So I have a 2001 ex coupe and since winter hit, my car began to have a crazy squealing noise when I have my heater/ a/c on. It goes away when I get up to like 25mph or I turn my heater off. I've been reading and saw you can adjust the alternator belt. Would this be my solution?

 

The only noise the heater could possibly make is from the fan blower, unless you have the a/c on which is just stupid. Check the belt condition, tension, tensioner bearing and finally the compressor bearing.

 

What's weird though, is when it isn't making the noise and I turn on my rear defrost, it kicks the sqeal back on. Still the same thing?

 

Check all your accessory belts for condition and proper tension.

 

Hi there! I am having sort of the same issue. Belt would squeal something awful when I would turn my A/C or the defroster on. My battery light would also come on and the car felt like it wanted to die. I replaced the belt and now when I turn the A/C or defroster on, I get a much more rough noise. No more squealing, but it seems to me like the A/C compressor bearing might be going out?

 

A/C is generally installed for the purpose of cooling, but a by product of cooling air is the condensation of water vapour, therefore an air conditioner will dehumidify and I use mine for that purpose through the winter. It's also good for the air conditioner to be used from time to time during the months when you wouldn't use it for cooling to keep the seals lubricated.