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HVAC Fan - Works Ignition on but not with engine running
The HVAC blower in my car had been making a chirping noise on all speeds but high (7) for a few years and finally died yesterday. I picked up a replacement 'four seasons' brand as it was first available and came with a warranty. I swapped the fans out and here is where it all get weird.
With my ignition on but engine off, the fan works on all speeds without any issues or difficulty.
With the engine running, I have no fan at all. I can change the speeds but there is no response from the blower motor. If I turn the car off and put it to ignition on the fan again works perfectly.
Anyone have any insight? My thought would be that the resistor module is fine as I have all the speeds available when it works, I don't understand how the engine running would change the power source to the HVAC blower.
Last edited by SilentSmith; Mar 1, 2023 at 03:53 PM.
A thought is to check the connections against the old fan, make sure it’s wired the same and pins actually connect. It’s probably Chinese made . If it doesn’t work get one from a reputable company like FCP Euro.
There could be an odd failure in the new fan's circuitry ("regulator") that prefers 12.x volts to 14.x volts (failing over some threshold voltage in between). You could probe the connector to find out if the 12 volts (or even the ground) disappear when you turn the ignition on.
The HVAC blower in my car had been making a chirping noise on all speeds but high (7) for a few years and finally died yesterday. I picked up a replacement 'four seasons' brand as it was first available and came with a warranty. I swapped the fans out and here is where it all get weird.
With my ignition on but engine off, the fan works on all speeds without any issues or difficulty.
With the engine running, I have no fan at all. I can change the speeds but there is no response from the blower motor. If I turn the car off and put it to ignition on the fan again works perfectly.
Anyone have any insight? My thought would be that the resistor module is fine as I have all the speeds available when it works, I don't understand how the engine running would change the power source to the HVAC blower.
Agree with “weird.”
The blower motor, resistor, and controller are probably okay because they all work with the key on/engine off.
Maybe a high end scanner that can read HVAC codes would show something useful.
Last edited by Odd Piggy; Mar 3, 2023 at 02:49 PM.
Reason: Remove incorrect info.
Many of you might have seen I had similar trouble with mine and solved it all by swishing it in an alcohol bath to rinse off the carbon grit that came from the motor brushes. Fixed everything. I also saw an inductor that was * very * close to the motor frame with carbon all over it, so I pushed that over a ** tiny ** bit so it had no chance of touching a ground.
Just make sure to thoroughly dry it for quite a few hours before reinstall - alcohol is quite flammable.
The dealer also did this in a Smart car recall- they had the same issue in those fans, but didn't do an alcohol wash.
I finally chased down the schematic for the GLK, and (happily) the MB engineers did seem to do the traditional thing. ;-) Sometimes they can surprise me (though I doubt as much as the BMW engineers can). ;-)
The battery, alternator output, and starter are all tied together at the "main battery buss", which is typical since it's very difficult to fuse these items without causing a whole lot more problems than you are potentially solving. I do think there's a pyrofuse inline with the battery, though that only comes into play after a serious accident, and won't affect anything at all until it's blown, then nothing will work (due to the fact that the battery is now disconnected).
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