A/C Compressor Clutch - Diagnosing

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GordDavey

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Hi All, I'm having a problem with the A/C in my 2015 Ram 1500. As it was rebuilt after an accident, I highly doubt any warranty would be valid, that being said I have 1 issue left to resolve with the truck, my A/C not working.

My professional mechanic is also a licensed A/C guy, but has never dealt with the Variable Displacement A/C compressors that are now standard for our trucks. He's dealt with the refrigerant R1234yf, but not the A/C compressor itself, so I have a few questions.

The issue is the A/C clutch will NOT engage. I am trying to find a way to diagnose the clutch issue manually. There are 2 connectors for the A/C compressor, the C1 connector at the top and front, and the C2 connector under and towards the back. We have no idea if there are electronic circuits inside the compressor itself for it to make any of it's own decisions, we figure not and that the ECM and HVAC module make all the decisions. I need to figure out for sure if the compressor/compressor clutch is bad before making the massive investment to discharge, replace the compressor unit and recharge it. (like 2000+ CDN)

I imagine C1 connector controls the compressor clutch engagement and C2 controls the swag(?) angle, but I need this confirmed.

What voltage would be measured across the C1 connector to know it is receiving the correct power?
What the resistance should be when measuring across the 2 pins on the compressor itself (C1 disconnected from compressor, and resistance from the compressor itself and not from the engine harness.)

What voltage would be measured across the C2 connector's body harness side?
What resistance would the compressor side of the C2 connection should be?

Is there a way to manually check the compressor's clutch engagement? The old fixed displacement A/C compressors you could just apply battery power to them, and it would engage and disengage, but we're unsure with the variable type. Does the engine need to be running to manually test the clutch engagement? or can you just supply battery power to it and it would toggle on and off like the old style did?

Any info/help would be much appreciated.
 

Nick_rp

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If your A/C system was damaged and your car insurance paid for the fix, usually they have a parts guarantee but you have to call your insurance to have the process started.

I did that recently my self. Insurance replaced my headlight housing and most of the mounting tabs had broken in about 3 months. Guessing it was a cheap knock off, so my insurance got it replaced again.
 

alpinegreenneon

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Can you check resistance for the clutch solenoid at the compressor where C1 connects? Resistance should be low. If it's infinite, there is an open. You could also swap the AC clutch relay in the PDC with a same type relay as a test. If you have a spare relay, remove the cover and squeeze the contacts together manually. Did you check the fuse?
 
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GordDavey

GordDavey

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If your A/C system was damaged and your car insurance paid for the fix, usually they have a parts guarantee but you have to call your insurance to have the process started.

I did that recently my self. Insurance replaced my headlight housing and most of the mounting tabs had broken in about 3 months. Guessing it was a cheap knock off, so my insurance got it replaced again.
Nick_rp,

We purchased the truck as a write off from insurance and have rebuilt it. The damage did not touch the engine. But it was a front end collision.
 
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GordDavey

GordDavey

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Can you check resistance for the clutch solenoid at the compressor where C1 connects? Resistance should be low. If it's infinite, there is an open. You could also swap the AC clutch relay in the PDC with a same type relay as a test. If you have a spare relay, remove the cover and squeeze the contacts together manually. Did you check the fuse?
Alpinegreenneon,

I’ve got power at fuse 62. I’ve got power when I put a voltmeter on the C1 connector and C2 connector (both 12v+) coming from the engine harness. At the C1 on the compressor I measure 5ohms and 10.9ohms at the C2. But I don’t know if these values are correct or not.

A bit of back story. During the rebuild the BCM and wiring near it got burnt. We replaced the BCM and wiring and got the truck flashed. The wiring came from a 2014. We changed the body harness and the dash harness. The 2014 supposedly had an 8.4 with single zone bezel mine was originally the 3 knob manual. But we could not get power at fuse 62. I checked the wiring at the hvac module and it matched a dual zone not a single zone wiring diagram. When I set the BCM to dual zone. I got power at fuse 62 and the AC started working but stopped the next day. The compressor has worked a couple of times in the past, very few times mind you. Because it has worked in the past my mechanic can’t get past the wiring. But I’m get power measured at both plugs now so I think it may be a bad/intermittent connection in the AC clutch. But I’d like to find a way to prove it especially considering the cost. Basically the wiring has saved me from turning the old single zone into dual zone ATC. It is all functioning perfectly except the AC compressor.
 
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Tach_tech

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There is an electronic controlled solenoid in the compressor. It is what varies the displacement of the compressor.

Connector C1 should have 12V and ground. C2 will have ground and a pulse width modulated circuit. How much voltage there will be on the circuit depends on demand of the system.
 
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GordDavey

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Tach_tech,

Thank you. So, if I just put battery power and ground to the C1, should I see the clutch engage and disengage? Does the truck need to be running for me to try that?

C2 having 12v on it, must mean that it is calling for 100% on the solenoid then, since as you say the voltage will vary with the demand.

The electronic controlled solenoid does it look at anything other than the incoming power on C2? Meaning is there any sort of pressure sensor in the AC Compressor or some other bit of electronics checking something? I'm trying to figure out if there is ANYTHING else that will influence the A/C clutch engaging or not engaging other than just the voltage on C1.
 

Tach_tech

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C1 receives power from the clutch relay. If the relay is engaged you should have power at fuse 62 and at the blue/yellow wire of C1. You should have a constant ground signal on the black wires of both C1 and C2. If there’s no ground, there’s an issue.

The HVAC module is what sends the PWM signal to the solenoid inside the compressor. The solenoid doesn’t control itself, it is directly controlled by the HVAC module.

So if you have power/ground at C1 and C2 but you have no pressure being built by the compressor or the clutch isn’t engaging then it’s a compressor/clutch issue.

Are you sure the system is fully charged? If it’s not the A/C clutch relay isn’t going to engage.
 
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GordDavey

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Tach_tech,

I don't know what the final pressures were when it was charged. But I was told last night he had to jump the C1 to the battery to get it to work so he could finish charging the system... We ran out of time to diagnose the AC and I had to drive the truck 3000 miles home, and I've been checking and trying various things since then, and I'm down to either the AC clutch is good or bad at this point.

I did build a little harness to go between the AC Pressure Transducer and it's connector, so I could put a voltmeter on the pressure switches ground and signal wire and I'm getting 0.78 volts from it, which from what I've read means 78 psi, and that is without the compressor clutch engaged ('cause it won't). If that is a good pressure when there is no compressor working I do not know.

I'm reading 12v at each of the C1 and C2 connectors when I set the system to max AC. So to me that would mean there is a good ground for each otherwise I shouldn't get anything, and if there is power there, then the Relay should be fine. I've verified that there is power at fuse 62... on both sides of the fuse. But I've never touched the AC Clutch Relay, I only realized there was such a thing when I was reading this weekend. So I know nothing and have tried nothing with it to date. It sounds like the AC Clutch Relay is inline before the fuse, so with power at the fuse then the relay would be OK. If it comes after the fuse, then it is something I will need to check.

I'll have to try connecting C1 directly to the battery and see if it engages or not, beyond that I'll triple check the wires and the voltages at C1 and C2, if all that is what I think it is, then it must be a fault in the AC Clutch itself. As it has worked a couple of times in the past, perhaps there is a bad connection inside for the AC clutch itself.
 

Tach_tech

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If you have power at both connectors, you just need to check that there is ground. 12V on the power circuit doesn’t mean the ground is good.

To check the ground you can use a test light or multimeter.

For a test light, connect the clip to the battery positive post then use the test light on each ground circuit. The test light will light if there is ground. Make sure the connector is disconnected and you’re checking on the body side of the connector.

For a multimeter, set the meter to measure continuity and check from the ground at the connector to battery ground.

For the pressure transducer you can jump the two pins on the body side connector to test it. If everything else is in working order when you jump the switch the A/C clutch should engage.
 
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GordDavey

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Tach_tech,

Thanks I will give all of this a try this weekend, and see what happens.
 
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GordDavey

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Tach_tech and alpinegreenneon,

I cannot thank you two enough... I have working A/C now without the big expense.

I ran some wires from the C1 connector on the compressor to the battery, and the A/C clutch engaged and disengaged properly whenever I applied power, so I knew it was fine.

I then checked the C1 and C2 connectors, and sure enough there was no ground continuity on the C1 ground wire. Since it was a nasty place to get up close and personal with the wires, I removed the front wheel and wheel well liner. Stripped off the tape and the plastic loom, and found a small pinched point in the ground wire, removed a bit of insulation above that and had a good ground there. So I cut out that bit, some solder and heat-shrink, and checked continuity and had a good ground at the connector. Put it back together and checked the A/C function, gave a big loud "Wahoo", it all works great. Re-wrapped and put everything back together. Thanks to you guys I knew how to diagnose it properly and what I should expect, thanks so much for the wisdom.
 

Rafael Blanco

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Hey guys I am new here!
I bought a 2014 Ram couple of weeks ago and the A/C has only worked twice. My case is similar to the one described here I and had fuse 62 blown once. I did replace it and check for power coming into the fuse with the AC controls set to full blast there is not voltage. I look at the repair manual and it shows an AC clutch relay before the fuse but there is no AC relay in the power distribution center. any ideas? I do not want to put direct voltage to the coil as I am afraid to burn it up but before I suspect the clutch to be bad I need to see voltage going to it and at the moment I am not getting it.
Thanks in advance!
 
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GordDavey

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Hey guys I am new here!
I bought a 2014 Ram couple of weeks ago and the A/C has only worked twice. My case is similar to the one described here I and had fuse 62 blown once. I did replace it and check for power coming into the fuse with the AC controls set to full blast there is not voltage. I look at the repair manual and it shows an AC clutch relay before the fuse but there is no AC relay in the power distribution center. any ideas? I do not want to put direct voltage to the coil as I am afraid to burn it up but before I suspect the clutch to be bad I need to see voltage going to it and at the moment I am not getting it.
Thanks in advance!
Let me know if your truck is Gas or Diesel (engine size too), and what type of Heating System you have (manual or automatic). I have the 2014 wiring diagram, and while the A/C is basically the same for all the different types, there are differences in wire colors. I can send you a piece of the wiring diagram dealing with the A/C.
The A/C clutch itself has two wires, ground and power. You can disconnect the clutch wire and jump them to ground and power at the battery. You won't hurt it, its designed to take 12v. Put the ground on, then touch the power wire to positive on the battery and you should see the clutch move in and out. If it doesn't move, double check your connections, if it still doesn't move then the clutch is bad. If it does move properly, then you can trace it further.

The Relay they refer to is built into the circuit board in the PDC and cannot be replaced separately as far as I know.

The heater module, which depending on the heating type (manual or automatic) will either be a small back box at the far right side of the dash behind the right end dash panel, or will be part of the heating circuit on the back of the controls in the center console (manual). It has a wire which which goes to the A/C clutch should be Light Blue with a White stripe, this wire simply sends 12v when the heating module wants the AC Clutch to engage.

The engine computer (PCM) deals with the AC Compressor control, that wire goes from the PCM to the PDC (fuse box) to supply power to the relay which is part of the circuit board in the PDC. Power comes out the relay thru fuse 62 and down to the back of the AC Compressor, you should get 12v at the AC Compress connector when the truck wants the AC to run. If you get 12v on the Dark Blue with Yellow stripe wire on the back of the AC Compressor when the truck calls for the AC to be on, then it is OK.

You should ensure both black wires in the AC Compressor and AC Clutch connectors get a good ground. Make sure the AC is on and check the power wires for 12v and see which is not right. Depending on what you get, it will point to what the problem is. For the AC Clutch it will be one of: a bad clutch, or a bad power wire or a bad ground or a bad heater module. If the problem is the AC Compressor values, then it could be a bad compressor, bad PCM, bad PDC or power / ground wiring.
 

Rafael Blanco

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Thanks!
It is a 5.7 with the manual HVAC system. I will check the voltages to the coil connector tomorrow and I will try to power up the coil directly and report back. I hope is not a bank braking issue.
 

Rafael Blanco

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OK,
I tested the coil and it works, it latches on easily. Still the is not power to the it when the AC know is on and voltage is 0 at fuse 62 (clutch). what else do I check? How do I keep tracing the problem? Could it be he compressor solenoid?
Thanks for any help you can provide.
 
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GordDavey

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OK,
I tested the coil and it works, it latches on easily. Still the is not power to the it when the AC know is on and voltage is 0 at fuse 62 (clutch). what else do I check? How do I keep tracing the problem? Could it be he compressor solenoid?
Thanks for any help you can provide.
Rafael. So, the clutch works when you jump it to the battery. Fuse 62. Are you sure you are getting zero volts out of both sides of the fuse? Put your voltmeter on the battery negative terminal and the positive to both sides of the fuse. If you get 12v on one side, then the fuse is blown. If you get 0v on both sides, then you need to track down why you are getting 0v to the AC Clutch.

The AC Clutch wire goes from the AC clutch up to pin 9 connector 3 of the PDC (fuse box) Connector 3 is the ********* one under the fuse box, you should be able to see an indicator on the plastic for pin 1, you are looking for pin 9 which should have a Dark Blue with Yellow Stripe wire.

AC 2014.jpg
 
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GordDavey

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OK,
I tested the coil and it works, it latches on easily. Still the is not power to the it when the AC know is on and voltage is 0 at fuse 62 (clutch). what else do I check? How do I keep tracing the problem? Could it be he compressor solenoid?
Thanks for any help you can provide.
There is a clutch control wire in the (Module PowerTrain control) (typically I call it ECM for Engine Computer), a wire Light Blue and Orange goes from connector C1 (Black) pin 79 on the ECM to the Fuse box (PDC) Connector 3 (black) pin 10.

The A/C Pressure Transducer is also part of the Clutch Control circuit, its a smallish sensor in the AC tubing not far from the fill openings. It has 3 wires, ground, 5v and pressure signal. You can put a voltmeter to ground and the pressure signal and you can see how much pressure it is sending, 1v=100psi, 1.5=150psi, 5v=500psi. This sensor can be replaced without draining the system.

So, if your A/C Pressure is too low or the sensor is bad, then the ECM will not allow the clutch to get voltage, which means 0v at fuse 62.
 

Rafael Blanco

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Thanks Gord,
both ends of the fuse have 0v and I even put a new fuse just to be sure. I will try to check the pressure transducer tomorrow. I did connect the gauges and the low pressure was on 60psi and the high pressure was 20psi with the clutch disengage. I am not sure if that is OK but at least I know there is freon in the system. what voltage should I get from testing the pressure transducer to be correct? Where do I go if the pressure transducer checks OK?
Thanks.
 
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