I have a 2000 chevy blazer. My heater is not working. I have replaced the thermostat cause that might be the problem but it wasnt. I have no idea what else it could be. Any advice would be very helpful.

 

Not working how? Does it only blow from the floor or defrost? Does it not blow air at all? Does it actually blow air from where you've selected or just has a mind of it's own? Is the air warm or just outside air?

 

Please give us more information on the issue. Do you have hot air at all ? Did you just buy this truck?

 

The AC works perfectly. When I turn the the **** to the turn the heat it you can hear it changing but no heat blows. Every thing else works fine. Could it possibly be the heater core?

 

Is the heater core connected? check if you see 2 rubber lines coming from the firewall on the passenger side.

If there is 2 aluminum lines sticking out with no rubber hoses then the heater core is disconnected.
Its possibly the bend door also.... Do a search on the forum the topic has been covered many times...

 

"bend" door is the blend door & I'd say back flush the system.
Grab the lines leading to & from the firewall (PS) - are they the same temp? If not - back flush the system.

On our vehicles ALWAYS check vacuum lines. Under the hood & to & from the cab.
If they're rotted/cracked you will not have control over where the heat is applied & the engine will miss/run crappy.

It could be a blend door issue as Gio said, but the free checks (no money & little to fix) are vacuum lines.
Sounds like a blend door actually. You can search Blend Door out in here for remedies.