legacycentral bbs

94 Legacy SW 250t

When I've been driving around for a while and I turn of the engine, there is a knocking sound which eventully slows down and stops.

I've looked under the hood and its the compressor still turning.

Why is it doing this and how can it be fixed.

Thanks

I'm sorry to tell you that your compressor is probably on its way out. They usually start knocking when they've been starved of lubrication. Left that way, eventually they fail completely and send bits of metal all through the system.

It might be early enough that you could at least temporarily resolve the problem without replacing the compressor -- have the system evacuated, flushed, and recharged with new oil as well as refrigerant. Or be ghetto and try an "oil charge."

It's toast. There is nothing you can do to salvage it. It's already putting metal shavings into the system.

Just drive it until the compressor seizes. At that point, remove everything, clean it THOROUGHLY, and put a new compressor in.

I've been through 3 used compressors, and finally put in a new one.

What if the AC is not turned on, will it still "send metal bits throughout the system"?
At what settings is the AC compressor used or turned on?

If the compressor is not running, it won't cause any more damage than whatever's already happened.

The compressor runs in A/C, MAX A/C, DEFROST, and DEF/HEAT modes. You can disable it by disconnecting the compressor clutch or pulling the relays from the fuse box.

You can also wire in a "kill" switch to the compressor, so that when the Defrost is on outside air that is not chilled can flow.

At WOT there is an automatic shut off switch, but a manual over ride is a worhwhile option

can you just unhook the belt, or will that affect other systems, too?
I can't picture where the belt goes around right now.

just pull the relays for the time being, its a 1 minute job.

You can just remove the belt, but you may as well also electrically prevent the clutch from engaging.