I first want to start with thanking everyone for many great threads that I've used in the past! So, as the title suggests, this is another "no heat" thread. I've read many old posts about various heating issues, but I can't really find my exact scenario.

I have the automatic climate control.

The heat was never that great in this Blazer, but it worked well enough. A week before this latest blizzard on the east coast, the heater died...naturally.

I reverse-flushed the heater core; a few rusty chunks came out...water was running through the core...no go, still cold air. (The Dexcool looked clear and clean aside from the rust that came out of the core).

The truck has always run pretty cool...about 160 by the gauge. So I grabbed a new thermostat...engine temp is spot on now, so I definitely needed a new stat...no go, still cold air.

Replaced the radiator cap for good measure...still cold air.

No leaking Dexcool that I can see. Never smelled coolant in the cabin, had a couple rear side windows fog up a little this morning, but no fog on the windshield. While under the hood, I can only touch the left hose from the core for a couple seconds; the hose on the right is pretty hot, but it is definitely not as hot as the left hose. When turning the temperature from cold to hot, I do hear a "click."

Obviously, I'm doing everything I can to avoid replacing the heater core, but my options are dwindling.

So, what do you guys think? My last ditch effort is to check the blend door actuator...not sure if the "click" is it working or if I should hear more of a door closing.

 

If one hose is way hotter than the other the issue lies in the core most likely. You could pull the hoses and make sure they are clean. What I did with mine was dump a container of CLR in and let it sit for 10 minutes, then flushed it in both directions. It came out black, and I have had good heat ever since.

 

Prior to installing the new thermostat, both hoses were relatively cool; I could touch them without feeling like it would burn my fingers.

After installing the new thermostat, both hoses are what I consider hot, but the hose on the right is slightly cooler.

I've read mixed opinions on using CLR; some saying that it's too harsh for the core...might try in a last ditch effort.

 

That is why you only leave the CLR in for a couple of minutes.

 

The temperature control circuit could have failed (the temperature control circuit could be commanding full cold regardless of the position of the ****), or the motor that diverts air through the heater core could have failed (it could have failed in the "full cold" position).

 

I got the heat working! I figured I'd post an update since the fix was actually accidental.

So, I've been having issues in the cold with the battery keeping a charge if the vehicle sits for more than 5-7 days. The battery was dead one morning, so I jumped it, and that's the first time I noticed there was no heat (I didn't mention this in my original post because I thought that it wasn't important).

Flash forward to this past weekend; I go to start it and it's dead again. Jumped it again, and let it idle for a bit. Sit in the Blazer and holy crap, the heat is working...it'll melt me now it's so hot (thank you new thermostat).

So, I suppose the first time the battery was dead and I jumped it, something didn't sit right with the electronics somewhere...

Anyways, no need for a heater core, so I'm super stoked!

 

Good to hear that someone gets "lucky"....