Hvac Blower Control Module

knightgang · January 10, 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

JoJoJim · 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

JoJoJim · January 11, 2011

Shame on me but can't resist. My wife's Denali has the same system as your truck and by golly it had a resistor module in the plenum chamber -not part of the blower motor - but it does control it running or not running. Hers stopped working the same way and I thought it was the control the climate control etc wasted a lot of time and then simply had some good advice from this same web site that told me to change the resistor. Guess what it works. I apologize for violating your request not dare mention resistor.

knightgang · January 11, 2011

Shame on me but can't resist. My wife's Denali has the same system as your truck and by golly it had a resistor module in the plenum chamber -not part of the blower motor - but it does control it running or not running. Hers stopped working the same way and I thought it was the control the climate control etc wasted a lot of time and then simply had some good advice from this same web site that told me to change the resistor. Guess what it works. I apologize for violating your request not dare mention resistor.

Jim,

At least you understand that the difference with the Climate Control system vs set fan positions.

Next question, you said the resistor was in the plenum chamber... Where is that? I was told that there is no resistor on these AC systems, however if you changed on, there must be. Have have this dash board in pieces, if you can point me in the direction of this resistor, it might be worth a shot.

However, what really toys with my now is that if it is the resistor, why would it not work, then work with a new control head and new blower control module, then stop working again and the resistor was never touched...

Mind Boggling....

Thanks...

djmercer1 · January 11, 2011

Shame on me but can't resist. My wife's Denali has the same system as your truck and by golly it had a resistor module in the plenum chamber -not part of the blower motor - but it does control it running or not running. Hers stopped working the same way and I thought it was the control the climate control etc wasted a lot of time and then simply had some good advice from this same web site that told me to change the resistor. Guess what it works. I apologize for violating your request not dare mention resistor.

Jim,

At least you understand that the difference with the Climate Control system vs set fan positions.

Next question, you said the resistor was in the plenum chamber... Where is that? I was told that there is no resistor on these AC systems, however if you changed on, there must be. Have have this dash board in pieces, if you can point me in the direction of this resistor, it might be worth a shot.

However, what really toys with my now is that if it is the resistor, why would it not work, then work with a new control head and new blower control module, then stop working again and the resistor was never touched...

Mind Boggling....

Thanks...

bad connectors to eother the blower control module or control head maybe? is it possible that when you replace it you reset the connetor and it wiggled loose with a bit of driving?

JoJoJim · January 12, 2011

I think I can find a picture but it is a few inches to the left of the blower motor inserted from the bottom. It will look like a rectangular box that is hanging down out of the chamber about 2" X 1" held by two vertical screws and will have two sets of electrical cable connectors snapped into it. Easy to get to and remove. I know how frustrating this is as I tried everything to be the blower to work.

I will see if I can't find a picture and send it on.

Jim

JoJoJim · January 12, 2011

I am not having a luck downloading a picture of it but if you go to the web google and just put in 2001 1500 etc etc heater blower motor resistor with climate control. It will show several varieties but suspect yours will have a number of cone shaped prongs that stick up into the chamber. Mine cost approx. $65.00 at CarQuest and believe they supplied original equipment part. I see some less expensive ones but some are not the correct one for Climate Control models. Also I have heard it is a good idea to check the wiring going into the connectors as it frying the wires was a fairly common problem during that time period. I did not have that as an issue. Let me know if I can be of more help. If you want I can call and get a part number for you from my buddy at CarQuest tomorrow.

Jim