have the digital control head, I have changed out the blower control module, the new one worked for 3 days them symptoms came back. I am thinking it must be the control head, cheapest I found new was $127. anyone bought one from a junk dealer, and what was the cost?
ac fan speed changes by itself updated
- Thread starter davidaward47
- Start date
You might be wiser to offer more details on the symptoms that you refer to as "new one worked for 3 days them symptoms came back" along with the testing that you did as opposed to swapping in more parts. I doubt that the control unit is taking out the module... it is more likely that the motor is taking out the module as the motor is likely drawing more than the rating for the embedded "FET". Other things like poor connection (overheated) cause problems also.
further, "changes by itself" means what, in "auto mode", the speed changes as required to meet requirements.
further, "changes by itself" means what, in "auto mode", the speed changes as required to meet requirements.
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Mooseman
Moderator
And also, if you want to replace the control head, get a used one instead. A new one will require programming at the dealer ($$$). Get one from the same year truck.
Have you tried recalibrating the system? Pull the HVAC-B fuse for a minute, put it back and turn the key to the RUN position but don't start it. Let it do its thing for a couple of minutes.
Have you tried recalibrating the system? Pull the HVAC-B fuse for a minute, put it back and turn the key to the RUN position but don't start it. Let it do its thing for a couple of minutes.
Mounce
Member
Not sure about for the Trailblazer/envoys but for the full size vehicles like my silverado if the unit is in auto mode it auto adjusts the speed based on cabin temp vs desired temp trying to achieve the desired temp you set on the control panel.
I have done the calibration thing. I did buy a used control head from another 2007 trailblazer this afternoon after installing it same things happen; i had the speed control set mid range and after a minute the speed dropped down to barely any air coming out of the vents, a few minutes later it came back up to the set speed. I will do another calibration with the new (used) control head. thanks for the replies
Mooseman
Moderator
What does it do if not on auto mode? If you set the fan speed manually, it should hold at that speed no matter what. If you don't see the fan speed bars in the display, it's in auto mode.
Matt
Member
- Dec 2, 2011
- 4,023
Bud, you push the auto button to get it into manual mode, or you adjust the fan speed and that will turn auto off.
christo829
Member
I'm thinking @budwich called it in post #2. This is similar to what my girlfriend's Durango was doing. After replacing the resistor pack and connector (hers has an auto mode, but has a separate resistor pack), the pack died again after about two weeks. I replaced the motor/resistor/connector, and it's been good for a couple of years now. The original motor was putting too much load on the circuit.
Good Luck!
Chris
Good Luck!
Chris