A/C clutch sticks...

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This is going on the third year I've had this issus. My air conditioner works great in my 1997 Nissan pickup (2.4 liter) but after running for a short period (20 mins usually), the A/C clutch stops engaging. I can tap the clutch itself with a pair of pliers or other blunt object and it will kick in and work as normal until the next time it cycles. Then it stops again.

Do you guys think I just need to replace the clutch or is there any chance there's another component to look to? I know absolutely NOTHING about A/C units other than the basic principles of operation.

Thanks!!
 
Excessive clutch gap. As the engine warms up, clutch coil warms up, resistance increases, magnetic force lessens.

Check your clutch clearance (at 3 places), reshim it closer to the pulley face if needed. I always shimmed my clutches close/low side of spec. As long as it doesn't drag wwhen the AC is off, you are good to go.
 
Thanks very much for the quick reply. Please go into detail as to what gap I measure and what I use to shim it with.

does this involve removing the clutch from the compressor?

I have zero experience with these things.
 
OK, I found a diagram of my clutch on the manufacturers web page. The shims are nothing but thin washers that come in .04", .02" and .004" dimensions. They sit on the compressor shaft between the armature plate and pulley/bearing assy.

So removing the nut and armature plate will give me access. I'll try to remove one of the shims and see what happens. Of course I'll take measurements and try to find the proper specification. For some reason it doesn't give a specification on the overhaul manual other than to say that it may be necessary to vary the shims until it works.

Thanks a ton for this tidbit of info. It gives me a direction to go.
 
In all of the places I have worked, we never put new shims in an A/C clutch. We replaced the AC compressor unit every time.
 
Yep, just pop out washers until it ALMOST touches.

I did this on a 340,000 mile Volvo 850. It went from not engaging at all to freezing my nuts off. On that engine it was pretty involved to get all the accessories off to get at the compressor, but very worth it. And cost nothing but time.

Of course a shop is going to push new compressors! Then they can sell a new receiver, x-valve, flush, condenser, then charge for an evac and fill. But it's completely unnecessary when there's nothing wrong with what's INSIDE the compressor.
 
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My truck is quite easy to work on. Once I remove the belt I have complete access to the compressor and plenty of room. I will have to make some type of tool to hold the clutch while I remove the nut though.

Artificialist, I suppose that if I were doing this job for profit I'd do what yielded the greatest profit for the least amount of effort. I'm certain it's faster to remove and replace the compressor but I have no way to evacuate the system nor desire to replace the receiver/drier once the system is open.

For what amounts to a afternoon of tinkering I could possibly have my A/C back to it's old, cold self with practically no outlay of cash. Of course this is all dependant upon this air gap being the problem.

If this doesn't repair the problem then I'll just replace the compressor and take it to a shop to have the system evacuated and refilled. I'm just trying to save some money and use a bit of mechanic skills.

Thanks again for the input!
 
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