strange A/C clutch issue
Thread Starter
Instructor
Joined: Mar 2014
Posts: 118
Likes: 5
From: Houston TX
strange A/C clutch issue
At least, strange to me. I've never had this issue before.
Basically, my A/C clutch is slipping. I installed a new clutch when the bearing starting making noise a month ago.
The A/C worked fine for a few weeks, then I started noticing what felt like a "sputter" in how the car was running, but it turned out the A/C clutch is starting to erratically slip while the A/C is engaged.
The gap has been and is still set properly, so I'm wondering if the compressor may be starting to lock up, because if it is....I'll leave it shut off until I can replace it.
Has anyone ever dealt with this issue?
Basically, my A/C clutch is slipping. I installed a new clutch when the bearing starting making noise a month ago.
The A/C worked fine for a few weeks, then I started noticing what felt like a "sputter" in how the car was running, but it turned out the A/C clutch is starting to erratically slip while the A/C is engaged.
The gap has been and is still set properly, so I'm wondering if the compressor may be starting to lock up, because if it is....I'll leave it shut off until I can replace it.
Has anyone ever dealt with this issue?
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
is there oil splatter under the hood??
Even IF the comp were trying to seize, the clutch should not slip....most times the belt slips on the seized pulley.
A comp that's tired makes noise usually....rattles as the pistons inside beat around in the rotary barrel.(depends on compressor type) but they all rattle near the end. If it has never been opened up, or the gas changed, and oil lost, its probably ok.
I'd look for oil on the clutch and close the gap a hair. A business card thickness is the approx gap.
Even IF the comp were trying to seize, the clutch should not slip....most times the belt slips on the seized pulley.
A comp that's tired makes noise usually....rattles as the pistons inside beat around in the rotary barrel.(depends on compressor type) but they all rattle near the end. If it has never been opened up, or the gas changed, and oil lost, its probably ok.
I'd look for oil on the clutch and close the gap a hair. A business card thickness is the approx gap.
Thread Starter
Instructor
Joined: Mar 2014
Posts: 118
Likes: 5
From: Houston TX
The clutch and compressor are dry and no oil anywhere. not on hood or any corresponding components.
Clutch gap is set to .022 with my feeler gauge.
I just replaced the coil under the clutch pulley today thinking it might be bad and not pulling enough of a magnetic field to hold the clutch against the pulley. No dice...still same issue.
Clutch gap is set to .022 with my feeler gauge.
I just replaced the coil under the clutch pulley today thinking it might be bad and not pulling enough of a magnetic field to hold the clutch against the pulley. No dice...still same issue.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Hard to say without looking at it. The bad bearing may have created uneven wear on the Face Plate and Pulley. You could check the air gap at several places. Also, try .020 though being a tad off shouldn't create anything other than a little noise when it engages. Do make sure that you can turn the shaft by hand with the belt off.
I'd have it leaked checked with an electronic leak detector - you're not going to see an Evaporator Leak. At least check operating pressures and with it running, disconnect the Blower Motor. That should drop the Low below the Cutoff threshold and you can see what it does when it cycles off.
Assuming it's an R4 compressor, a new one is (relatively) cheap enough. If it's 30 years old, consider replacing it - stay away from the Discounters. Throwing a new Clutch Assembly at it may not fix it.
I'd have it leaked checked with an electronic leak detector - you're not going to see an Evaporator Leak. At least check operating pressures and with it running, disconnect the Blower Motor. That should drop the Low below the Cutoff threshold and you can see what it does when it cycles off.
Assuming it's an R4 compressor, a new one is (relatively) cheap enough. If it's 30 years old, consider replacing it - stay away from the Discounters. Throwing a new Clutch Assembly at it may not fix it.
Thread Starter
Instructor
Joined: Mar 2014
Posts: 118
Likes: 5
From: Houston TX
Good idea, I'll check the voltage tonight.
It happens any time the A/C or Defrost is engaged, with both engine hot or cold and ambient temp hot or cooler.
The new clutch worked fine for about 2 weeks before doing this.
I have not purchased a FSM for it yet. Does anyone know which of the two wires going to the pump are voltage and which is ground?
I also see that there is a resistor jumping between them. Is that something that could get fried and cause this?
It happens any time the A/C or Defrost is engaged, with both engine hot or cold and ambient temp hot or cooler.
The new clutch worked fine for about 2 weeks before doing this.
I have not purchased a FSM for it yet. Does anyone know which of the two wires going to the pump are voltage and which is ground?
I also see that there is a resistor jumping between them. Is that something that could get fried and cause this?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
It's not a resistor but a Diode. It's used to make sure that electricity only flows to ground . When the clutch cycles off, the magnetic field collapses and without it, electricity could flow back through the coil and damage it as well as the circuitry that controls engagement; ie, the Dash Controls which would not be protected by the fuse. If the coil was damaged, doubt it would engage at all, though if you're curious, a DVM should only show continuity towards ground.
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Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
It's not a resistor but a Diode. It's used to make sure that electricity only flows to ground . When the clutch cycles off, the magnetic field collapses and without it, electricity could flow back through the coil and damage it as well as the circuitry that controls engagement;
This is an interesting experiment: Use any 12v relay you've got in your junk box. Hook the coil terminals to a 12v battery, but leave one wire loose. Don't use a switch. Touch the wire to the coil terminal, and as you remove the wire frome the terminal, you should see a small spark. Put a diode across the coil terminals, cathode to +12. Repeat this action on the relay terminal, and notice . . . no spark!
This collapse of the magnetic field and arcing is good in an ignition coil and spark plug, but not in your A/C!
Last edited by Hot Rod Roy; May 7, 2014 at 02:14 PM.
Thread Starter
Instructor
Joined: Mar 2014
Posts: 118
Likes: 5
From: Houston TX
Thanks for all the replies guys, but last it's apparent to me now that the pump is crapped out.
I turned it on to check voltage....the clutch engaged and I was getting exactly 12.2V when I realized it wasn't slipping.
I checked for cold air.......nothing......then it locked up and the clutch disk started screaming and throwing sparks until I quickly unplugged the low pressure switch.
So I wasted my money buying a new clutch when I did.
Oh well, I'll get a pump and drier.
One more question, if anyone might know or take a stab at a guess...
The A/C was converted to R134 long before I got it, but the conversion sticker is faded too bad to read what oil they used.
What would have been the recommended A/C oil used in a conversion?
I just don't want to mix oils.
I turned it on to check voltage....the clutch engaged and I was getting exactly 12.2V when I realized it wasn't slipping.
I checked for cold air.......nothing......then it locked up and the clutch disk started screaming and throwing sparks until I quickly unplugged the low pressure switch.
So I wasted my money buying a new clutch when I did.
Oh well, I'll get a pump and drier.
One more question, if anyone might know or take a stab at a guess...
The A/C was converted to R134 long before I got it, but the conversion sticker is faded too bad to read what oil they used.
What would have been the recommended A/C oil used in a conversion?
I just don't want to mix oils.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
SunCr, your descrition of the diode function is close. The engagement and disengagement of the compressor clutch is done by the low side switch, as you know (not the dash controls). When the low side switch opens, voltage is removed from the clutch coil, and the magnetic field in the coil collapses. The inductance of the coil causes the current to continue flowing, and without the diode, this will cause a spark in the contacts of the low side switch as it is opening. The diode will provide a path for this current spike to ground, which protects the low side switch from being damaged by the arc.
This is an interesting experiment: Use any 12v relay you've got in your junk box. Hook the coil terminals to a 12v battery, but leave one wire loose. Don't use a switch. Touch the wire to the coil terminal, and as you remove the wire frome the terminal, you should see a small spark. Put a diode across the coil terminals, cathode to +12. Repeat this action on the relay terminal, and notice . . . no spark!
This collapse of the magnetic field and arcing is good in an ignition coil and spark plug, but not in your A/C!
This is an interesting experiment: Use any 12v relay you've got in your junk box. Hook the coil terminals to a 12v battery, but leave one wire loose. Don't use a switch. Touch the wire to the coil terminal, and as you remove the wire frome the terminal, you should see a small spark. Put a diode across the coil terminals, cathode to +12. Repeat this action on the relay terminal, and notice . . . no spark!
This collapse of the magnetic field and arcing is good in an ignition coil and spark plug, but not in your A/C!
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
SunCr, your descrition of the diode function is close. The engagement and disengagement of the compressor clutch is done by the low side switch, as you know (not the dash controls). When the low side switch opens, voltage is removed from the clutch coil, and the magnetic field in the coil collapses. The inductance of the coil causes the current to continue flowing, and without the diode, this will cause a spark in the contacts of the low side switch as it is opening. The diode will provide a path for this current spike to ground, which protects the low side switch from being damaged by the arc.
This is an interesting experiment: Use any 12v relay you've got in your junk box. Hook the coil terminals to a 12v battery, but leave one wire loose. Don't use a switch. Touch the wire to the coil terminal, and as you remove the wire frome the terminal, you should see a small spark. Put a diode across the coil terminals, cathode to +12. Repeat this action on the relay terminal, and notice . . . no spark!
This collapse of the magnetic field and arcing is good in an ignition coil and spark plug, but not in your A/C!
This is an interesting experiment: Use any 12v relay you've got in your junk box. Hook the coil terminals to a 12v battery, but leave one wire loose. Don't use a switch. Touch the wire to the coil terminal, and as you remove the wire frome the terminal, you should see a small spark. Put a diode across the coil terminals, cathode to +12. Repeat this action on the relay terminal, and notice . . . no spark!
This collapse of the magnetic field and arcing is good in an ignition coil and spark plug, but not in your A/C!
on a manual system.
the opt-68 electrical a/c control is a different animal.
That diode is there to protect the $125 BCM or a/c power module as its called.
The curious thing is, that the only way something could happen is IF this module failed and allowed current to flow backward thru the system, so the diode is protecting the thing that could cause the problem, only after it failed. So, the diode is an "after-thought" of sorts....meaningless.
I chopped mine out 14 years ago and have not looked back......
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Michael,
IIWM,
I'd buy the flush kit as well and do this RIGHT.
The secret to doing good a/c work is CLEANLINESS !
flush the insides, blow out each section with solvent or flush, blow it dry, (spend extra time on the evap 'cause that's like blowing thru a 20' pipe there is so much diffusion) and then reconnect each section adding a couple oz at each major connection, evap, dryer, condenser, etc....seal it all up then evacuate. Auto parts store loan out pumps and gauges with a deposit.
Remember, the compressor sent debris thru the ENTIRE system...not just the dryer. The orifice will have a bunch of crap and the evap will have a collection of debris in the bottom...that's why you blow it ALL out in sections.
Buy a new orifice...blue tube or a smart tube. Cheap insurance. Dryers are stupid cheap...$10
IIWM,
I'd buy the flush kit as well and do this RIGHT.
The secret to doing good a/c work is CLEANLINESS !
flush the insides, blow out each section with solvent or flush, blow it dry, (spend extra time on the evap 'cause that's like blowing thru a 20' pipe there is so much diffusion) and then reconnect each section adding a couple oz at each major connection, evap, dryer, condenser, etc....seal it all up then evacuate. Auto parts store loan out pumps and gauges with a deposit.
Remember, the compressor sent debris thru the ENTIRE system...not just the dryer. The orifice will have a bunch of crap and the evap will have a collection of debris in the bottom...that's why you blow it ALL out in sections.
Buy a new orifice...blue tube or a smart tube. Cheap insurance. Dryers are stupid cheap...$10
Pro
Joined: Aug 2007
Posts: 668
Likes: 38
From: Austin TX
I went through two Auto#one clutches in 6 months before i realized the design couldn't handle the Corvette's high RPM capability. I replaced it with a more factory design clutch from Corvette Whatever and been running it for 4 years now.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I doubt aftermarket a/c part failures have anything to do with hp; high rpm, etc - the pros on the forum at www.ackits.com rip them for all the right reasons daily.
Racer
Joined: Sep 2007
Posts: 493
Likes: 0
From: Eden Utah
Michael,
IIWM,
I'd buy the flush kit as well and do this RIGHT.
The secret to doing good a/c work is CLEANLINESS !
flush the insides, blow out each section with solvent or flush, blow it dry, (spend extra time on the evap 'cause that's like blowing thru a 20' pipe there is so much diffusion) and then reconnect each section adding a couple oz at each major connection, evap, dryer, condenser, etc....seal it all up then evacuate. Auto parts store loan out pumps and gauges with a deposit.
Remember, the compressor sent debris thru the ENTIRE system...not just the dryer. The orifice will have a bunch of crap and the evap will have a collection of debris in the bottom...that's why you blow it ALL out in sections.
Buy a new orifice...blue tube or a smart tube. Cheap insurance. Dryers are stupid cheap...$10
IIWM,
I'd buy the flush kit as well and do this RIGHT.
The secret to doing good a/c work is CLEANLINESS !
flush the insides, blow out each section with solvent or flush, blow it dry, (spend extra time on the evap 'cause that's like blowing thru a 20' pipe there is so much diffusion) and then reconnect each section adding a couple oz at each major connection, evap, dryer, condenser, etc....seal it all up then evacuate. Auto parts store loan out pumps and gauges with a deposit.
Remember, the compressor sent debris thru the ENTIRE system...not just the dryer. The orifice will have a bunch of crap and the evap will have a collection of debris in the bottom...that's why you blow it ALL out in sections.
Buy a new orifice...blue tube or a smart tube. Cheap insurance. Dryers are stupid cheap...$10
Do exactly as he says and you will be ok. If not then you will be doing it again. Wait until you see how much the cleaning fluid costs. Whooeee
Thread Starter
Instructor
Joined: Mar 2014
Posts: 118
Likes: 5
From: Houston TX
I will be doing this soon.
I have a vac pump and gauges. I'll get some more flush and borrow my friends flush tank.
I have a couple more pressing issues to tackle first, then I'll get this A/C working again.
I'm just upset that I didn't just buy a new compressor when I bought the clutch. $85 for a new clutch, $145 for a reman pump with clutch.
Oh well.....live and learn.
Thanks again all.
I have a vac pump and gauges. I'll get some more flush and borrow my friends flush tank.
I have a couple more pressing issues to tackle first, then I'll get this A/C working again.
I'm just upset that I didn't just buy a new compressor when I bought the clutch. $85 for a new clutch, $145 for a reman pump with clutch.
Oh well.....live and learn.
Thanks again all.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
That diode is there to protect the $125 BCM or a/c power module as its called.
The curious thing is, that the only way something could happen is IF this module failed and allowed current to flow backward thru the system, so the diode is protecting the thing that could cause the problem, only after it failed. So, the diode is an "after-thought" of sorts....meaningless.
The curious thing is, that the only way something could happen is IF this module failed and allowed current to flow backward thru the system, so the diode is protecting the thing that could cause the problem, only after it failed. So, the diode is an "after-thought" of sorts....meaningless.
If you don't think back EMF is a big deal, it's what fires your spark plugs...
Pro
Joined: Aug 2007
Posts: 668
Likes: 38
From: Austin TX
I doubt aftermarket a/c part failures have anything to do with hp; high rpm, etc - the pros on the forum at www.ackits.com rip them for all the right reasons daily.