Back in June, I posted about some work I was doing to my A/C on my '97 Civic LX. Everything is working fine (most of the time), but I have one very annoying, intermittent problem that I would like to solve.

Whenever I'm driving my car with the A/C on, it will occasionally let go with the a/c clutch and make a terrible noise. Sometimes it will run with absolutely no problems, and when it does slip, I can cycle the A/C off and then right back on to stop the slipping. At first, I suspected a system pressure problem that made the compressor harder to turn under certain conditions, but now I'm thinking maybe an electrical problem.

The problem is completely random, it can happen under high (>3,500) or low rpm. It does seem to be slightly worse when the car has been sitting in a hot parking lot at work all day (but this is also stop and go driving instead of highway).

Could a weak magnetic coupling be the problem? It seems though if the magnet let go, then it would simply disengage. I am completely lost why it sometimes works and sometimes does not. Any ideas?

 

Can you describe the noise?

Have you checked the gap between the compressor pulley and armature plate?

 

Very loud metallic squeal. I confirmed visually that it is the a/c clutch slipping against the pulley.

I did put a different clutch on the a/c when I had it apart because the old one appeared worn and it was also squealling.

I checked the gap when I had the compressor out in June. It measured between 0.55 and 0.6 (within tolerance), so I assumed that wasn't the issue.

 

Is the belt slipping? If not, you may need to replace the pulley and clutch again.

 

This is a longshot, but for the sake of discussion...

My wife's car has a Mitsubishi motor. Her A/C did the same thing (as you describe) off n' on.

After burning up a couple of belts (from lock-ups), I took the clutch off and inspected it. Everything looked fine, so I reinstalled it.

After a year of this non-sense, I finally figured out that the shaft on the compressor was worn, and the pulley was (sometimes) rubbing against the compressor body. If the engine compartment got hot enough, the metal would expand, the clutch would rub against the compressor body, and it would lock-up solid. When it cooled down, everything was fine again.

For a quick fix, I cut some thin brass shim stock and placed it inside the hole on the clutch. That got the clutch assembly away from the compressor, by a few 1000ths. LoL! That fixed it for another year.

Finally, three years later, I had enough of this, and put a whole new compressor/clutch assembly in.

Damn, those Jap A/C compressors are expensive -- like $600, if I remember.

I hated throwing out a perfectly good compressor, just because the shaft was worn -- but watcha gonna do?!?!? The OEM tolerances were too tight, and putting a new clutch on it wouldn't do jack.

Anyway, perhaps you have a similar problem, e.g. worn shaft...

 

I'll take another look, but I'm pretty sure the noise is caused by the a/c clutch plate rubbing against the pulley. Although, both seemed to spin freely when I had the belt off.

 

Ok, I've observed the clutch slipping against the pulley and causing the noise.

I'm still at a complete loss to understand why the clutch will engage and turn, and then at an indeterminate time release and slip against the drive pulley. I've noted a few more observations:

1. The problem seems at its worst when the system is first turned on. May be a coincidence, but temperatures here have been extremely hot (~100 degrees) this past week. After sitting in the parking lot at work all day, I have to cycle the A/C on and off 4 or 5 times and the problem gradually diminishes. This is also during city driving with frequent stops and accelerations.

2. The problem seems to go away after the system begins to cool the cabin and with highway driving.

3. Whenever the slipping occurs, I can always fix it by cycling the A/C off and right back on. I can also fix it by decelerating and "re-accelerating".

Is it normal for system pressure to fluctuate during operation? Could this be the cause of the slipping?

What would be the consequence of too much gap between the a/c clutch and pulley?

Any other thoughts?

 

Check the pressure(s)...

 

I would agree with checking the pressures. Not that's it's a Honda, but my truck was doing a similar thing. It would sit all day at work, then when I started it up it would make a horrible grinding noise for a few seconds then go away, then as I would drive away it would do this again a few times. And like yours, it would quit doing it after I have been moving for a couple minutes, and every once and a while it would do it again while driving. If I had the hood popped when I first turned it on and was looking a the compressor it would vibrate a lot while it was making the noise. I thought it was pressure also so I hooked up one of those gauges you get from the auto parts store for the DIY A/C refill kits and it was reading 95-100psi (red zone). So I totally discharged my cooling system and refilled it to the amount of refrigerant specified in the book, and since then it quit making the noise and actually cools a lot better also. Just FYI

The system pressure will fluctuate based on ambient temperature. The hotter it is the higher the pressure in the system.