Weird AC fan issue?

[sjwelds]

So on my 08, the other evening we were in town, and all of a sudden the HVAC fan started acting up. It would go from low to high speed and anywhere in between at random. After a few more days of driving, I have observed the following traits.

1. It seems to only occur at startup and shortly thereafter.

2. It doesn't matter if the fan is on the "auto" or manual setting.

3. After a few miles of driving, and things getting to normal temps in the cab, it seems to work fine.

4. However, it makes no difference if you turn the engine off and restart it, it still seems to malfunction for a few minutes, even with a warm engine/ cooled cab.

Thoughts? Seems like if it was a connection it would be all-or-nothing, and also wouldn't go away after some driving....

 

[stamp11127]

Run EATC diagnostics, I would expect a code for the fan control module.

 

[sjwelds]

Ok, guess I'll reveal my newbness. How do I do the eatc self test?

 

[bloodhound]

Blower motor resistor on its way out is my guess. Do a search here. Very easy to replace if that's what it is.

 

[sjwelds]

Ok did some more research online and found out how to do the self test. No codes found; the entire display lights up, which I understand means no codes. Will do more reading on the blower motor resistor. Thanks

 

[stamp11127]

Manually controlled systems use the blower motor resistors.
Systems with EATC use a control module.

 

[sjwelds]

Would the control module going out cause these symptoms? Would it not throw a code?

 

[bloodhound]

Manually controlled systems use the blower motor resistors.
Systems with EATC use a control module.

My 09 has EATC and had the problem he is describing. Swapped out the blower motor resistor a year ago, perfect ever since.

 

[sjwelds]

Yeah, but are you sure we aren't all talking about the same thing? Isn't it even in the same location, just a different part, based on whether EATC or manual controls? My reading on different forums leads me to believe this. So stamp calls it the control module, bloodhound calls it the resistor, but we all know what we're talking about.....

 

[stamp11127]

Two different parts. Easy way to tell - the resistors are mounted so that the blowing air cools them inside the unit. The control module is mounted on the right side exterior of the HVAC unit.

Wiring diagrams show resistors with the correct symbols for the manual controls. Electronic modules are shown as a box without internal detail. The diagrams for your year is a box.

There is only one wire from the HVAC EATC to the module, two wires to the blower motor and one for ground.

The rear system uses the resistors.