My 1994 Nissan Altima is a great little car with an unknown number of miles, though my best estimate is around 150k. Every time the air conditioner compressor kicks in it drags the engine down significantly when at idle, and often causes the belt to squeal. The squeal is most notable while accelerating. My question is, since the belt is relatively new do I have a tensioner problem, a compressor problem, or something else?
The problem might be caused by a dirty/defective Idle Air Control valve.
https://www.rockauto.com/en/moreinfo.php?pk=46790&cc=1210521&jsn=349
This component is mounted on the end of the cylinder head.
And what it does is, it controls the engine idle speed when different loads are imposed on the engine. Such as turning on the AC.
If the IAC valve goes to the wrong position for the idle condition, it can cause the engine to idle rough, stumble, and even stall.
What you can try is, remove the IAC valve and clean it along with any port on the head with throttle body cleaner to remove any carbon deposits. And then cross your fingers that fixes it.
Because the image I provided is from RockAuto. And you can’t get one from them for under $200.00
Tester
Normally I agree with Tester on most everything, but the fact that you are hearing squealing sounds points to a slipping belt. The tensioner could be getting weak but the compressor is probably causing a high drag too.
There is a test for the tensioner but mechanics time is not free. If you look at your belt and find the longest section between pulleys, push on the belt. It should take a lot of force to move deflect the belt 1". A 1/2" deflection should not be too hard, but the second 1/2" gets progressively harder as you approach the 1" deflection.
If that seems to be OK to you, then I think you may need a new compressor.
The belt should be able to deflect 1/2" . . . not 1"
or you could just use a belt tension gauge
On the AC-related engine loading, AC uses quite a bit of engine power to operate, so if there’s even a slight problem w/the engine performance it will be amplified in spades when the AC is on. Besides Tester’s IAC, other likely guesses on a car of that vintage I’d be looking for a vacuum leak causing a lean mixture, marginal ignition timing, faulty ignition module, spark plug wires, or distributor, spark plugs, clogged engine air filter or cat, or a clogged fuel filter or fuel pump on the fritz. Be sure to have your shop check for stored diagnostic codes for a clue where to start.