I'm not getting any heat out of my heater. I worked all the switches to no avail. The deflector that switches from def/vent/floor works fine but the air is pretty much cold. I checked the hoses under the hood and one is hot and the other is notably cooler, which indicates to me that the heater core is dispersing the heat so I suspect that there is a blend door that somehow regulates the amount of heat that comes out (I never had an understanding of how they work). I found an actuator replacement thread but want to be sure that I am headed in the right direction before digging in. Is there a way to test that actuator and door for function or is the lack of heat the test? Can I see it work or not work by pulling the glove box out and looking at it?

Thanks for the help.

 

One heater hose hot and one cold indicates that you may have a blocked heater core. May be time for a garden hose flush. Another possibility is a system with air in it that needs to be bled, do you hear gurgling in the dash? The last possibility is as you suggest, the blend door. Lots of stuff and experts here on the last one. I would check the flow through the core first, but dont use mad pressure, you don't want to cause a leak.


George

 

No, it's not cold, it's just not as hot as the inbound one by several degrees but noticeable. I take it as an indication that the heat is getting dissipated by the heater core. I understand what you are saying though.

 

Update:

The blend door seems to be working, I can hear it when the temp adjustment is adjusted and everything is off and it's quiet plus I can feel the difference in air flow all the way through the temp adjustments. Next I am going to go with a partially blocked heater core. Any suggestions on good flushing agents?

 

Start with garden hose pressure in both directions. Go easy, the system usually only sees 15 lbs.


George

 

OK, thanks!

 

Well it would be useful for you to tell us what year Blazer and what HVAC system you are working on. So I looked up your previous posts and it seems you have a 2002. I'm going to assume you do not have the automatic temp HVAC (that's a much more complex system).

George was pointing you in the right direction.

Even on the manual HVAC which duct the air comes out of is controlled by vacuum, but the air temp blend door is electronically controlled.

First check HVAC Fuse 21.
Make sure air is coming out onto the floor.
Make sure the gauge is going up to approximately 195.
Make sure cooling system is actually full and that you cannot hold the heater hose going into the heater core in your closed hand. If it's not that hot coming from the engine, then there is little flow through the core.
Next actually take the heater hoses off of the heater core and blow through it with a piece of hose and your mouth. Water should easily come out the other side. You want to absolutely make sure core is not plugged because it is likely the repair is going to get a lot more difficult very fast.
Probe pin B of connector 3 (light blue wire) on the back of the heater control assembly (while still connected to the wiring) with a voltmeter. Should read 0V when set to Cold, 12V when turned to hot. If reads 12v and you have verified the rest, then the air temperature acutator has likely failed and will need to be replaced. Get ready to pull the dash out for access. It's on top of the HVAC module.

 

Looks like I was slow on the draw!!

 

It finally warmed up so I went out took it for a ride. Everything worked but the heat and the heater lines were pretty warm on the in side and a little cooler on the out side. I disconnected the heater core and blew through it backwards and some dirt came out but I was able to blow through it with some effort. I don't know how hard much effort it should take but it didn't seem like too much. I hooked the garden hose up and a cloud of dirty water came out. I flushed it then blew the water out a couple of times, water flowed well. Hooked it back up and it fixed it big time. I have major heat, not just a small improvement. I a greatly relieved that that cured it and the core doesn't need to be replaced.

Thanks for the help

 

If you haven't had your system flushed in a while, it would be a good idea to do so, to help prevent it from building up again.