Hello everyone. I've got a 2009 F150 Lariat XLT 4x4 5.4L.
My truck has the Auto Temp Control Dual Passenger system with heated seats only.. I lost control of the Blower Motor. Always on High Fan. Then fan quit working all together. I replaced the Dash control unit after checking all fuses #15 passenger side fuse panel and all relays for blower motor and HVAC system including AC Clutch, NO JOY. I then replace the Blower Motor Speed Controller. Fan started working, but on High again "without" control of it. At same time AC Clutch would no longer engage. For ****s and Giggles I replaced the Blower Motor. NO JOY. At this point, I'm out of ideas and super frustrated. There was a thread on this issue but no-one has found a fix or at least posted one. Please help. Retired Navy 20 yrs as an aircraft mechanic and disabled. Really need some help in this one. Thank You All...

 

Did you replace the blower motor resistor?

https://www.tascaparts.com/oem-parts...00bC12OC1mbGV4

BLOWER MOTOR RESISTOR - Ford (3F2Z-18591-AA)

 

The auto climate control AC system doesn't use a resistor, it Pulse Width Modulates the blower motor. OP I've replied to a couple of other threads on this very subject just in the last week. Did you find and read those threads? I think one is posted that OTHER F-150 forum. I'll look it up and post the URL here. There are three different fuses and IIRC two relays that control that system.

 

Yes I did. It's called a speed controller now from what I understand. Bolts up to air box with a 4 pin straight connector. It has 4 aluminum fins that go into air box. The inside is a circuit card with the 4 pins that go into the connector housing. After I changed it out the fan would come on real high and then slow slightly after 2-3 seconds. Also the AC Clutch wouldn't engage. AC compressor and clutch were working fine just prior to blower motor quitting. Changed speed controller as I said and fan began to work again as described above. Really scratching my head over it. I'm wondering if perhaps there are any temperature sensors in the system for auto temp, hi temp limit, and temp anticipator. I worked on aircraft air conditioning and we had sensors such as these. I wouldn't know exactly where they are and which ones do what as I have no schematics etc. Thank you for responding. Very much appreciate it.

 

Oh yeah, the auto climate control system has a ton of temperature sensors both inside and outside of the truck! I think the AC compressor is controlled directly by a manually operated switch but I'll look again.I know that one of the other people that is having problems with his auto AC system is also complaining that the compressor is off but we haven't figured out why. He changed his control module twice and IIRC the fan now runs on high (only) but the compressor is still off.. I've speculated and wondering if he has a bad module or the wrong module. It's strange that replacing it seems to have fixed part of one problem but not the compressor problem.

I really hate computer controlled devices where they don't tell you how they operate or how to trouble shoot them! Glad my 2010 has the old fashioned manually operated system.

 

So far I've changed dash control unit, part number matched part removed. It has 2 switches for AC. Normal and Max AC. Changed Speed sense controller for blower Motor, part matched removed part. I checked system after each part. Dash control panel, no change. No fan, no control of fan. Changed speed sense controller on air box. Fan came on high for 2-3 seconds then speed dropped very slightly. AC Clutch no longer engages now. Changed blower motor, no change. I double checked fuse 15 passenger side foot panel, good. I checked fuse 45 same panel, good. I swapped relays with know good relays numbers 3, 23, 43, and 51. I may be wrong about the numbers 23, 33 because of memory but 3 and 51 are right for sure. The other ones were all for blower motor, AC, HVAC, AC Clutch etc. Anything that had to do with AC, blower, clutch HVAC etc I swapped. I crawled under truck saw no worries broken at AC compressor and connections were tight. Not easy with my disability. lol. That's where I'm stuck for now. I could take to a dealer but I'd get raped and I'm living in just disability. I've been walking my wife through what I can't get to and she's been doing great so far. My knowledge, her hands. I really appreciate you taking time to try and assist me. Super Appreciate it.

 

OK the AC compressor is grounded on one side and gets it's power from the AC Clutch relay which is part of the BJB (Battery Junction Box). the relay gets it's power from fuse F30 on the same box. The relay's ground is controlled by the PCM (Power Train Control Module) pin 2. The relay coil gets it's power from fuse F77 on the BJB. But that fuse gets it's power via the PCM Power relay on the BJB. So check and be sure that you have power at F77. The PCM relay gets it's power from fuse F34 on the BJB, it should be hot at all times. The PCM Power relay is controlled via it's ground from the PCM pin 38. The other side of the coil should be hot at all times. After that it looks like everything on the PCM is controlled MCN (Module Control Network).

There is an AC Pressure Transducer that connects to the PCM also. Pins 58, 31 and 52 of the PCM connect to pins 1, 3 and 2 of the transducer. It looks like that is a poteniometer and that pin 31 is the wiper. The signals are labeled Sigrtn, ACPT and Vref respectively. So signal return, probably a go/no go signal and a voltage reference.

There are four temp sensors in the system that I see. The Autolamp/Sunload sensor (two different signals to pins to 19 and 18 on the HVAC module), the Evaporator Temp sensor to pin 19 (that conflicts with the Sunload sensor pin number!), Ambient air temp sensor to pin 15, and the in-vehicle Temp sensor to pin 8 of the HVAC module. Th other side of all of them connects to the HVAC Return line (pin 23) on the other side. The Sunload sensor also has a connection to the SJB pin 46.

The Sunload sensor appears to be two photocells based on the schematic. The others appear to be variable resistors. NTC thermistors I would guess.