So first I would like to say I have been coming to this forum for years finding lots of information on issues i have had with 09 F150 Lariat and want to thank all of those that have help in troubleshooting those issues. With that said I hope this bit a information will help someone in the future or even now if they are experiencing what I went through.

During Thanksgiving I lost all control to fan speed, a/c, basically temperature control. After looking through this website I determined it was the blower motor resistor which many have had to deal with. Here is where it gets interesting on what happened after replacing the resistor with a Carquest Premium replacement part.

After replacing the after market (Carquest Premium part # RUA1031), part I got control of fan speed, temp setting (I have dual climate control) as well as zone control. Because it was cold enough here in Florida I did not turn on the A/C and i did not notice till about 2 weeks later. When i went to turn on A/C the light lit up but no a/c. Also no recirculation although the light lit up on the panel. After going through ever fuse, relay, solenoid, testing the climate control via pressing power and defrost (which when i did that i could hear the a/c clutch engage then turn off) even crawling under the truck and checking to see if the ac clutch was froze up or loose, i decided to start searching the forums for any information as to whether a faulty blower motor resistor could keep the A/C clutch from engaging. After 3hrs of searching I found an article which stated that yes a faulty blower motor resistor can keep the A/C clutch and recirculation valve from working. Although all the other functions worked, the a/c did not. The powerhead on the a/c is looking for voltage coming from either the blower motor or resistor or both to indicate that those devices are working as to keep the a/c compressor from running and just freezing the coils. I went to local dealership parts dept. and picked his brain about that scenario and he had never heard of that and asked me if I had tried all these other checks, which i had, so I went ahead and bought their part (Motorcraft Part # BL3Z*19E624*B), I pulled the aftermarket(Carquest Premium) and checked the resistance across the pins of the resistor. Ground pin 3 and check 1,2, and 4. all should be the same resistance and the aftermarket resistance were all the same 214kohms. I checked the new Motorcraft part and they were 1.9mohms....Huge difference. Plugged in the new resistor and bingo was his name o. So if i am correct then the aftermarket part was not allowing enough voltage to go through in order to send the correct voltage back to the A/C to say everything was ok. I took the aftermarket part back and let them know what I found and the guy behind the counter thanked me as he was just about to replace his motor blower resistor in his Ford and the sad thing is that the aftermarket and the OEM were the same price.

So, In short although some of the functions worked the resistor was still faulty enough to prevent all the functions from working correctly. I am glad i spent the time hunting the forums for an answer because i was dreading having to take it to an A/C repair shop and have them tell me the whole system needs replaced .

Again thanks to all those that have provided answers and fixes to many of my past issues and helping keep my blood pressure at a minimum.

 

Technically, what you have there is not a "resistor", it's an electronics module that is more accurately called in the service documentation the "Blower Motor Speed Control" module. Most retail parts outlets don't get the distinction and are too lazy to correct it. Actual blower resistors are used only in the manual climate controls.

It would be useful if you explicitly identified both the non-OEM part as well as the replacement Motorcraft part.

FWIW, pin 1 of the module is supposed to be ground. Pin 3 is supposed to be the PWM input from the DATC control module. Pin 4 is the HOT feed, pin 2 is the low side of the motor feed.

If the module's pin-out was incorrect or its PWM input otherwise incorrectly loaded down the signal line from the DATC module, it's entirely conceivable that the DATC's operation would be adversely affected to the point that other features malfunctioned.