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Discussion Starter #1
Hi everyone, I'm looking for some help or insight from people out there that may have experienced this before. All my diagnostics keep pointing at the pcm.

My problem is when you turn the ac on in the cab the compressor isn't engaging. I started with all the simple things like fuses and relays. And checked to make sure I have the correct 1.1kg charge in it. I even printed the wiring schematics for the 6.0 engine harness and the entire ac system. I have power everywhere I'm supposed to according to the schematic but it seems as though the pcm output to the relay isn't working. I can even jump the relay with my power probe and it will engage the clutch. If I jump it at the high pressure switch it engages. I jump it on the pcm input at the high pressure switch it engages. I hook up our scanner at work and look at the pids for ac and its saying "ac not requested by driver" when the switch is on. So I'm kinda lost and getting frustrated.

A little about the truck.
April of 03 6.0 5r110 f450
Now using a 05 cummins and 13 68rfe auto
Ac wiring is 100% original ford minus the compressor pigtail
New compressor, condenser, accumulator, high pressure switch, clutch cycling switch and hoses all when the cummins was installed.
172k on the chassis. 117k on the motor. 1300 miles since the swap.
 

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Native Texan
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9,033 Posts
Hi everyone, I'm looking for some help or insight from people out there that may have experienced this before. All my diagnostics keep pointing at the pcm.

My problem is when you turn the ac on in the cab the compressor isn't engaging. I started with all the simple things like fuses and relays. And checked to make sure I have the correct 1.1kg charge in it. I even printed the wiring schematics for the 6.0 engine harness and the entire ac system. I have power everywhere I'm supposed to according to the schematic but it seems as though the pcm output to the relay isn't working. I can even jump the relay with my power probe and it will engage the clutch. If I jump it at the high pressure switch it engages. I jump it on the pcm input at the high pressure switch it engages. I hook up our scanner at work and look at the pids for ac and its saying "ac not requested by driver" when the switch is on. So I'm kinda lost and getting frustrated.

A little about the truck.
April of 03 6.0 5r110 f450
Now using a 05 cummins and 13 68rfe auto
Ac wiring is 100% original ford minus the compressor pigtail
New compressor, condenser, accumulator, high pressure switch, clutch cycling switch and hoses all when the cummins was installed.
172k on the chassis. 117k on the motor. 1300 miles since the swap.
I have seen this before on these 6.0l. If you can jumper the switch then its a bad switch. the switches tell the pcm hey he wants ac and the system is good to provide it. If it was the pcm then jumping the switch would do nothing.Which switch are u jumping the duel pressure switch in the lines or the cycling switch on the accumulator. The cycling switch is a common failure. If u are jumping from one side to the other then bad switch if u are providing power to the wire. then check the violet wire from the control head. I had one go bad and ran a new one from the head to the cycling switch. Its not the pcm its not turning the ac on cause as far as it know its not wanted. because of a failure in the request line.

Give it to Mikey. He won't eat it he hates everything. Hey Mikey!! He Likes It.
 

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Discussion Starter #3
I can bypass the switch at the accumulator and it does nothing even though I have 12v on the violet. I move down to the dual pressure switch and I have 12v also. If I apply power to either tan and lt.green it will kick on the compressor. Both switches are new. I've evacuated and recharged the system 3 or 4 times now. I've put the 1.1kg in and it makes about 85psi on both gauges. I've tried to lower the charge down to about .5kg just to see if maybe it was overcharged. Still nothing. I even replaced the ac clutch relay to no end.
 

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Native Texan
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If u have 12v on the red/yellow wire u should have 12v on one of the tan/lt green wires. the blk/yellow should have ground and the other wire should be grounded. just cause u replaced the switch does not mean its good.

Give it to Mikey. He won't eat it he hates everything. Hey Mikey!! He Likes It.
 

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Discussion Starter #5
True about the new switch being possibly bad. That's the point behind bypassing it with a jumper wire. I haven't tried jumping both at the same time yet though.
 

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Discussion Starter #6
Since there are 2 tan/lt.green wires does it matter which is jumped to the red/yellow? I'll probably try that next. The more I think about it, the more it seems to be loosing the signal at the dual pressure switch.
 

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Native Texan
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Pin 1 is red\yellow
Pin 2 is Blk\yellow
Pin 3 is Tan\lt green for pin 2
Pin 4 is Tan\lt green for pin 1
 

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Discussion Starter #8
Right. I was reading that when I got home a little while ago. My diagram says 1&4 go together and 2&3. So I'd need to jump red #1 to tan #4? Maybe I'll mess with it if it ever stops raining this weekend.
 
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