squealing noise

99/ Explorer LTD. 4.0 L when I turn on the A/C a loud squealing noise comes from the engine area. Also tried the heater and the same thing happens. Shut them off the noise stops. Only had vehicle 4 wks. new alt. installed just before I bought it.

thanks to all in advance

I could be the serpentine belt, or the A/C compressor going bad!

Mike

that alternator could also be the problem check to see if it was remanufactured. the bearings in the alternators can go out and you will hear it under a load (an electrical load) that fan for your heater and your a/c draws a lot of amperage. the belt on the alternator could also be to tight (putting more pressure on the alternator bearings. if its a remanufactured alternator they could have gotten into production with bad bearings. if you really want to tell you need to pop your hood and turn your a/c or heater on and listen for the noise. try pinpointing the noise with either a stethoscope (availible at autozone for about $5 or a long screwdriver held to your ear (the handle side) and the bussiness end on the part you think the noise is coming from. this should pinpoint the problem