1998 Park Avenue A/C quit

[rknorr]

I've got a 1998 Park Ave whose air conditioning was working fine when my wife drove it home for lunch yesterday when we switched cars, I got in and no A/C. Blower is working fine but the compressor is not kicking in. The compress clutch fuse is good and I switched out the relay with the other one like it and still the clutch doesn't engage. What next?

[Alibi]

How cold was the air blowing before? It is possible that you just don't have enough refrigerant for the compressor to remain engaged.

[rknorr]

A/C was nice and cold before. I checked and found the source of the problem, the A/C compressor clutch relay was not making good contact in the underhood fuse block. Once I pulled it out and reinserted it the clutch started working. The low side pressure is in the 55psi range. Thanks - Ray

[rknorr]

Apparently I didn't find the source of the problem, the compressor clutch won't engage again and reseating the relay doesn't fix it either. I tried swapping with the other identical relay which doesn't help. I know that both relays are good because car will run with either of them (its for the fuel pump). Any ideas?

[Alibi]

Ok, so the relay and refrigerant check out good. The next item I would check would be the compressor itself. However, if you have to remove it you would lose all your refrigerant and would need a re-charge, but I guess that isn't the end of the world.

At this point, I think you may be better off to let a shop diagnose it (especially to see if the compressor is any good) but don't let them fix it since you could do that for cheap.

I'm really no master at AC work, but maybe someone else has had this issue...

[HotZ28]

Originally Posted by rknorr

Apparently I didn't find the source of the problem, the compressor clutch won't engage again and reseating the relay doesn't fix it either. I tried swapping with the other identical relay which doesn't help. I know that both relays are good because car will run with either of them (its for the fuel pump). Any ideas?

Usually, the fuel pump relay is located in the fuse/relay panel under the passenger side dash, along with the fuel pump fuse. The one on the firewall next to the AC clutch relay, is for the horn.

What I would be concerned with here, is the "55 psig" on the low side, if that was tested with the compressor running and car cooling. That is not normal! You are either low on refrigerant, have a weak compressor, or a restriction in the system.

The 1998 Buicks have variable displacement compressors (V5), which will run continuously instead of cycling off and on. They have a swash plate, instead of a crankshaft to anchor the pistons. The stroke of the pistons, in this type of compressor, may be varied, from maximum to almost zero, by varying the angle of the swash plate.

These compressors usually have an internal mechanical arrangement to control the swash plate based on the suction (low side) pressure. They are usually set for about 28 PSIG. When the car is hot, the suction pressure will be much higher than 28 PSIG, so the compressor operates at full stroke.

When the car cools down, the suction pressure drops down through 28 PSIG, and the swash plate moves, reducing the stroke of the pistons, and lowering the capacity of the A/C, then the suction pressure will stop dropping and stay at around 28 PSIG.

The compressor will continue to reduce displacement by maintaining the suction line at 28 PSIG. If the car cools down too much, or if the sun comes out, and the car begins to heat up, the suction pressure will rise above 28 PSIG, and the compressor will increase it’s displacement, in order to bring the pressure back down to 28 PSIG.

Basically, the compressor will try to maintain 28 PSIG at all times, while it is running. At this point, forget the WalMart test & recharge kits and take it to a shop that has the proper test equipment.

[rknorr]

thanks for the info, I had no idea how this type of system works. The 55psi I mentioned was with the car running, A/C on but not warm at all. The pressure started initially around 70 psi compressor running and was working its way down in about 5 psi increments. I only had the gauges on it for a minute or two. Would you suggest a shot of R134a?

[HotZ28]

Yes, you can add some refrigerant and at the same time, watch the low side pressure. After you add some, give it minute or two to stabilize and test the pressure on the low side again. You could be just 1/2 can low. Do not put the whole can in if you do not need it. Place your hand on the low side line or drier/accumulator while the compressor is running. They should be around 34-38 deg. and feel like a cold brew straight from the frig. Your goal is to obtain 28-30 psig on the low side. If you set the controller on 60 deg. and the fan on M3, you should have vent temperature in the 40's, if you drive a few miles

[rknorr]

Okay, I'll give that a try within the next few days. I post the outcome. Thanks.