Irregular cabin fan speed

[ShoogDoog]

Hello, all. I have a 2004 LS with 3.9L engine. When running the air conditioner, the fan speed changes radically, from off to high to medium and so forth; consists of random speed changes. Cabin air filter is new and visually everything under the hood looks ok. DCCV was replaced about 10 years ago.

I just got a code reader that I'm going to try out, so maybe that will provide a clue, but in the meantime, is anyone familiar with this? Is there a code I should look for?

Thanks,
Ed

 

[joegr]

It's probably going to be that your blower speed control is failing. Sorry...

2006 Lincoln LS Workshop Manual

 

[ShoogDoog]

Thanks, Joe. Well, that looks nice and simple. Based on your "Sorry" I'm suspecting that the dealership is going to enjoy this one.

 

[joegr]

Dealership, wow!
Yes, they will. Officially, the dash has to come out to replace the speed controller.

 

[SHORod]

A typical consumer-grade scan tool will not be able to access the sensor values for the various cabin and duct temperature sensors, but it is possible that you have a temperature sensor or two that is/are not reading correctly, causing the erratic blower speeds. The temp sensors are much less expensive and much easier to replace than the speed controller, so it may be worth finding a shop that can confirm the readings of the sensors before buying and replacing the speed controller.

-Rod