Heater Issue? (99 Z)

[Papagoose]

Hey guys, got a question about my heater. My AC will freeze you out of the car, but my heater will not blow any hot air at all. Since my only book is a haynes (which only covers removal and installation) what are some probable causes? Do these things have one of those flaps (like on my ex-wife's 01 ford van) that will ease off on the heat when it gets over a certain temp so as to not fry the electronics (I have dealt with that situation before, so it was the first to pop into my mind)? some troubleshooting steps would be much appreciated, as the cold season is fast approaching, and this is my daily driver. Thanks!

[chevymec]

Check your coolant level . If its low you could get a low heat problem.

[Papagoose]

Level is fine, I know to check that much at least. I meant like anything else before I go straight to saying it's the core.

[chevymec]

Can you tell a difference when you changed the temp from hot to cold. The force of air should drop when it goes to heat. Also you could remove the heat hoses and try to flush it out.