https://blazerforum.com/forum/showth...ferrerid=44375

My 2001 Blazer with a climate control computer has the same problem as the attached above. The heat only works when the temperature control **** is turned full clockwise past the click for the continuous heat position and then the heat is continuous and it is way above too hot in the cab.

I took out the module and there is a (30) terminal plug attachment. Is there a thermocouple, sensor, temperature bulb or thermostat somewhere else in the cab to which the computer module attaches and senses the temperature?

Thanks!! Richard

 

The cabin air temperature sensor is located above the driver's head in the headliner. It is behind the small grill. If this has somehow failed causing the HVAC control module to think that the temperature is already quite high inside, then the HVAC control module would respond by doing what you are describing. When you put it to max heat, it will always put out heat, but on any other setting, it is in automatic control.

I believe that there also is a plenum temperature sensor under the dash, but do not have the time right now to look up it's location. If this were limiting out high, it would also cause the system to cool.

 

big thank you
I will check it out and report back

 

I removed the sensor and it appears solid state and not serviceable. Only choice would appear to swap it out with another. Any suggestions before going that route? Thanks!

 

It is possible to test it's resistance based on air temperature, however I do not have the specs in front of me nor will I have time to see if I can find them anytime soon.

 

Hi, did you ever get the "hi heat only" issue resolved? I'm having exact same issue. Replaced blend door controller, tried donor dash unit with same result. Did remove Rad/Batt fuse for 1 minute, reinstall, turn key, and blend door mechanism does fully cycle. Stumped in California.

 

My problem was solved by replacement of a small dime sized switch located in the headliner above the drivers seat. I just grabbed one at the local boneyard. It was a very easy fix. Good luck!

 

Thanks for a "resolved" post. That's next on my list. I did try and clean it yesterday, was very dusty but didn't do the trick. Getting one tomorrow, pull the headliner down a little? Did you loosen the seat belt pillar plastic?? I get too impatient and break stuff. Thanks for the response Svensson and I'll let you know my outcome also! David

 

Cleaning did not work for me. I remember just nudging the fabric without taking off the pillar but that may just snap on or be a screw or two. No need to rush through it. Just walk away if your blood pressure goes up.

 

Got the cabin ambient temp. sensor today, peeled back the headliner and got it out, new one in, and....same as before. I have an external heater box motor switch I can watch, same one that goes on top of the heater box, and sure enough does nothing until you clik it over to Hi hot. Then turns all the way. Any ideas would be great! Thanks in Ca.