A/C Compressor coil chronicles

2917 Views 19 Replies 7 Participants Last post by hpark21, 15 d ago

bobby's oddity

Discussion Starter · Jun 28, 2020

Good day Ody Club:

Wondering if anyone out there has experience with failures of the coil on the A/C compressor. I have an '08 LX and have been trying to figure out A/C failures.

Symptoms:
-Sudden A/C failure in warm weather (30 Celsius).
-Melting and subsequent failure of compressor coil/solenoid.

Actions so far:
-Electrical troubleshooting: everything up to the compressor appears to be working. Confirmed with multimeter that relay switch is sending power to the coil. Ground wire is also good.
-Took off pulley wheel. Clutch in fair condition, bearing slightly 'sandy' but still turning OK.
-Coil/Solenoid had evidence of melting and was showing open circuit.
-Replaced with new coil. Also replaced bearing, pulley, and clutch (whole assembly). Clutch to pulley gap was 0.015" per installation manual recommendation.
-A/C worked great after turning on for a few minutes so put the car back together
-A/C failed again a few days later on a warm day after being on for ~20 minutes
-Took clutch assembly apart again and the new coil was failed almost identically to the first coil

Anyone experienced anything similar?

Thinking possible causes:
-Mechanical friction (seems unlikely since snap rings holding everything in place and parts seem to rotate freely by hand)
-Clutch not properly engaged (also seems unlikely since I replaced the clutch, measured the gap with a depth gauge, and there was no sign that the clutch had heated up)
-Clutch not moving and causing persistent initial coil current (also seems unlikely since clutch only moves a very small distance anyway)
-Current too high due to faulty wiring upstream of compressor. But how could this be if the A/C is turning on and apparently working fine after I install a new solenoid??

Any thoughts or experience related to this would be greatly appreciated.

See less See more

1 - 20 of 20 Posts

marvinstockman

· #2 · Jun 29, 2020

Bad bearings in the compressor? Did you turn compressor by hand with clutch engaged..

A hot compressor may be burning up the coil. Remember, the coil has both a fuse and a relay, and excessive coil current should blow fuse and burn up relay.

Get a cheap infrared thermometer and measure clutch and compressor temperature while running. Compare temperature to another vehicle.

John Clark

· #3 · Jun 29, 2020

How about some photos?

Excessive current would blow the fuse. Doubtful it would burn up the relay. A burned and worn relay could, however, drop enough voltage to cause low voltage at the clutch, possibly causing the clutch to not pull in enough and heating up the clutch assembly.

Also, what brand of clutch/coil assembly did you install?

bobby's oddity

Discussion Starter · #4 · Jul 1, 2020

John Clark said:
How about some photos?

Excessive current would blow the fuse. Doubtful it would burn up the relay. A burned and worn relay could, however, drop enough voltage to cause low voltage at the clutch, possibly causing the clutch to not pull in enough and heating up the clutch assembly.

Also, what brand of clutch/coil assembly did you install?

Thanks for the Reply John. Here is a photo of the burnt solenoids. Original one on the top. The replacement assembly came off a 2017 Odyssey I found at the junkyard, so likely OEM (unfortunately can't read the writing on the solenoid anymore).

I think my next step is going to be to build my spare compressor with a new solenoid (running out of compatible Hondas at the junkyard) and hook it up to a 12V power supply. I can then wire in the relay switch from my van and see if there is a large voltage drop across it.

Any other thoughts?

See less See more

John Clark

· #5 · Jul 3, 2020

Just a thought here, your compressor clutch isn't powered on all the time, is it? A common failure on these is that the relay sticks closed and the clutch is powered on 24/7.

bobby's oddity

Discussion Starter · #6 · Jul 3, 2020

John Clark said:
Just a thought here, your compressor clutch isn't powered on all the time, is it? A common failure on these is that the relay sticks closed and the clutch is powered on 24/7.

No it was definitely cycling. You could very clearly feel the A/C get cold when the button was pushed. I also popped out the A/C clutch relay switch and used it on a spare solenoid and external power supply. With 14V and 3A applied, the relay was only dropping 20-30mV so it appears to be working as designed.

bobby's oddity

Discussion Starter · #7 · Jul 3, 2020

marvinstockman said:
Bad bearings in the compressor? Did you turn compressor by hand with clutch engaged..

A hot compressor may be burning up the coil. Remember, the coil has both a fuse and a relay, and excessive coil current should blow fuse and burn up relay.

Get a cheap infrared thermometer and measure clutch and compressor temperature while running. Compare temperature to another vehicle.

Possible, I will have to try that with the next iteration. Seems unlikely since the melting was localized to the side opposite the compressor. It also felt pretty smooth when I spun the clutch by hand.

Will report back the next time. Running out of compatible Hondas to rip solenoids from at the wreckers.

bobby's oddity

Discussion Starter · #8 · Jul 13, 2020

Well I think I found the problem (knocking on wood here). After acquiring another coil, I spliced in a connection to the power supply line just before the solenoid plug. On an oscilloscope, I was reading 0V relative to engine block with no A/C engaged (as expected). When the A/C was turned on, The reading jumped to 6.8-6.9V, but it should be closer to alternator voltage. I confirmed that there was still full voltage at the relay switch input (~14.2V) so good power to the fuse box). Interestingly, I also got 6.5V at the compressor with the solenoid leads unplugged (no load).

It was also possible to watch the clutch spinning and slipping periodically which I assume is because it only has 50% of nominal voltage/current/force. This would have made a lot of heat and I assume, eventually cooked both coils. The clutch gap was ~0.02" larger than when I installed it so clearly had worn down some.

This narrows the problem down to the relatively short wiring harness between the relay switch and the A/C clutch coil. Just for fun I popped in a relay that I'd pulled from the junkyard, and suddenly I was getting a no-load reading of 14.2V at the splice. Another trial with the solenoid connected gave a reading of 13.9V at the splice while loaded, which seems reasonable. A bit of a mystery since I'd tested that relay in an external DC power supply and it only dropped 20mV under a 13V, 3A load.

Generally I'm a proponent of root-cause analysis vs. parts cannon, but seems like relays are a common problem with Odyssey A/C systems. If anyone is having a problem with A/C not working properly, the relay is not a bad thing to swap out since it's cheap and takes 30 seconds. Hope someone finds this thread useful in the future, I don't want to admit how long it took me to find out that it was a stinking relay.

See less See more

John Clark

· #9 · Jul 13, 2020

bobby's oddity said:
Well I think I found the problem (knocking on wood here). After acquiring another coil, I spliced in a connection to the power supply line just before the solenoid plug. On an oscilloscope, I was reading 0V relative to engine block with no A/C engaged (as expected). When the A/C was turned on, The reading jumped to 6.8-6.9V, but it should be closer to alternator voltage. I confirmed that there was still full voltage at the relay switch input (~14.2V) so good power to the fuse box). Interestingly, I also got 6.5V at the compressor with the solenoid leads unplugged (no load).

It was also possible to watch the clutch spinning and slipping periodically which I assume is because it only has 50% of nominal voltage/current/force. This would have made a lot of heat and I assume, eventually cooked both coils. The clutch gap was ~0.02" larger than when I installed it so clearly had worn down some.

This narrows the problem down to the relatively short wiring harness between the relay switch and the A/C clutch coil. Just for fun I popped in a relay that I'd pulled from the junkyard, and suddenly I was getting a no-load reading of 14.2V at the splice. Another trial with the solenoid connected gave a reading of 13.9V at the splice while loaded, which seems reasonable. A bit of a mystery since I'd tested that relay in an external DC power supply and it only dropped 20mV under a 13V, 3A load.

Generally I'm a proponent of root-cause analysis vs. parts cannon, but seems like relays are a common problem with Odyssey A/C systems. If anyone is having a problem with A/C not working properly, the relay is not a bad thing to swap out since it's cheap and takes 30 seconds. Hope someone finds this thread useful in the future, I don't want to admit how long it took me to find out that it was a stinking relay.

Isn't that what I suggested back in my first reply, post #3?

John Clark said:
How about some photos?

Excessive current would blow the fuse. Doubtful it would burn up the relay. A burned and worn relay could, however, drop enough voltage to cause low voltage at the clutch, possibly causing the clutch to not pull in enough and heating up the clutch assembly.

Also, what brand of clutch/coil assembly did you install?

bobby's oddity

Discussion Starter · #10 · Jul 13, 2020

John Clark said:
Isn't that what I suggested back in my first reply, post #3?

Yes it is. I'm reporting the results so others may learn. Also is interesting to point out that the relay passed a simulated load using an external DC power supply, yet still does not function properly in the vehicle.

John Clark

· #11 · Jul 13, 2020

There is an improved relay to use in these. See the attachment.

John Clark

· #12 · Jul 13, 2020

Also, while you put a 3A load on it, which is about right considering the clutch coils are about 4 ohms, remember that this circuit has a collapsing magnetic field when the coil is turned off. This causes a voltage spike in the system that will go through that relay. This is how your ignition coils work. So, it's hard to simulate the actual circuit for a magnetic clutch like this. Many clutch circuits have a diode in them to protect the circuit but I don't see one in the wiring diagrams for these vans.

Daretodream

· #13 · Jul 14, 2020

bobby's oddity said:
Yes it is. I'm reporting the results so others may learn. Also is interesting to point out that the relay passed a simulated load using an external DC power supply, yet still does not function properly in the vehicle.

It seems you have removed the AC coil a number of times. Any tips to help remove the circlip on the coil because I can't seem to get mine off?

bobby's oddity

Discussion Starter · #14 · Jul 24, 2020 (Edited)

Daretodream said:
It seems you have removed the AC coil a number of times. Any tips to help remove the circlip on the coil because I can't seem to get mine off?

Sorry just noticed this. I didn't have much trouble with this, only advice I have is get a good quality snap-ring removal tool (buy once, cry once). It's kind of hard to get at, I could only get the tool in by unclipping the plug at the back of the compressor, then undid the 4x12mm bolts that mount it on the engine block bracket. Careful though because now it's hanging from pressurized hoses. I could kind of rotate it towards the wheel. With someone holding the compressor in position it wasn't too bad to get the snap ring tool in there and pop it out. Good luck

bobby's oddity

Discussion Starter · #15 · Jul 24, 2020

John Clark said:
Also, while you put a 3A load on it, which is about right considering the clutch coils are about 4 ohms, remember that this circuit has a collapsing magnetic field when the coil is turned off. This causes a voltage spike in the system that will go through that relay. This is how your ignition coils work. So, it's hard to simulate the actual circuit for a magnetic clutch like this. Many clutch circuits have a diode in them to protect the circuit but I don't see one in the wiring diagrams for these vans.

Yeah I was kind of surprised that I didn't see a diode for the back EMF spike on the wiring diagram. There is one for the relay switch but I also didn't see one for the coil, which is a much larger inductance I would assume. Maybe that's why the relay issue is common.

With the 3A benchtop load, it was actually using a real A/C compressor and coil with a switch feeding the control leads on the relay switch, so should be very similar to real life. Repeated this test again with the same result as before. The leads are in good shape too so it's still a mystery.

Thanks for that bulletin.

bobby's oddity

Discussion Starter · #16 · Jul 24, 2020

Also, for future reference here is a solenoid with a slot milled into it in case you wondered. I'm not sure exactly where the open--circuit was on this one but a common occurrence for over-heated coils. Likely the bubbled/chowdered material on the face was melted/solidified bobbin material.

See less See more

2

John Clark

· #17 · Jul 25, 2020

Cool pic...The wires are thick enough inside that I doubt they fail internally. I'll bet it's where the wires go in and out somewhere.

keenan.m.holland

· #18 · 16 d ago

bobby's oddity said:
Sorry just noticed this. I didn't have much trouble with this, only advice I have is get a good quality snap-ring removal tool (buy once, cry once). It's kind of hard to get at, I could only get the tool in by unclipping the plug at the back of the compressor, then undid the 4x12mm bolts that mount it on the engine block bracket. Careful though because now it's hanging from pressurized hoses. I could kind of rotate it towards the wheel. With someone holding the compressor in position it wasn't too bad to get the snap ring tool in there and pop it out. Good luck

I've got a dreaded 2010 EX-L. I've been able to get the outer ring clip out with a flat screwdriver and a 90deg pick... The inner ring clip is the hard one.... I used just a regular ring clip pliers but took several attempts because it's a VERY tight area to work in. Get the pins in the clip holes is the trick with the frame right there .. but it's doable.... Just be patient and be prepared to try a dozen times. I wouldn't risk un bolting the compressor unless you get desperate. One wrong move and an hours struggle can turn into a weekend battle.

christos

· #19 · 15 d ago

Daretodream said:
It seems you have removed the AC coil a number of times. Any tips to help remove the circlip on the coil because I can't seem to get mine off?

The secret is to use a good set of snap ring pliers. I bought a pair of Miller 9764 pliers, and they worked great. Unfortunately, they seem to be priced outrageously new, (I bought used), but you can try to get something similar. Two important features: (a) they are strong, and (b) they are deep, which is what you need. I tried and failed miserably using regular snap ring pliers. If I need to do the clutch again I know I have the right tool.

hpark21

· #20 · 15 d ago

keenan.m.holland said:
I've got a dreaded 2010 EX-L. I've been able to get the outer ring clip out with a flat screwdriver and a 90deg pick... The inner ring clip is the hard one.... I used just a regular ring clip pliers but took several attempts because it's a VERY tight area to work in. Get the pins in the clip holes is the trick with the frame right there .. but it's doable.... Just be patient and be prepared to try a dozen times. I wouldn't risk un bolting the compressor unless you get desperate. One wrong move and an hours struggle can turn into a weekend battle.

My suggestion is opposite, DO try to unbolt the compressor if you can so that you can attack the snap ring from more favorable angle. I TRIED to take the compressor out but part way through one of the bolt got stuck while coming out. My mechanic told me that MOST LIKELY the bolt will snap if I try harder so I put the bolts back in but if you can unbolt it then it probably is way to go.

Do search for "master cylinder snap ring pliers".

1 - 20 of 20 Posts