A/C Compressor clutch not engaging

Good morning,

The thermal fuse was a very bad idea and caused more issues than it solved.

I attached a wiring diagram for you of the A/C system. You need to go to the relay and test for 2 powers with the key on. The control side will ground and energize the relay when it sees the correct signal from the pressure sensor. The engine ECM controls that operation.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

https://www.2carpros.com/articles/how-to-use-a-voltmeter

The diode is part of the clutch in the compressor.

It looks like you may need to replace the compressor if you power there when the command from the control head.

https://www.2carpros.com/articles/replace-air-conditioner-compressor

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Roy

Roy,

Thanks for the reply and appreciate the speedy reply. Have family over this evening, may be a day or two before I can get back under the hood but truly appreciate the information and the diagrams. I will follow back up with my findings.

John

You are welcome.

Always glad to help.

Roy

Roy,

Not sure how this happened but may have been the result of using the thermal fuse. I'm picking one up today on the way home, hope to get it replaced and then I'll be checking the lines with the diagrams you provided. Photo attached of the plug on the compressor.

I also updated my description to give you a bit of background as well.

John

That is one corroded connector. Clean up the terminals.

Roy

Roy,

The picture of the connector, while there may be some corrosion there, the biggest damage is, it's melted and may not allow for proper mating but I'll get to that after I confirm the wiring diagram first.

On the diagram, A/C Compressor Clutch Relay, IGN E fuse 10A, not finding it. I see the relay and the A/C compressor fuse but not the IGN E fuse. I'm attaching a diagram from under the cover and maybe I'm overlooking it?

On the A/C compressor fuse, I do have 12 .5 VDC on the one side. I just need to find the other fuse, unless it's labeled different?

I'm also attaching a picture with me pointing at what I think is the under hood engine control module, on the left front side of the engine compartment, next to the battery and fuse box?

John

Never mind, found the fuse. I'll let you know...

Keep me updated.

Roy

Roy,

Okay, tested for the 12~14 volts on the two fuses. Present. I'll have to check next if the voltage is getting to the plug at the clutch.

Am I to understand that when the ECM detects the signal that the A/C in the cab has been turned on, it supplies the ground to the relay so that it will engage the clutch?

It'll be tomorrow before I can get back under the truck and do a voltage check at the plug to see if it is present.

And another question. Is it possible the compressor is still functioning but the clutch is failing?

John

Yes, once the ECM sees the correct signal from the pressure sensor, it will ground the control side of the relay and energize the relay sending power to the compressor.

Roy

Roy,

Got under the truck and disconnected the plug at the compressor. Had my wife crank the truck and turn the AC on. I put a meter on the green wire and to ground, reading was 0 vdc. Both fuses were still intact. I even replace the relay to no avail. I haven't tested the slots on the relay yet. Working on getting test clips and use something like a paler clip to make sure the voltage is there when the AC is turned on so it should energize the relay like it should. I'd the voltage is there to energize the relay then the control module is doing it's job. My other thought is, if the switch in the cab isn't working to send the proper signal to the ECM, then it (the fan or AC engage switch. Not sure of the exact name but the snowflake switch) could be the culprit.

I'm going to create a wire long enough to reach my meter and perform a continuity check between the plug on the compressor (green wire) to pin 87 on the relay and make sure that wire hasn't melted somewhere along the mix.

Your thoughts.

John

Go to the relay and with the key on there should be 2 powers, one at 86 and one at 30.

If there is then it sounds like the control side is not being grounded.

Did you check the freon pressures as I suggested?

Roy

Roy,

I looked back and didn't see any reference to checking any pressures either low or high but I've overlooked things before.

I will see about getting a gauge on there and checking the pressures.

I remember a former test where you can jumper the plug at the low pressure side to engage the clutch but don't remember the procedure. That was done a few months back and it passed then but things can change.

I'll let you know what the pressures are once I get my hands on a pressure gauge.

John

Sounds good.

Roy

Roy,

I put the gauge on there but not sure what is a good reading. Photo attached.

I also checked to see if the relay was engaging when the air was turned on in the cab. The relay did click when I turned on the air.

John

Okay, did the compressor come on? Those readings with the compressor on indicate a bad compressor. It is not producing any pressure.

https://www.2carpros.com/articles/replace-air-conditioner-compressor

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

I attached the procedure for you for the compressor below.

Roy

Roy,

No, while the relay did click, the compressor did not turn on. I do have a replacement plug. That'll go in this afternoon after I get home, out in errands.

John

Sounds like a plan.

Roy

Roy,

Finally got back under the hood. I tested for continuity from the compressor to relay contact 87. 0 ohms.

From the 10 amp A/C compressor fuse to pin 30. Infinity. That explains why the compressor wasn't kicking in. So, instead of replacing the fuse box or trying to dismantle the fuse box, I ran a 16 gauge jumper from the fuse to pin 30. Picture attached.

Compressor kicked in, cycled twice and then nothing. Checked the fuse, still good. Snapped a picture of the gauges while the clutch was engaged but that doesn't look like it's right. That picture attached as well.

John

The static pressure is not bad. What happened to the low side pressure when the compressor kicked on?

Roy

It initially went down but looking at that gauge, it looks like it krept back up by the time the picture was taken.

Just adding some freon and see if the compressor stays on. Below 20 pounds on the low side, it will not stay engaged.

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

Roy

Roy,

Time and proper tooling was my enemy.

I narrowed it down to one, what you mentioned about the low pressure, not allowing the clutch to remain engaged and two, I wasn't getting a proper signal from the fuse/relay to the compressor.

After going over many techs in my area, I picked the one I thought would serve the purpose and took the truck down to him yesterday. He found what was suspected. I didn't have any way to properly evacuate and then replace the Freon in the system. That was the first thing he did. Then he found the signal not getting to the compressor as I had found. Somewhere in the harness, there is a short with that line. He bypassed it by running a wire from the fuse box to the compressor and solved the issue. I am back in business and the A/C is working as it should. Clutch and compressor are fine and all is well.

What will still be in the back of my mind is, where is the short. Not to hard to imagine because I do live down a dirt road with a few dips here and there. Maybe next on my list needs to be a new set of shocks.

Thanks for the assist and stay safe.

John

Good deal. The issue with the short will always be there. Rarely is there just 1 wire damaged. There is usually more than 1 wire all the time.

I would have suggested tracking it down and repairing it correctly rather than doing a wire overlay as he did.

You are welcome.

Roy

I am going to stop by there today and ask more information on where he tapped into and see where the actual line goes. I had read where this is not the first of it's kind and with this specific line. Apparently repeated in same models, occurring somewhere the line travels from the compressor around the transmission housing on to the fuse box.

Agreed, there has to be a cluster of wires and more are probably on the verge if not already shorted.

Thanks for all of your help.

John

You are welcome.

Always glad to help.

Roy