AC clutch does not engage
 

2006 Ford F150 Lariat
All controls work on the dash. Blower motor runs fine, ac indicator says it is on but no power to clutch. I have no power at ac pressure cut off switch. I can though put 12 volts to one side of the pressure switch and the clutch engages. Where does the power signal for the clutch to engage originate? Again all controls on dash are the same as always. I have checked all known fuses and change them just to make sure. Does anyone have any ideas? Thanks

Do you have manual climate control or automatic climate control?
I assume that when you move the temp dial the cabin temp follows it, is this correct?
You said that you put 12V to one side of the pressure switch, can you specify which pressure switch this is?
The HVAC module sends voltage through both the AC high pressure switch and the AC clutch cycling pressure switch to the PCM, if the PCM determines is ok to turn on the compressor clutch on it grounds the AC clutch relay.

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Swap the relay with a good one. See if it works. Most likely bad psi switch or compressor clutch. Psi switch is cheaper to replace if it is bad. Ur age. Compressor ! Most likely

Its not a relay since he can apply 12V to a pressure switch and the clutch engages. As such it has to do with the control side.

Then replace the Heater/AC control unit in the dash for the AC heater Control It is a component and is replaced as a complete one for the particular model of truck. No power to the switch with a good relay means the processor board is cooked in the dash !

https://oemusedautoparts1.com/produc...a122df53086809

We do not know which switch @racingsinger supplied 12V to, high pressure switch or clutch cycling pressure switch. If it was the clutch cycling pressure switch then the high pressure switch could still be at fault. Or the wire could be damaged between the HVAC control and the high pressure switch.

@P_T_ Would you let a shop charge you to throw the parts your listing and hope it works without checking anything else, cause thats what your doing.

Should be around 5.5 volts from car AC puter in heater control to activate pressure switch. Not there then fuse is bad or puter is bad. Disconnect switch and test for voltage if there just jump plug and compressor clutch should engage. No engagement bad clutch ! U need this to trouble shoot.

https://www.ebay.com/itm/All-Sun-EM2...53.m2749.l2649

https://www.ebay.com/itm/All-Sun-EM2...72.m2749.l2649 U need this to safely trouble shoot a Vehicle electrical power systems (aka) with unplugs and pulled relays.