Blower motor resistor question

[DCAlden]

On my 2008 Astra XR the blower fan has only worked on high since I bought it a year ago. The previous owner had a gm dealer replace the resistor about 6 months before I bought it (I have the receipt).

I thought maybe they hadn’t replaced the cabin filter when they replaced the resistor so I decided to get a new ac delco resistor and cabin filter and replace them both.

Sure enough, the cabin filter was absolutely filthy. Probably never had been replaced. I replaced the filter and the blower resistor but the fan still only works on high.

Barring the posibility that the new blower resistor is bad, are there any fuses or relays that could be bad that would cause the blower to work only on high?

As you know, its a PITA to get to the cabin filter & resistor so I’m going to leave it apart until I can figure this out.

Thanks!

[AstraFasta]

You can test the old blower resistor with a simple multimeter to determine if the thermal fuse is open or is still good. Just check resistance around the terminals and it will be obvious where ground and increasing resistance terminals are.

You can do the same with the new blower resistor if you like.

Is the fan noisy? Even if it is not noisy, it is possible the cheap oiled bronze bearings in the fan are worn and/or there is a lot of debris inside the fan. So the fan draws more power thus blowing the resistor pack. The fan is fairly easy to remove and inspect inside for dirt and to see if it spins ok.

It is possible you have a wiring issue or an issue with the fan speed pot. I don't think those are the typical issues when your fan only operates at 4 but anything is possible. The DMM can help there also.

FYI - on our Astra, the fresh air door at the firewall was not properly installed at the factory and allowed water to drip into the blower motor. The water killed the fan bearings and one winter day froze in the fan cage, killing the blower resistor. This does not seem to be a popular failure but interesting nonetheless.

[DCAlden]

Thanks for the quick reply AstraFasta!

Ok, I checked the resistance on both the old and the new unit and they both read open circuit. I got the replacement unit off Amazon as “New, open box” for about $23.00. Im begining to suspect that it was a defective return. So, I’ve ordered a brand new unit for $85.00 and will try that before digging any deeper.

The fan motor is strong and quiet on high so it’s probably fine. The cabin air filter was packed with dirt, crushed leaves, dead bees etc. Why on earth the dealer did not replace it at the same time they did the resistor is beyond me.

Anyway, thanks for the suggestions. I will follow up after I have installed the new resistor unit and let you know what happened. Does anyone know the specs for the thermal resistor? It would be a very easy job to solder a new one into the old unit and have a spare one on hand.

[AstraFasta]

The specs are printed on the part for both OEM resistor packs I have owned. I might have posted the specs here but your parts could be different I suppose. I found 5 for a dollar at a retail electronics store IIRC.

BTW - You need heatsink the part very well when soldiering else it degrades (factory bonds it with a different technique).

Amazon OEM parts are getting more dubious over time. So may have been a fake, a defective unit, or a return.

Also, you can't be sure that fan is good. As you are having issues, check fan cage for debris and spin it for freedom. My brother had same issues with a different car; quiet fan was the cause.