So the A/C doesn't work on my 2006 F150 with the 5.4 engine. I was able to download the wiring diagrams and have verified that when jumping the A/C clutch relay the A/c does engage and it does cool down the truck. I also verified that the PCM is receiving a 12V signal from the dash A/C switch so I know it's not a pressure issue or the dash switch. I have also checked all related fuses and no problem found. I also checked the signal wire from the PCM to the A/C clutch relay, no problem there. It appears as though the PCM is not switching in the ground to the clutch relay. Does anyone know if there's any other signals the PCM requires to engage the A/C clutch relay? I also checked the grounds going into the PCM in the same plug as the A/C controls and they were all good, I assuming one of those grounds is what the PCM is using to switch the A/C clutch relay on?

Thanks in advance for any suggestions.

 

Have you tried jumping the pressure control switch(es)?

 

Yes, I jumped both pressure switches and I get voltage from the dash A/C switch through the pressure switches to the PCM. For some reason the PCM is not applying ground to the A/C clutch relay.

 

Have you scanned the PCM ? It will automatically disable the A/C if there are certain faults present.

 

Sree if this helps. It's from a 2004 F150 Workshop Manual:

The A/C compressor clutch will only be engaged by the PCM if all of the following conditions are met:

• The climate control assembly is set to a mode which provides an A/C request to the instrument cluster. this request is then transferred to the PCM through the CAN bus.
• The A/C cycling switch is reading an acceptable low side refrigerant pressure.
• The A/C high pressure cutoff switch is not open due to excessive pressure in the high side of the refrigerant system.
• The A/C compressor relay is energized by the PCM.
• The engine coolant temperature is not excessively high.
• The PCM has not detected a wide open throttle (WOT) condition.

As previously mentioned, checking for trouble codes may provide a clue.

 

Thanks for all the suggestions, I did check for codes when this all started, there were none. I’m wondering if the climate control module is not communicating with the PCM through the can-bus. I am not sure how I’d check that.

 

Could this be why the PCM isn't grounding the clutch relay?

Air Conditioning (A/C) Cycling Switch

• The A/C cycling switch is mounted on a Schrader valve-type fitting on the suction accumulator.
• A valve depressor, located inside the threaded end of the A/C cycling switch, presses in on the Schrader valve stem.
• This allows the suction pressure to control the operation of the A/C cycling switch.
• The electrical switch contacts open when the suction pressure drops.
• The contacts close when the suction pressure rises.
• When the A/C cycling switch contacts close, the signal to energize the A/C compressor clutch field coil is sent to the PCM.
• When the A/C cycling switch contacts open, the A/C compressor clutch field coil is de-energized and A/C compressor operation stops via the PCM and A/C clutch relay.
• The A/C cycling switch will control the evaporator core pressure at a point where the plate/fin surface temperature will be maintained slightly above freezing.
• This prevents icing of the evaporator core and blockage of airflow. It is not necessary to discharge the refrigerant system to remove the A/C cycling switch.