Troubleshooting AC electrical problems

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Aug 23, 2015 | 09:17 AM

rshiver

Thread Starter

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Joined: Dec 2009

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Troubleshooting AC electrical problems

Hey everyone, I have a 96 F-150 4.9. AC compressor will not engage. I have checked for power thru the low pressure and the hi pressure switch, everything is good. The only place I don't have power is at the compressor. I looked at a wiring diagram and it appears the power routes back through the PCM. My question I guess is does the PCM control the power to the compressor?

Many Thanks...

Aug 23, 2015 | 12:02 PM

F350 1990

Fleet Mechanic

Joined: Feb 2007

Posts: 1,652

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From: Mooresville, NC

Your next checks if there is no voltage at the compressor

Wiring & fuses
A/C clutch resistor diode
EEC

Aug 23, 2015 | 02:21 PM

rla2005

Fleet Owner

Joined: Oct 2005

Posts: 20,789

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From: Kentucky

Quote:

Originally Posted by rshiver

My question I guess is does the PCM control the power to the compressor?

Many Thanks...

No, the PCM does not turn the AC compressor On/Off. That tie in is the signal telling the PCM the compressor is engaged. In theory the PCM uses that to calculate engine load.