Auto climate Hvac controls and blower

dla442

Original poster
Member
Mar 31, 2012
249
grand rapids, mi
Recently replaced the control module of the blower motor. Occasionally our trailblazer will have some symptons. The fan blower will not come on and visually appears all should be working fine. If i turn off the hvac off with the power button at the control head and turn back on, sometimes the fan will turn back on at what ever speed it is currently set at. Sometimes I have to pull the fuse(under rear seat) and the auto hvac system resets and the fan will work. curious if the control head is going bad? At over 200 bucks, I hope not. Just thinking the odds of a bad motor on the blower are slim given the symptoms. BTW, glad to see you on this site roadie
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Hi! I'm glad to be here, too! The old lifeboat was getting pretty leaky. :wink:

So why did you replace the module? Similar symptoms or did it die totally? Do you have a meter and want to dig deeper and not shotgun it? Control heads are going on Ebay for $50-100. No need to spend $200.

My first guess is the connector at the blower motor harness or the blower motor ground. If the blower comes back on at the same speed it was before it went out, it's less likely to be a bad control head.

silvernclean said:
There are more than just one fuse for the hvac. Just sayin.
Saying the numbers of the fuses would be more helpful. :confused:

Edit: Front fuse #35 (40A) runs the blower on the automatic system, assuming the control module is running well using the HVAC fuses under the rear seat.
 

jrSS

Member
Dec 4, 2011
3,950
39 and 44 in the bcm.
ad6de943-8ba2-1398.jpg
. :biggrin:

Its a 10 amp and 30 amp fuse.

ad6d7dae-8d5e-577a.jpg

The 2 fuses directly above my finger. (Looking at the bcm thru drivers side rear door)
 

dla442

Original poster
Member
Mar 31, 2012
249
grand rapids, mi
thats the fuses that were in the picture. The old module just plain died and had to be replaced with newer 5 wire module and has been no problems since except for recently. The fan just wont work, all vents do switch when promted. When the hvac is turned off and on(sometimes takes three times then restart the car) the fan works and blows. Its intermittent at best and hard to track down. before the module went bad, the rear seat controls froze up and the fuses had to be pulled to reset the system. Thats the best I have to offer. Connections are tight but I will check them again at the module. When it happens again I will attempt to use a meter to check for voltage before the module at the harness. Any other suggestions? Thanx
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Thanks for the background. Check the voltage at both wires at the blower motor if possible, with the other meter wire going to a good ground. Might be an intermittent
ground going to the blower motor.
 

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