Manager Forum

Manual A/C with rear A/C.

We replaced Fr blower motor about a month ago. There does not seem to be any difference in fan speed between 4 and High. We have measured the amperage at the fan when the switch is moved and there is no change. Seems a no brainer. Replace the switch. Just to be sure we applied power to the blower with a probe and we cannot feel a significant difference then either. Now I am scratching my head. Oh, no cabin air filter, just so we dont go there.

What am I missing here folks?

First thing I am thinking of is a blower motor resistor failure. Dealer item only. Have seen a few of these fail over the years.

Doesn't it just bypass resistor on high? and why does it not blow harder when we apply power with the probe? That is what has me scratching?

It's possible that the blower resistor has failed in such a way that speed 4 is no longer a resistor but straight through power. If that's the case, then position 4 and 5 would be identical. To eliminate the possibility of a blower problem, substitute a load like a headlight bulb, then visually see if there is a difference between the two speeds. You should also check amperage with the bulb. If test results are the same, then it must be the resistor. There's a slight chance that the windings in the replacement blower are such that they draw the same with 2 different speeds. It's not likely, but the bulb will help isolate the issue.

HTH,

Ric

That was my initial thought, that the resistor failed on the fourth speed. But you bring up a good idea of checking it with a load.

tnx Ric and Tim... retesting now

I had a GM once that had failed in the past and some had by-passed the highest speed resistor with a connector and on next to high it was blowing same as high. Might be worth looking at.....

another little thing here. i've run into the plug at the resistor is melted internally and is shorting to power. also look at the ground wire where it attaches to the body. i've seen them slightly loose and the insulation melted back. a loose ground will cause an issue like this one.

Ah yes steve, I forgot about the wiring harness on them resistors. I usually replace them as well cause it seems they may be the issue, I haven't quite got figured exactly if the poor contact at the wiring harness causes the resistor to fail or how that is. They can be rather difficult to get.

Well... call me a monkeys uncle. The resistor was bad on setting 4 and was blowing on high at that point. I have not seen one do that before. Thanks for the help. Sometimes it is hard to get out of my own way.

thanks for posting the fix.