michail71

I'm trying to determine if this is normal but the blower in my AC system seems to sometimes run erratically on initial startup. Today I had it on Max AC. At first it fired up to full power like it normally does and then the blower cut all the way down to low. It ramped up and then back down again for about a minute before going back up to the the Max setting.

Once it came on it cooled the car quickly.

It has done this at other times while on the Auto setting. I had thought it was just the sensor getting confused but Max AC should just run at max.

Plutoe

It's not a sensor----it's the fan rheostat that is faulty---remove the fan and replace the rheostat

michail71

Thank you, it's still under warranty so I'll ask the dealer about it.

MDMercedesGuy

Mine does this as well - always has since new, and only on super hot days.

It seems that it is doing some sort of calibration or such. It's consistent when it does it/how it does it and for how long, so I'd doubt something is faulty.

michail71

Yes, it does it when super hot. It's almost like it's teasing you.

crater64

I had the same thing happen with my car last week. Coming out to a big paved parking lot and finding temps > 100F after 5pm, the unit would "hunt" to find the right fan speed to deliver max cooling. We've had days ~ 100F here before since I've had the car, and this was the first time it had done so. It happened again twice later that week.

This past Saturday I had my car in for its second Service A (27K miles on odo) and described the problem to the service rep. The diagnosis was a faulty blower resistor and motor assembly; both were replaced under warranty.

Was this a necessary repair, or a case of the dealership creating some warranty work for itself? I don't know for sure. Our local weather forecast call for highs above 95F for the next four days, so we'll see what happens.