Hi,

I have a 2012 C250 1.8L. The blower motor was making intermittent noise for some time until I started to see the blower speed jumping around when set to 'high' and eventually, I no longer have any function of the blower motor for HVAC.

I assumed it was the blower motor so I replaced it and still no success. I then used my multi meter to check voltages. I record 0V coming out of the blower motor resistor and into the blower, regardless of what the fan speed was set to one the dash. There is a 3 prong plug which plugs into the resistor (red, white, brown). I measured a voltage of 14V across the red and brown wires at all times. I measured 14V across the white and brown wires when the fan speed on the dash is set to high and as a lower the fan speed, the voltage reduces. If I turn the fan off, I record 0V across white and brown wires. I performed the same test using the frame of the car as a ground rather than the brown wire. Identical results. This all makes sense.

This led me to believe the blower motor resistor had failed. I purchased a new one and still no luck. At this point, I bypassed the resisitor and connected the blower motor directly to the red/brown wires that feed into the resitor. Both the old blower and the new one I bought ran perfectly. Once again, confirming to me that it is the blower motor resistor.

I find it unlikely that my resistor failed and I was shipped a faulty one as well. Do you think the issue lies elsewhere or do you think the new resistor I purchased was faulty?

Thanks for your help! This has been a cold winter in the car!