Jump AC compressor

[adamj]

The AC is not working and I'm trying to track it down and get it up and running again.

The compressor clutch is not engaging. I think there's a leak somewhere, and I'm going to address that, but I want to make sure the compressor is working first. I charged the system a bit, but the compressor did not kick on. I jumped the pressure sensor by the accumulator, and now rpms go up slightly when ac is switched on and back down when switched off. I reconnected the switch properly, pressure must have built up so it still has rmp change when ac selected. After a few days, this stopped working, must have lost pressure through a leak or something.

I want to check if the compressor is working or not. I know dark green is power, black is ground. If I apply a 12V power to the connections, I should see compressor engage. But I don't know which terminal is which? Looking from the front, which one is power and which is ground? I have a 12 oclock clocking for the connector.



yes, i know it's winter and we just got 2" of snow last night, but I want the ac to be working for defog ability.

The plan:
Once I can get the compressor running (hopefully) then I will do a full recharge, find out where the leak is with UV dye, and make sure no other components are damaged. Then, have a shop do an environmentally-sound discharge, and also a system flush.
Probably have to replace compressor.
Reconnect everything, new o-ring kit, oil, and recharge system.
Down about $125 for discharge and flushing, ~$200 for R4 compressor.

 

[chengny]

I jumped the pressure sensor by the accumulator, and now rpms go up slightly when ac is switched on and back down when switched off.

That's right. With the low pressure control switch jumped - and any A/C setting selected on the control panel - you are supplying power to both the compressor clutch and the ECM. The signal to the ECM tells it - that because the AC compressor clutch is now engaged - to artificially increase the engine RPM.

So you know that there is power coming from the control panel to the control switch, through the jumped out control switch and over to the compressor/ECM split.

The ECM is reacting as designed, but the clutch is not pulling in.

That would indicate that there is an issue with one of the following:

1. The compressor clutch itself

2. The wiring from ECM/compressor splice point

Like this:

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To diagnose which problem you have, check for power to the clutch at the compressor harness plug (with the AC turned on and the control switch jumped out).

If power is available at the harness connector and the clutch does not engage, make sure you have a good path to ground on the other side of the plug.

If you have a good ground and 12 VDC at the harness connector - the clutch is NG.

No power at the plug - check the wiring from the splice to the compressor.

No continuity to ground on the other side of the harness plug - run a new wire or repair the old one.

 

[adamj]

I jumped the pressure sensor by the accumulator, and now rpms go up slightly when ac is switched on and back down when switched off.

That's right. With the low pressure control switch jumped - and any A/C setting selected on the control panel - you are supplying power to both the compressor clutch and the ECM. The signal to the ECM tells it - that because the AC compressor clutch is now engaged - to artificially increase the engine RPM.

So you know that there is power coming from the control panel to the control switch, through the jumped out control switch and over to the compressor/ECM split.

The ECM is reacting as designed, but the clutch is not pulling in.

That would indicate that there is an issue with one of the following:

1. The compressor clutch itself

2. The wiring from ECM/compressor splice point

Like this:

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To diagnose which problem you have, check for power to the clutch at the compressor harness plug (with the AC turned on and the control switch jumped out).

If power is available at the harness connector and the clutch does not engage, make sure you have a good path to ground on the other side of the plug.

If you have a good ground and 12 VDC at the harness connector - the clutch is NG.

No power at the plug - check the wiring from the splice to the compressor.

No continuity to ground on the other side of the harness plug - run a new wire or repair the old one.

Control switch jumped, I'm getting 12V, and still no compressor engagement. I guess the compressor is shot... (well the clutch anyways). I even tried applying 12V to the compressor directly, and nothing happened, no click, nothing.
Time for a new compressor, but which one to get? Is there a larger capacity compressor needed for the dual system (with rear A/C)?

 

[chengny]

Because you have eliminated a no/low voltage condition - by using a jumper to the battery positive, that leaves two possible (electrical) causes for the coil failing to pull the clutch in. It could be due to the lack of a sufficient ground or an open in the coil windings.

You've most likely done this already, but just in case:

Pull the connector and check for continuity to ground on the black wire.

BTW - You didn't ask but, polarity doesn't affect an electromagnet. So it doesn't matter which way the leads are connected to the coil terminals.

If you get a good path to ground through the black wire, check the resistance across the coil windings. Ideally the resistance should be 3.85 ohms for an A-6 clutch coil. But if you get anything above 2 ohms (and not much over 15 ohms) it is acceptable.

Under 2 ohms - the coil windings are shorted internally

Over 5 ohms the coil is open (infinite resistance) or the copper windings are damaged (high, but not infinite).

If both those checks give good results, you might want to check for mechanical issue - like the clutch plate binding.


One more thing, if you do have an A-6 compressor, you might want to check the back end where the hose manifold bolts on. A-6 comps often have a superheat switch in the ground circuit. If it has tripped, you will get a good reading at the harness connector and show an open in the coil windings.

 

[adamj]

Because you have eliminated a no/low voltage condition - by using a jumper to the battery positive, that leaves two possible (electrical) causes for the coil failing to pull the clutch in. It could be due to the lack of a sufficient ground or an open in the coil windings.

You've most likely done this already, but just in case:

Pull the connector and check for continuity to ground on the black wire.

BTW - You didn't ask but, polarity doesn't affect an electromagnet. So it doesn't matter which way the leads are connected to the coil terminals.

If you get a good path to ground through the black wire, check the resistance across the coil windings. Ideally the resistance should be 3.85 ohms for an A-6 clutch coil. But if you get anything above 2 ohms (and not much over 15 ohms) it is acceptable.

Under 2 ohms - the coil windings are shorted internally

Over 5 ohms the coil is open (infinite resistance) or the copper windings are damaged (high, but not infinite).

If both those checks give good results, you might want to check for mechanical issue - like the clutch plate binding.


One more thing, if you do have an A-6 compressor, you might want to check the back end where the hose manifold bolts on. A-6 comps often have a superheat switch in the ground circuit. If it has tripped, you will get a good reading at the harness connector and show an open in the coil windings.

Thanks Chengny, I have not done this yet, and it is all very valuable information for me, so thanks for commenting! I will get that multimeter back out and see what's up. However, I believe I have an R4 compressor, but not sure, and if not, would it still have an overheat switch (I will check when I get home from work):

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[adamj]

1) I didn't see a switch on the back of the compressor, so I guess I don't have an A-6 comp.
2) I have full continuity to ground at the black ground wire.
3) Resistance across was 3.9 ohms (is this still a good reading for an R4 compressor?)

So mechanical issue now? Is this something I could fix myself? Or is it not worth it...

 

[chengny]

Yep, that's an R-4 compressor - I thought all Suburbans used the A-6 style. Wrong again.

Anyway, I agree. It appears from the tests you have done, that everything is okay with the clutch coil and it's wiring - electrically.

The thing is, there really isn't much involved - mechanically speaking - as far as getting the drive hub to pull in and engage the rotor.

The drive hub is the outermost plate and is supposed to be stationary - when the coil is de-energized. When power is applied to the the coil, the electro-magnetic force that it generates exerts an inward force on the drive hub. The only resistance to the inward pull is the outward force of the three spring arms:

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Those three arms aren't real strong. You should be able to push in on the hub plate at the spring buttons and easily make it come in contact with the drive face of the rotor. Maybe not all at once but at least one at a time:

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The rotor is driven by the belt and is always spinning:

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When the drive hub plate is pulled in, it engages the clutch face and the spinning force of the rotor is applied to the drive hub. The hub is splined or keyed to the compressor shaft. So when the hub engages the rotor, the compressor shaft begins rotating.


Without knowing anything of the history on this issue, I can't speculate as to why the clutch won't engage. The only thing that would normally prevent engagement would be if there was an excessive air gap. If the distance between the hub plate and the face of the rotor is too great, the pull from the coil doesn't extend far enough out to "grab" the hub plate and pull it in. But that excessive gap doesn't develop overnight. It happens slowly. And over a period of time, clutch engagement becomes more and more intermittent - until one day it just won't engage at all.

Check the air gap between the faces of the drive and driven plates. The manual shows .0020" with a maximum of .0035". Check the gap like this and do it in 3 evenly spaced places:

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If you find the air gap to be considerably out of spec, try giving the coil a little help and see if it can engage the clutch. With one terminal connected to the battery (with a jumper) and the other terminal connected to a good clean ground (also with a jumper), push in on the hub plate and see if it suddenly snaps in to the rotor.

If it does, the gap needs to be adjusted.

 

[adamj]

Chengy! You are the troubleshooting master!
I got my feeler gauge and went to the truck, but when I opened the hood, I quickly realized that was not going to be necessary...

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Look at that gap!

So I jumped the coil and pushed the clutch in and "click" - the hub plate snapped right up to the rotor!

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So I guess the next question is: how can I tighten that gap?

(I did a search and saw somebody on youtube push the clutch in manually with a stick, maybe that can hold me over for a while - I'll just engage the clutch manually)

 

[chengny]

You'll need both these tools - the first one is in Autozone's the Loan-a-tool program. You just pay the regular price and when you are done with it, you get your money back:

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The A/C clutch holding tool from OEM holds the compressor clutch in place when removing holding bolt by adjusting pins to fit holes in clutch. This tool prevents the clutch plate from turning when moving the shaft nut.
Holds compressor clutch in place when removing holding bolt
Adjust pins to fit holes in clutch

Part Number: 27000

Compatible A/C Compressors: GM R-4 Compressors, some GM, Pitts, and Ogura Clutches

Problem is, AZ has the hub puller (which you don't need) in their LAT program, but I don't think they have the install tool - and that is what you need to adjust the gap closer. It looks like this:

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That goes for like $20.

Advance sells this kit for $45.

http://shop.advanceautoparts.com/p/...P?zoneAssigned=1&prefStoredSet=1&prefZC=03064

IDK if there is even a pulley spanner included. You're going to have to work this out yourself. If you get the tools you should be able to figure out how to close the gap. I'm not exactly sure if the hub is moved in or the rotor is moved out. I have never used the install tool. I usually use big Channelocks for the spanner and pry it in/out or something.

Good luck.

 

[RustyPile]

Adamj started this thread almost 2 years ago and the last post was made a little over a year ago, so the information I have to add probably won't help Adamj. Hopefully, it will help others who have the same problem and are reading this thread.

The information given for adjusting the compressor clutch air gap is correct up to the last paragraph.. No offense chengny but the gap can be set/adjusted without moving the rotor. In fact, the belt can be left in place and under tension.. The gap spec chengny mentioned is for a new or reconditioned clutch plate and rotor.. Because of the uneven wear, I "shoot" for around .010" -- .025" gap.. My method for setting/adjusting the air gap is a "one shot" procedure.. No guesswork involved. In the case of the OP's compressor, measure the gap before removing the clutch plate. Subtract .010" from that and write the answer down for future reference.. Remove the nut on the end of the compressor shaft and use the aforementioned removal tool to remove the clutch plate.. On the shaft down deep in the cavity is a stack of shims (they look like washers) sitting on the shaft's shoulder.. Remove those shims (I use a pencil magnet) and measure the thickness of the shim stack.. Remove some shims whose total thickness is the dimension that was written down previously.. Replace the remaining shims and use the aforementioned install tool to reinstall the clutch plate.. Tighten the nut to about 18 ft lbs and you're done.. The gap will be perfect..

 

[eric 87]

Adamj started this thread almost 2 years ago and the last post was made a little over a year ago, so the information I have to add probably won't help Adamj. Hopefully, it will help others who have the same problem and are reading this thread.

The information given for adjusting the compressor clutch air gap is correct up to the last paragraph.. No offense chengny but the gap can be set/adjusted without moving the rotor. In fact, the belt can be left in place and under tension.. The gap spec chengny mentioned is for a new or reconditioned clutch plate and rotor.. Because of the uneven wear, I "shoot" for around .010" -- .025" gap.. My method for setting/adjusting the air gap is a "one shot" procedure.. No guesswork involved. In the case of the OP's compressor, measure the gap before removing the clutch plate. Subtract .010" from that and write the answer down for future reference.. Remove the nut on the end of the compressor shaft and use the aforementioned removal tool to remove the clutch plate.. On the shaft down deep in the cavity is a stack of shims (they look like washers) sitting on the shaft's shoulder.. Remove those shims (I use a pencil magnet) and measure the thickness of the shim stack.. Remove some shims whose total thickness is the dimension that was written down previously.. Replace the remaining shims and use the aforementioned install tool to reinstall the clutch plate.. Tighten the nut to about 18 ft lbs and you're done.. The gap will be perfect..

I read this entire thread hoping to find something I can use with my 69 firebird with an A6. I doubt anyone else is reading this thread to the end now though but what the heck I will try. I have an 87 GMC sierra 305TBI or was. It is now 305 CARB. I know I know don't do it etc.
But I was wondering about the AC. Is it running through the ECM. If I get this truck back together after this TBI to carb swap and it runs good....I will drop tanks and change sending units. I will use an electric fuel pump with low pressure. I may keep the regulator I am using with this swap currently to err on the safe pressure side.
But then I will order a complete wiring harness. Reason is that I know this stock 305 will give up sooner than later. All the parts I am using for this swap will work on a long block replacement.
Older trucks had AC so I know there is a way to run AC wiring without an ECM and the fuel system as well. I think I know how to do the fuel system now and still use the dash switch. But the AC I am not sure about AND I think the cruise control is Vacuum controlled and have to figure that one out as well.
So for this thread how to wire the AC without use of the ECM.
Any help would be great. Long shot I am sure since I am doing this now.

 

[AuroraGirl]

your truck,at best, uses the ECM to control the grounding on the relay for the clutch. as in, it MAY be able to say "hey idiot turn on" when its foggy kinda thing and then also WOT cut out. at best
My 1990 car had WOT cut out relay, so it would be a relay or 2 that control out side of the controls. the ac controls having direct wire to the ac clutch somehow, then the ECM being able to provide an additional or override the grounding.

but im unsure what an 87 tbi computer can do since 1990 TunedPortFuelInjection is different

The compressor was also an HR6 but I am unsure what an 87 TBI would use, probably r4 or another type compressor

 

[AuroraGirl]

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@eric 87

 

[eric 87]

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@eric 87

I appreciate. Is that for an 87....I note the different compressor. Mine is the little round I think A4 or is it R4. Anyway I didn't know if the wiring went through the computer at all or if it were separate and not part of that harness. Someone said to ground a wire on a relay or something but then it would stay engaged at WOT and if I understand I would have to add a throttle solenoid?
I really wanted this to stay a simple project but now I am swapping fuel system as well. I was going to just use the regulator to cut the pressure back for the carb. But Summit sent me (my mistake or theirs?) the wrong regulator without the bypass. Same number I had written down on my grocery list but my list said 12-803BP and they sent a 12-803....no bypass. So now I am switching out 6 way selector for a 3 way. An electric fuel pump wired through both a relay AND the oil pressure switch. I will cut that pigtail to wire it in properly as well as the relay. I will do this right if it kills me in the process. But I will post all info and all part numbers for reference. I bet it has been done but I be darn if I could find it! Thanks for the picture to at least give me some guidance on the harness.

 

[AuroraGirl]

I appreciate. Is that for an 87....I note the different compressor. Mine is the little round I think A4 or is it R4. Anyway I didn't know if the wiring went through the computer at all or if it were separate and not part of that harness. Someone said to ground a wire on a relay or something but then it would stay engaged at WOT and if I understand I would have to add a throttle solenoid?
I really wanted this to stay a simple project but now I am swapping fuel system as well. I was going to just use the regulator to cut the pressure back for the carb. But Summit sent me (my mistake or theirs?) the wrong regulator without the bypass. Same number I had written down on my grocery list but my list said 12-803BP and they sent a 12-803....no bypass. So now I am switching out 6 way selector for a 3 way. An electric fuel pump wired through both a relay AND the oil pressure switch. I will cut that pigtail to wire it in properly as well as the relay. I will do this right if it kills me in the process. But I will post all info and all part numbers for reference. I bet it has been done but I be darn if I could find it! Thanks for the picture to at least give me some guidance on the harness.

Are you using a quadrajet? I have 2 oldsmobile 260s with dualjets(half a qjet, uses a lot of the same parts) with pull offs and kickup solenoids, i can show you closer look to get an idea. Also, the R4 pictured is the "pancake" compressor that is considered meh overall but it was stock for many years in squares. the diagram I sent was also for a 87 yes.

On your truck, you dont need to worry abotu a WOT cutout unless you want a luxury convenience most people will just turn off the AC if they need the power truly

Its prob not hard to wire but it would be custom for your situation to try and replicate. I would follow an early 80s(if they used R4) wiring diagram and maybe swap the HVAC harness and stuff to get the AC wiring for your compressor, it would be easiest in my view.