Hvac Blower Control Module

knightgang · January 11, 2011

2001 Chevy 1500 HD with Automatic Climate Control.

***Please note*** this truck has automatic climate control with a Blower Motor Control Module and it does not have a Blower Motor Resistor in it. Please do not reply with anything having to do with a resistor as they are two different animals...

That said. i am still having problems with the Blower fan not working. I have replaced the AC Control head and the Blower Motor Control Module. Before hooking up the module, I metered the signal from the new control head. Orange Wire, 12-14 volts as it should be. Black Wire, ground and has continuity as normal. Small grey wire, measured voltage was 0.01 volts at the lowest speed setting and 0.07 volts at the highest speed setting.

I figured, good deal, this thing will now work. So I plugged in a new Blower Control Module and measured the purple and black wires coming from it and got the varied voltage out (up to 12V) depending on the position of the fan switch. So, I continued and plugged up the module to the blower fan and everything worked great for a while, until I went for a drive...

Once I pulled out of my neighborhood, the fan motor stopped blowing. Here is where I cannot figure out what happened. I have retested the signals form the control head, no change. I am not getting any voltage out of the blower control module regardless of the fan speed setting. Again, the same signals tested earlier and still being measured at the lead from the control head to the blower control module. So, I figure that the module has gone bad again, but something must be causing it but I cannot find any chaffing, short or burnt wire anywhere in the truck, much less in a circuit that might actually affect this system.

I have taken the Blower Control module apart and examined it and cannot find any signs of failure. No burnt circuits, no busted resistors, no swelled capacitors, nothing.

So, to my actual question. What type of signal does that Blower Control Module look for form the Control head. Is it a variable pulse and if so, at what voltage? Is it a constant pulse at a variable voltage? Is it a set pulse at a set voltage with a variable frequency? etc....

I have a service department at my work that can test it if we know what type of signal that module is looking for.

Additionally, if anyone else has any ideas as to what is causing this issue, please chime in. This has not worked properly since May.

Thanks

gmtech4 · January 11, 2011

seems as though you have the wrong forum,you have posted in "ask a GM tech" forum

you are looking for the "ask a GM engineer" forum

sorry for your luck

PS,where is this "blower control module " you speak off?

alittle long of a post ,i had a nap while reading it lol

knightgang · January 11, 2011

seems as though you have the wrong forum,you have posted in "ask a GM tech" forum

you are looking for the "ask a GM engineer" forum

sorry for your luck

PS,where is this "blower control module " you speak off?

alittle long of a post ,i had a nap while reading it lol

Maybe an engineer is the ticket...

The Control Module is the the same place the normal blower resistor would be.

Hope you had a good nap. I have fought with this thing so long I just want to be sure everything is explained in detail to help get the right answers.