KDuniverse

Just started the other night, and have not had a chance to look at the car until later today. When I start the car and put the AC on, it works great, then a few min later it's like the compressor turns off and warm air comes in. If I leave everything on, it will come back on. Sounds like an electrical issue...but where should I start? The compressor is a few years old, and the system was recharged last year. I hooked up a gauge and the charge is still good. Any ideas?

KDuniverse

clutch still spins very slowly when compressor is not engaged. what does that mean exactly?

0Paul Ruggeri

Sounds like the clutch might be dragging a little. Start the car and turn the AC on. When it stops working has the clutch disengaged? If so check power and ground at the clutch connecter.

KDuniverse

Figures, had the car running for 30min, and the ac worked fine, just now noticed the clutch slipping.

0Paul Ruggeri

Is the clutch slipping or is the compressor locking up. Is the compressor hard to turn by hand? If its OK, you could just replace the clutch.

KDuniverse

I think the clutch is slipping since it spins very slow when the AC is off. Would that make the air cold, then warm while it's running? Are there rebuild kits for the clutch?

0Paul Ruggeri

If the clutch is spinning when the AC is off it means the clutch is dragging. There are no rebuild kits, you just replace the clutch. You need to determine what's happening when the AC quits before you start replacing parts.

SunCr

NAPA sells individual parts including a pulley bearing, but it's easier just to replace the entire unit. Check the air gap between the outer hub and pulley, should be .020 inch. Check power and ground. Some of the electronic units (through '89) always supply power so one wire would always be hot and a coil shorting to ground could make it spin or appear to slip even when off. You also need to check operating pressures.

KDuniverse

will check this during the week. thanks guys

KDuniverse

Ok, so if I don't have the .020 gap there, what's my next move? What is actually happening here?

0Paul Ruggeri

There are small shims, like tiny washers, behind the outer clutch plate. Remove the nut holding the plate on, you'll see the shims where the stud is. Add shims to increase gap.

KDuniverse

What would the reason be for this to happen all of a sudden? Shims wear out? Or is there another issue here?

SunCr

They shouldn't wear out - unless someone went to Home Depot and found replacements that looked about right (hard to blame them since the 3 or 4 measly washers in the kit are 12 Bucks). Then the cheap tin alloy gets crushed and the air gap goes away - or someone overtorques the shaft bolt and crushes the shims during installation. Anyway, on these units, it's usually the gap getting wider from wear on the face plate and pulley. Other Harrison compressors, with a press on assembly, seem to lose the gap when driven off of the Dealers Lot, but not these Nippo's with a bolt holding the face plate. I would make sure that it doesn't have a leaking shaft seal - check for oil on the hood above the compressor.

KDuniverse

So I guess what I'm trying to figure out is why this is happening. Or should I just replace the entire unit?

SunCr

Kinda of a tossup - with out looking at it, there's a chance it's something else.

KDuniverse

So I finally had some time to work on this. It's just been too hot to do anything here. Anyway, changed out the clutch, and started the car. Worked great. Later that day I took the car out for the night, and it did the same thing about a mile down the road. What could this be now? Any suggestions on what to check?

VETTEHIGH

I had the same problem and it turned out to be:

($15 NAPA) Air Conditioning Cycling Clutch Orifice Switch

KDuniverse

any way to check that? is it in the fsm?

SunCr

I think the reference is to the Low Pressure Switch which is mounted on the Evaporator outlet - big tube on top. It opens at 25 psi which breaks the circuit to the compressor. It's there to prevent the Evaporator from icing up and/or the compressor from running when there isn't enough gas to carry the oil charge. Whether or not it reaches the cutoff threshhold is also dependent on the outside air temp. The only viable test is with a Manifold Gage Set (preferably with an air temp above 70 degrees). That will allow you to observe the Low Side Pressure with the compressor engaged and with the system on Max, disconnecting the Blower Motor will drop the Low Side and the Compressor should cycle off at the threshold or 25 psi. You could also disconnect the harness at the switch and jumper the connector terminals with a paperclip. That will keep the circuit closed and the compressor running - though if it's low on gas you will, at best, get a bunch of ice on the Evaporator and lines and at worst, blow up the compressor if it doesn't get enough lube and/or pop the relief valve and spew gas all over the place if the high side is backed up - so if you do this, don't do it for more than a couple of minutes.