For some reason my heater stopped working. It just blows out cold air when the heat is on. Any help is appreciated. 2004 Blazer 4x4

 

Has your coolant system ever been flushed? If it has had the dexcool in it and has been exposed to hear it is more than likely clogged the heater core. I would suggest flushing your heater core and seeing if that helps.

 

I'd check the vacuum lines - all of them. Do the vents work? If you switch it from floor to defrost does it actually switch? If not then it's probably a vacuum line cracked or off or the blend door is buggered up. You can search in here for more on them.

 

I would check the blend door actuator first. This is a motor-driven actuator tucked away behind the glove box. Check out the DIY section to see how to find it:

https://blazerforum.com/forum/tech-a...-method-69608/

 

Had the same problem on my 2001 LT. I flushed the system and got rid of the Dexcool and went back to the old green anti-freeze. Heating system working fine.

 

I believe it is the blend door actuator. Thanks for the DIY thread aa21830!

 

Yeah that's what I said. Vacuum or blend door.
Search is an easy feature everyone has to be coached into using.
Always easier to ask when in doubt, but in this day & age almost anything is available by searching around & learning.
Could be electrical to the door, could & more often likely mechanical at the door. Check out the local wreckers, phone calls & see if they have similiar years etc, just in case you need a blend door mechanism... prepare, have options & things lined up - just in case.

I'd bet good money that 70% of blazers from 2nd gen & certainly 1st gen have vacuum issues if they're unchecked.
From my experience here for HVAC issues vacuum issues take 60 - 70%, blend doors are 30% & electrical finish it up. Especially the canister in the fenderwell or "ball" hanging under the hood.

 

Well, I replaced the Blend Door Actuator and the air is still cold. Like Rottidog said it might be an electrical problem. I'm going to try to flush my coolant system first and see what that does.

 

please let us know how it goes. i have a similar issue with my 2001 4WD LS. When I have the heat on sometimes it kicks on, other times no air (or really faint air) comes out.

 

That DEX-COOL antifreeze is the devil!!! Thoroughly backflush your heater core, and while you're at it flush the entire cooling system and replace it with the green stuff.