rpm issue when a/c comes on

[larsen101]

i have an 87 2.9 and when just idle its around 1000 rpm but when i switch on the ac the rps drop to around 700-800 and runs rough for the few seconds that the clutch is engaged. im just not to sure if this is just normal of if there is some kind of problem that can be fixed.

 

[srteach]

Check vacuum lines. A vac loss could cause the engine to keep a low rpm under load. It should run at the same rpm, with maybe a small rpm dip at first.

 

[WTF]

Is your a/c compressor original? Could be time to replace it if so.

 

[larsen101]

ok i will check out the vacuum lines and see about that. yes the compressor is the origional, still works good and puts out cold air. what would changing the compressor do, just run better or are the new compressors better. how much for a new one? also would this be caused by the tfi? not to sure just spit balling.

 

[WTF]

Well, if the compressor is worn out, it'll put a lot of drag on the engine and pull on the rpms a bit. I was actually the one spit balling. I guess the belt would slip before it would stall out the engine. Could be a voltage problem since it does what it does when your a/c clutch engages. I believe there's supposed to be a slight "rpm boost" when you do turn on your a/c. Could be wrong. Hope this helps!!

 

[gaz]

A/c should add a load to an idle engine

"larson 101",

It is completely NORMAL for the engine to drop some from IDLE when the A/C is energized as it is powered directly from the belt that spins the crankshaft. So by turning on the A/C, you are simply increasing the static load on the engine, its reponse is increase load @ idle and the engine RPM will lower do to the increased load.

I am not telling you that there isn't anything wrong with YOUR engine or A/C system, "from my magic ball"; just that my engine does and always has done the exact same thing when the A/C is turned on.

Kevin

 

[larsen101]

ok thanks everyone. hopefully nothing is wrong but im going to look into it some more and check out some things you guys said