I have a 98 xj with the 4.0 every time I turn the heat on especially when cold out I get a very loud squeal and the more gas I give it the louder it gets tilI warns up. I heard its a common problem but just need some answers. But when the ac is on I get NO squeal at all

 

Belt. Alternator. Heater fan.

Not sure if I would describe your problem as "common".

 

Tighten belt.

 

Try to pin point where exactly the squeal is coming from. Most likely loose/worn/glazed belt. Could be glazing on a pully too. Check belt condition and tension

 

I.ll check the belt and go from there

 

My 93 does this too only when its really cold outside, if i let the motor warm up first I dont get the squeal.

 

Tighten belt .....

 

use a proper belt tension gauge to verify tension

google: krikit II

 

Goodyear Gatorback. Tighten until there's no noise. No tighter. Will need to be re-tightened after a couple weeks. Done.