I Have a 1988 Fiero 2.5

My ac was great and blowing ice cold. When I floored it around a corner I suddenly heard a loud knocking coming from the right side of the engine bay. I turned off the ac immediately so I could hear the sound more clearly, but the sound went away as soon as I turned off the ac.

When I turn the ac on at idle the sound is not bad, but the knocking gets faster and louder as the engine revs.

The ac still blows cold, but I am afraid to use my ac. If anyone knows what the problem might be, or what I should test or check I would greatly appreciate it. This is my only car and rush hour traffic without ac is awful.

[This message has been edited by FirstFiero88 (edited 06-06-2014).]

Check all your compressor mounts for loose bolts/cracks, but most likely the compressor is making the noise internally, and the only fix is a new compressor.

Also, being an 88 it uses a single serpentine belt, so if the compressor locks up, you're not going anywhere. I'd avoid using it until it gets fixed.

I had a noticeable rumble when the AC was on. Everybody said it was the compressor, but it was just loose. One of the bolts was missing, another was barely hanging on. Hard to get at. Take the battery out or use a lift.

Thanks for the info ill check to see if the compressor is loose, and if its not order a new one.

The (working) AC on my 88 2.5 locked up one day with a horrible screeching of the belt when I turned it on. You may expect the same some day if it's making noises.
Fortunately, the compressors are easier to change than the ones on V6 cars (I've done both).

[This message has been edited by TopNotch (edited 06-07-2014).]

Correct me if I'm wrong (I have a limited understanding of A/C), but the Fiero compressor is kinda like an engine and our compressors have 3 pistons.

Borrowed from RWDPLZ teardown thread



If your compressor has a malfunction internally, it could seize up just like an engine. Maybe the knocking you hear is a damaged compressor.

-Mitch
Edit to add this cool illustrated video of the inside of a moving A/C compressor:

[This message has been edited by mitchjl22 (edited 06-08-2014).]

The compressor on the 87-88 4 cyl is a V5 compressor and completly different than the DA6 or the HR6 like on the 84s and V6 cars. it is a varible displacement compressor and works a bit different.
If it is knocking, it is bad. it could be the pistons in it or the clutch. usally they don't lock up the belt as the clutch will disengage. Hard to say with a knocking compressor.
If you get a new one get a new orfice tube and drier, always good to replace when doing A/C. you don't need the varible orfice tube as the compressor is allready.

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quote Originally posted by FirstFiero88: Thanks for the info ill check to see if the compressor is loose, and if its not order a new one.

Unfortunately if the compressor died it probably left pieces throughout the system and the other major parts will need to be replaced as well. Rockauto has kits for everything. The problem with replacing just one item is soon you'll be back to square one. Hope for loose bolts.