My '99 Blazer won't put out any heat. It has the fancy climatic control system. The heater hoses get hot, so there's got to be hot water going to the heater core. Seems to me it has to be whatever regulates the heat from the heater core. How do I get in there to check this out?? Any help is greatly appreciated!

Mike

 

I believe that you have an electric temperature actuator ( in the most difficult place to access possible) on the top of the heater box, on the far right hand side.
I wonder if the heater core was ever replaced, maybe the wiring plug was not connected firmly.

If you turn the key on, engine off, can you hear the actuator working when you change the temp from cold to hot?

 

I can hear something working in there when I turn the heat control ****. I started it up and put the fan on high and had the air blowing out of the dash vents. When the temp control is on cold, it blows lots of air. When I turn the temp control to hot, it blows about half as much air as when it's on cold. The blower motor does not slow down either. Is there anything that regulates coolant flow to the heater core??

Thanks

 

Do you get any hot/warm air while driving around town or slow??

I had warm air flowing if I drove around town in stop and go traffic. A friend had an electronic temp guage and the vents were only putting out about 120* or less. But if I was driving on the highway the air would cool down. Plus is one heater hose hotter than the other either by touch or by gauge???

If one hose is hotter then you may have a clogged heater core. This is easy to fix. Just remove the heater hoses at either the firewall or if you want at the engine connectors (less coolant on the distributor cap). Get a couple of garden hose repair connectors and hose clamps for 5/8-3/4 in hoses (if you chose to remove the hoses at the engine), if you remove the hoses at the firewall then you might want to get some short length of heater hoses to use the hose connectors (this is what I did so I would have a "kit" if i needed to do this again). This will allow you to just screw on a garden hose to flush out the core easier with few leaks. Connect a garden hose to the outlet hose (one in the center of the firewall) turn on the hose until you hear a gush of water and it runs clear for a few seconds. Then reverse the connection a couple times to make sure the clog is cleared.

After clearing a clog in the heater core you will need to make sure that the water is removed from the core so you could blow through the hose with mouth on fist and your fist wrapped around the hose, to make sure as much water is out of the core, then replace the hoses to their proper connections and remove the radiator cap if it is not.

Now run the truck with the cap off until the thermosat opens (you see water running past the cap opening and all hoses are warm/hot, add coolant to the radiator until it is full, put cap back on and secure; do this a few times until you can not fill the radiator tank. Then check your overflow tank and fill it to the proper level for HOT and you should be done.



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I do recall that when I first checked it out, one of the heater hoses seemed hotter than the other. I'll try flushing the core out. I've got nothing to lose.
Thanks.

 

Hey all, I'm new to the forum, but am having the same problem with my 98 Blazer, I had great heat and now it seems to work when it want to! Here's what I know, engine temps seems to constant at 195 degrees at normal driving, the thermostat is new (and I did test before install, both heater hoses seem to be equally hot, coolant level is at correct level on overflow bottle. A couple of weeks ago it would throw heat when I stopped in traffic but as I would acellerate it would get cold again. I have turned off the engine and turned on the key and rotated the temp ****, I can hear the motor run to the heater box and I believe I hear a door open and close ( by the way you can hear this action better with the glove box open. My question is this, can you see any movement to that switch , to tell if it really is working? Also I understand there my be a vacumm switch to the trans that can fail, where is that located on the trans and can you test to determine if it is bad.
The best part to all this is my best friend's Jimmy started doing the same thing this week!!! Need help it's getting cold in Chicagoland!

Thanks for any help,
Al

 

The vacuum switch I think you are talking about is on the drivers side of the transfer case. It has three vacuum hoses attached to it. I believe it takes a 7/8 open end or box end to remove (open end better though).

On your heater issue it might be that the core has a blockage in it, just read the information in my reply earlier in this thread then you should be able to flush it...I have done this twice since I purchased my 2000 4dr. This last time I just flushed the whole system since it recurred within less than a year of fixing it the first time and I replaced the DexCool with Standard old green cooant, since the truck is out of warranty now I don't have to keep it in there and I want the engine to make it another 100k.

 

Thanks for the info on back-flushing the heater core, I tried it today and I now have the best heat ever......infact it's the 1st time I have actually had to turn it down, when I flushed it I saw some kind of "gunk" blast out at first then it ran clear, I let it run 5 min or so then switched pressure sides and ran it 5 min. from that side, blew out the water and reconnected the hoses, topped off with anti-freeze and I'm good to go!!! THANKS FOR ALL YOUR HELP......AL

 

That is what the forums are about (hopefully). But as with all things there are some forums that have better information and replys than others. I have found this forum to be the best for learning new things.

I think that most of the moderators and senior members have a lot of mechanical experience and knowledge. I myself have some background from my earlier years and from having a desire to learn. If you would like to find more knowledge check out E-Bay Motors Manual section they have lots of books and manuals on cars, I bought a DVD that contains service information from GM Dealers, this is where some of the diagrams/pics come from that I post with my replys if it is relevant...