AC Compressor Clutch Problems

[BobbyZ]

I have been slowly fixing a few things on my newly aquired 280zx turbo whenever I get the time. This weekend I addressed the A/C. The previous owner had removed the belt to the A/C compressor at some point in this cars past and I wanted to see if it still worked. I put a new belt on there and the A/C seems to work great!

 

However, when the A/C is turned off the clutch on the compressor makes a very loud rattle. It looks like the clutch is having a hard time freewheeling, you can see the compresser pully jerking around as the clutch catches and then lets go. The compressor may have sat for years without turning so I am assuming that the bearings are frozen on the clutch. When the A/C is engaged it is totally quiet so I am pretty sure that the compressor itself is fine.

 

Can I spray the compressor clutch with lubricant to free it up or am I going to damage the clutch that way?

 

Am I going to have to replace the clutch on the compressor?

[zcarnut]

As long as the pulley is rotating, the bearings are turning as well regardless of whether the clutch is engaged or not, so they cannot be seized. That is, the bearings just support the AC compressor pulley. The clutch disc on the front of the compressor is connected internally to the swashplate which houses the rotary pistons. When the clutch is engaged, the clutch disc is flexed by a magnetic field and makes contact with the pulley.

 

Rust can build up on the contact surfaces of the pulley and clutch disc, especially when the compressor is inactive, but the rust layer is removed after a few cycles of on-off operation. There is spec for the air gap between the two contact surfaces (.020†to .015†or so) when the clutch is disengaged.

 

Be careful with the lubricate as friction is necessary for the clutch to operate.

 

You can remove the clutch disc for a closer inspection by first removing the lock washer and then the 8mm nut at the front of the compressor. Use a snap-ring pliers or a needle-nose pliers to remove the threaded collar and gently pry the disc off. Be sure to watch out for the air gap adjusting shims and the shaft key! You do not want to loose them.

 

Also, make sure that the head pressure at the output of the compressor is not too high. Measure this with a refrigerant gauge screwed into the high side Schrader valve. It should be less than 200psi. Too high a level will cause the ac compressor to actually rotate backwards when it has been disengaged. Too much pressure is caused by a restriction in the condenser or receiver/dryer or having too much R12 in the system.

[BobbyZ]

I drove the car to lunch and I am realizing that the compressor itself is making a lot of noise when the A/C is on. Once I turn the A/C off all I get is the noise from the A/C clutch. I may just pull the belt off again and get used to having the windows open.

 

I think the only thing I could do is replace the compressor, not really an option due to the cost. (compressor + recharge = $$$)