2009 Lariat.
My AC and Heat both work but about a week ago they started to be almost non existent and despite me using the auto setting they will go from low to max for about 2 seconds and drop back down to almost off. This goes on for my entire drive and it doesn't matter If I turn the **** to 60 or 90, same effect.

So I tried to research the problem myself first and I came up with "motor resistor control"

Most of these posts are usually about the fan being stuck on high but would this same part be the culprit for what I am experiencing as well? I'd hate to buy a part that I don't need. Thank you

 

If your truck has the automatic climate control, you do not have the resistor module which is used to vary the blower speed. You have what is called the "blower speed control module". If you have the dual zone system, it looks like this:


Now, I don't if if it's your problem or not, that's what troubleshooting is for.

 

Well it's a good start, thanks for correcting me on the part. I'll grab one and try it out. Probably just going to order it online so I'll check back in roughly a week when I get it to me and installed to see if that did the trick.

 

probably should get one with the wire as well. The one in my Expd went and fried the wire as well.

 

I have the same problem ... was that the fix for yours ?

 

I have a 2006 F-150 with what could be a related issue. When it is hot outside in the say around 90 degree range and the vehicle is sitting in the sun the blower fan will not come on either on heat or AC. If the vehicle is moved into the shade and or has been sitting overnight and the outside temp is much cooler the fan works fine in both AC and heater modes. This seems to be some kind of sensor issue and which sensor would cause this issue.

Thanks