Automotive Air Conditioning Information Forum

Hey all. I have a 2007 Chevy Trailblazer LT, 4.2L I6. My blower motor runs continuously, even without key in ignition. What possible issues could be at play?

The only blower motor resistor that I could find that would attached correctly was part number 4P1516 (this one has the female attachment that fits my male attachment). Is it possible that the wiring to the blower motor resistor is not the original wiring?

I have added a toggle switch to the ground wire for the time being (it is 100+ degree weather right now). Thank you all for any help/guidance and if there is any other information I can provide, then please ask!

There is also a blower motor relay in the circuit. Locate the relay, remove it and check the resistance across the contacts. When they fail closed circuit they do exactly what you are describing.

Do you have manual temperature control or the ATC system?

I will try that approach tomorrow, thank you. I have the ATC system.

The ATC units were 5 pin control modules. The manual stuff had 7 pin connectors. I know there are some aftermarket 5 pin units that come with a pigtail for retrofit - this could be why you had trouble finding the right part.

There are other differences as well. The OEM ATC units were solid state, with an aluminum heat sink on the back side in the air flow. Manual units had a block of power resistors (usually green ceramic) with two bullet shaped thermal fuses on the resistor bank.

Again, I have seen aftermarket solid state retrofits for the blower control module.

But the whole system is switched through the main relay, which is controlled by the ignition switch. So a stuck or welded relay is still the likely issue.

These were semi-common failures on 90s era GM vehicles that had automatic climate control. What would happen is that the central module would fail and you'd have a high speed fan all the time or none at all.

When we had a vehicle where you had to pull the fuse to turn off the fan, that's the common failure.