Blower motor will sometimes not run at all or will change speeds in real time no matter what the fan switch setting is at. The back system operates correctly and the air temperature is cold for both front and back systems. I don't believe it is a resistor problem or the blower would run on high speed no matter what the switch setting. The blower relay switch seems to function normally under the hood. There are no strange sounds coming from the blower motor when it does run. The connection to the blower motor appears to be tight. I am unsure if the problem is related to the blower control module ($150) or the control head ($600).
My car has 100000 miles.
My car has an automatic transmission.
One sure way to rule out the blower motor itself would be to observe voltage while the issue is happening. If the voltage being fed to the blower motor fluctuates, the problem is on the control side of the circuit and possibly the resistor. Hire one of our mobile experts to swing by and test the electrical system and track down this bug.
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