Recently my 01 blazer blower motor began to stop for a while and then, without any help on my part it would begin to operate properly. The Blazer has automatic temp control. I was about to order a new blower motor but my parts store advised to check the resistor. Since it has A/tc it is unlike the normal 4-position resistor. The type I have has 29 "****" protruding on its back side. Can this resistor be tested for resistance like the 4-position type? I can find no info on the internet except for the 4-position type. Any help would be apreciated.

usually, in Auto Temp systems, they use a blower control module instead of a resistor block.....

Thanks for the reply. You are certainly correct on the terminology. Now, how can it be checked for any "black spots". I have my doubts that this item is the problem. I believe that the problem lies with the blower motor itself. Whenever the blower quits working I am not in a position at that time to test whether-or-not it is getting current supplied through the control module. Can you give me any tips on checking the control module since my Haynes manual gives none?

Again, thanks for your original reply.

Well, first you need to determine which is the problem, the power or the blower motor.........this is auto temp, so you do realize when you are in "auto" mode, flow of air is not constant? Say it is set for 70 degrees, on a hot car, air flow will probably max, and then as the temp sensor senses you are approaching the set temp, air flow will slow down.....

However, if you go to manual mode, whatever you set the blower speed at, it should stay at that speed.....

So you need a test light......

manually set the air flow to a particular speed and stay in manual, not auto......if you lose air flow, then disconnect connector to blower motor and attach test light........manually move the blower from low to high.....the light should get brighter as you do this.......if no power, or spots with no power, then you need to check the circuits in and out of the blower module......if you have power on the test light through all the ranges, and the blower doesn't run, you need a blower motor....

I do have a test light and will try this the next time that the blower motor quits on me.

Keep this in mind as I have seen it many times.

The blower processor may light the test lamp properly which would lead to improper diag and blower motor replacement as the test lamp does not load the circuits as the blower motor would. Check the blower processor for water intrusion. I have seen plenty of blower processors with water intrusion that would light a test lamp just fine but could not handle the load the blower motor placed on the processor. If the processor has evidence of water intrusion, this is most likely the case. Happened on one of my vehicles, I opted to just change the processor and motor at the same time.

I've received your advice but I am a bit puzzled by your reference to a "blower processor." Are you referring to the hvac control module or to what I call the resistor which feeds the blower motor?

The blower processor he refers to is the blower module.....which is equivalent to the resistor block, if this was a manual system......

Instead of a test light, to create more of a load, you can use an old headlamp bulb/socket combination and hook it up.....should see it get brighter as you turn the speed up.....

The blower processor would be what you reference as the resistor. Use a headlamp as a load as Tech II said. Or better yet if possible, use a know good blower motor if you happen to have one available.

Your advice is appreciated. I will check into the blower processor as you have suggested before making any move toward replacing either it or the blower motor.