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I drive a 2004 Chevy Monte Carlo and the A/C is usually fine. However, this car has gone through 4 blower motor resistors.

What happens is that, randomly while driving or when turning the A/C on (it will go out even if the A/C is already on) the A/C just suddenly starts blowing full blast. HOWEVER, if I turn the A/C dial to off, it only blows air (not cold or hot) and the resistor does not get heated. However, if I turn the dial to any of the settings, the resistor begins to warm up and the hot/cold air starts blowing.

When I shut the car off, the air continues to blow. The reason I think the problem is the resistor is because, in the past, when I have replaced the resistor, this problem is fixed. However, I am now sure this is a chronic issue somewhere else - but I cannot even begin to think where.

Also, should the resistor even be heating up if it were the problem? Am I replacing the wrong part? I would think that, if the resistor were bad, it would either A) Not pass the resistor and no A/C would blow OR B) Blow at high speed and completely bypass the resistor.

Because I know when the dial is at the highest setting, the wiring diagram shows that the current will bypass the resistance.

Can anyone give any insight as to what might be causing my resistors to appear (or really) go out?

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  • It seems GM has had this issue as I had to replace the one in my truck. Usually just replacing the resistor fixes the issue. If you are getting constant failures, I wouldn't know why, other than the ones you are purchasing are just not good brands (to include AC Delco branded ones if they continue to go out). I do not know of a way to bypass the resistor, though assume it could be done. The way the one in my truck died was the fan kicked up on high and continued to run even with the ignition off. I had to pull the fuse to stop it. Replaced it about a year ago without further issue.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented May 29, 2014 at 17:40

1 Answer 1

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Turns out the ignition switch was bad. It was causing the blower motor to stay on even when the ignition was in the "off" position. Fixing this stopped the car's blower motor from running when off, then it was as simple as replacing the resistor once more and haven't had any problems for months.

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  • Just for future reference... when a resistor heats up, it passes LESS current (becomes "more open"), which means that a hot resistor will slow the fan down instead of speeding it up... and when a resistor fails, it always fails "wipe open" (passing no current at all).
    – TDHofstetter
    Commented Aug 14, 2014 at 2:25

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