I have an '87 F150 with 4.9l automatic.

It mostly runs fine except it doesn't want to idle sometimes but that's not my primary question.

My primary question is what is causing the squealing noise when the a/c is on?

I've poked around with a stethoscope and it does not sound like the pwr steering, compressor, idler, or alternator. That leaves the fan clutch or the water pump.

It appears that the previous owner attempted to solve the problem with serp belt replacements since there were 2 with little apparent wear in the tool box when I bought it.

It also appears that I am losing coolant but I don't see a leak or have any dripping on the ground.

My guess is water pump but how can I be sure?

 

Sounds as if the compressor is locking up or trying to.

 

Thanks Jim. I'll check it again with the stethoscope But when I probed around the first time it didn't seem to making any noise.

 

I went back out and probed all of the turning things on the front of the engine with the stethoscope and I'm now convinced that the squeak/squeal is coming from the water pump.

The noise is definitely not coming from the tensioner, pwr steering pump, a/c compressor, or the alternator.

The air pump was in question when the noise was intermittent but when it became more consistent it turned out that the squeak/squeal was definitely coming from inside the water pump.

My theory is that when the compressor engages it puts enough additional strain on the belt to reveal the water pump bearings beginning to go **** up on me.

 

Before pulling or replacing that water pump, clean all the surfaces of the pulleys with alcohol. Normally a noisy belt like yours comes from oil on the pulleys and belt. Sometimes a new belt must be put on after cleaning the pulleys as the belt will absorb oil. A couple of bottles of alcohol are a lot cheaper than a new water pump....less than 5 bucks from Walmart.

 

Pull the serpentine belt, then spin the water pump by hand, does it sound like a bad bearing? Then, spin the smog pump pulley, is it noisy? Lastly, install the belt and start the truck, turn the AC on. Now, look under the hood, does the belt slip when the clutch engages?

That should help diagnose the noise.

 

If it's belt slippage, spraying it with water will stop the squeal for a short period.

 

Thanks guys. I'll work with your suggestions regarding the belt before I commit to replacing the water pump.