98 Blazer heat on all the time, Any Ideas?

I have read some things on the net about a servo motor that controls the heat door, but no instuctions to fix it. This all started when I replaced the 4WD switch on the transfer case and left the transfer case electical plug off and tried to start. Evidently this caused a fault code because the 4WD wouldn't shift correctly. Removed battery cable and 4wd now works but heat is on in the truck all the time. I have read some treads were people have had this problem when changing the battery, but no real sulotoins were given. Any help appreciated. Burning up in Indiana!:frown:

Manual HVAC or Automatic climate control? Is the blower on all the time and you're not able to change the speed, or are you unable to adjust the temperature? Do all of the speeds work correctly? Does the air flow come out where it's supposed to according to the mode switch position?

Has Automatic Climate control. Everything works, fan cotrols except for heat knob. Stays hot all the time regardless of position on temp knob.
Andy

You can check the fuses, but that's about it due to the complexity of the of Automatic Climate Control system. There are 4 temp sensors, an electronic servo, 3 or 4 vacuum operated motors and a processor, along with a mile and a half of wiring and vacuum lines. A body capable scan tool is necessary to diagnose the system. Best to leave this one to a qualified technician with the necessary test equipment, tools and knowledge of how the system operates.

thanks for the advice!
Andy

If you have a body capable scan tool at your disposal, I can walk you through the diagnosis and repair procedures.

If you have a body capable scan tool at your disposal.

What is a body capable scan toll? Or was that a mis-type? Yes I have 2 scanners at my disposal and normallly do all my mech-electrical work myself, but his ones got me baffled. If you could post a procedure or any info that would be great.
Thanks,

A body capable scan tool is able to retrieve body Diagnostic Trouble Codes, (DTC's). They start with the letter "B" and are followed by three numeric characters, ie. B0416.

It was the blend motor! I found some more info in another place on this site. The plastich gear inside was broken so I ordered a new one. Thnaks for the help!

Ok,
Received the new blend motor, plugged into the wiring harness and it doesn't rotate when moving the climate control knob. I removed the RDO/BAt fuse like I read in the other post, but no help. Any ideas any one? I hate to have to take it to a dealer. TIA