- opens at high pressure. Is your a/c indicator on control head on-- some of those trucks have reverse logic-- the switch lite is on when NO a/c is requested --ie; it has a slash through the a/c command button. Do you have automatic or manual controls?

I have manual temp controls. The A/c indicator light activates as usual when I press the A/c button on the controls.

So today I jumpered the connector on both the low pressure switch and high pressure switch and still no clutch.

I attached a pic of my a/c control module...

[j cAT]

Originally Posted by Eagle70ss

I have manual temp controls. The A/c indicator light activates as usual when I press the A/c button on the controls.

So today I jumpered the connector on both the low pressure switch and high pressure switch and still no clutch.

I attached a pic of my a/c control module...

the power to the clutch coil has a fuse. the relay coil has / uses a different fuse. if the ac compressoor clutch relay coil fuse is blown this is what will occur.

check all fuses. should be a 10amp.

[Eagle70ss]

Originally Posted by j cAT

the power to the clutch coil has a fuse. the relay coil has / uses a different fuse. if the ac compressoor clutch relay coil fuse is blown this is what will occur.

check all fuses. should be a 10amp.

Checked all fuses and all of them are good. I'm getting power to both relay pins that should have it ( 30 & 86)...I can start the clutch by jumpering either (30 to 87) or (86 to 87)...

So I'm guessing that I'm not getting the ground provided by the PCM to pin 85 to complete the relay circuit?

[j cAT]

Originally Posted by Eagle70ss

Checked all fuses and all of them are good. I'm getting power to both relay pins that should have it ( 30 & 86)...I can start the clutch by jumpering either (30 to 87) or (86 to 87)...

So I'm guessing that I'm not getting the ground provided by the PCM to pin 85 to complete the relay circuit?

ground out relay pin 85 . this should get the clutch to pull in . if so then check hvac 1 fuse and also see that the high pressure switch has about 5 volts on both pins. then check that low pressure sw is grounded/going to ground.

if all this checks out good then what would prevent the clutch to pull in would be an error from the engine management like an over heating or other operating report causing this not to operate.

the pcm or connectors need inspecting / broken wires

[Eagle70ss]

Originally Posted by j cAT

ground out relay pin 85 . this should get the clutch to pull in . if so then check hvac 1 fuse and also see that the high pressure switch has about 5 volts on both pins. then check that low pressure sw is grounded/going to ground.

if all this checks out good then what would prevent the clutch to pull in would be an error from the engine management like an over heating or other operating report causing this not to operate.

the pcm or connectors need inspecting / broken wires

So I put pin 85 to ground while relay was still in and it pulls the clutch in each time I put 85 to frame. All hvac fuses are good. I wasn't able to get a reading on the high switch for voltage because I don't have a lift and the compressor is in a dumb place. I miss my ol' 95 chevy where the compressor is right on top.

However, I pulled the connector off of the high switch(engine off) and I put my meter across the two connector pins and I get a constant .3 ohms across the pins. This mean I have good continuity?

Then, I do the same for the low pressure switch connector and at first I get no constant reading. So I move further down the wires and I pierce into each wire with the meter leads. I get a stable reading of something like 20 Meg ohms...? Should the resistance be this high at the low pressure connector? Should I get about the same resistance as the high switch connector?

Thanks

[brcidd]

That high pressure "switch" down low is NOT a switch-- if it is 3 -wire- it is a pressure transducer- that constantly monitors a/c high side pressure- don't jumper it- you could hurt the PCM- instead make sure one wire is ground, another has 5 volt constant and the third varies 0-5 volt with a/c system pressure- I don't have the wire colors in front of me.

[j cAT]

Originally Posted by Eagle70ss

So I put pin 85 to ground while relay was still in and it pulls the clutch in each time I put 85 to frame. All hvac fuses are good. I wasn't able to get a reading on the high switch for voltage because I don't have a lift and the compressor is in a dumb place. I miss my ol' 95 chevy where the compressor is right on top.

However, I pulled the connector off of the high switch(engine off) and I put my meter across the two connector pins and I get a constant .3 ohms across the pins. This mean I have good continuity?

Then, I do the same for the low pressure switch connector and at first I get no constant reading. So I move further down the wires and I pierce into each wire with the meter leads. I get a stable reading of something like 20 Meg ohms...? Should the resistance be this high at the low pressure connector? Should I get about the same resistance as the high switch connector?

Thanks

the high pressure sw is always closed if normal pressure. its a safety. pressures too high it will open causing PCM to shut down the clutch . .3 ohms sounds good at the compressor sw. this provides a feed signal to the pcm from the hvac controller.

the low pressure sw should be grounded with a pressure of more than 5 psi approx. this is to protect the compressor fron lack of refrigerent/oil . this is usually what goes wrong as it is working all the time .

by grounding out the #85 pin this is bypassing the pcm control .

so the low pressure sw not going to ground would be a cause of you issue. the low pressure sw should be closed a short circuit very low ohms . 0- .5 ohms .....also measure to ground same reading. this is with the connector on. as one wire goes to ground the other goes to the pcm. if these wires are open or one not going to ground this is another reason.