ac wireing and the dreded PCM

Cummins Conversion & Builds

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ac wireing and the dreded PCM

Postby jethro » Mon Sep 12, 2016 8:52 pm

2004 f-350 with first gen 6bt.
Just got the air conditioning plumbing fabed and installed, got it gasses up and it cools fine. I just hot wired the compressor clutch while charging it up. (using first gen compressor that was on engine---- 42+1/2 oz 134a and 9 oz pag 45 gave me
28 lbs and 210 lbs at idle-- about 75 F ambient. )

Now - the REAL problem is that the previous owner cut off the ends of the engine harness. To compound the problem some more----- I have the PCM schematic ---- but not an accurate wiring diagram which shows the wire colors ----- apparently
Ford doesn't want you to have one of those. I have the Haynes book - but it is for 2001- which is different.

Basically there are 2 circuits involved. First circuit.....Hot wire starts at dash ac control--- goes through primary side of ac relay-- through a normally closed high pressure switch-- then to the PCM. (going from memory here)
Second circuit--- low pressure switch (normally open) hooks to PCM on one end and grounded on other.
Well- sorry- third circuit-- power from Batt junction box flows through secondary side of relay and then on to compressor
clutch coil.

I believe I have 2 parts wired--- but the wires for the low pressure cycling switch go into the big fat harness bundle on the passenger side and go across (apparently) to the drivers side near the PCM------ but I cant find them.... they are none of the cut wires, they are not showing continuity with ANY of the PCM pins.... I can see them on the PCM diagram-- but that does not
show wire colors.... the Haynes book if for 2001 and they don't have for 2004- which is obviously different.

I have hooked my meter to the switch wires on one end and touched every wire I can get to-- open ones and all the PCM pins.
One side of the switch shows (PCM Diagram)to be grounded.... but neither side of the plug tests common with ground. (?)
yet both wires go into the main harness trunk. as the saying goes ---- WTF

anyone have any ideas ?

Tim
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Re: ac wireing and the dreded PCM

Postby DodgeFreak » Mon Sep 12, 2016 10:23 pm

Hope this helps. If you need me to I can email you the pdf. I had to take a picture of the printed version because when I scanned and emailed it to me it sent it as a pdf again. Lol
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92 D350 Cab and Chassis. Auto stock, wiring gremlins. 330k miles
92 W250 Ext cab rotted completely out. Auto, pump maxed, 215 ppump nozzles, Denny T2 pin.
85 D350 single wheel, converted to cummins, getrag, turned up 2 turns and afc screw flush.
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Re: ac wireing and the dreded PCM

Postby jethro » Tue Sep 13, 2016 8:41 pm

Thank You DF ------
I talked to shaun at Diesel Conversions---- he didn't know from memory where the ends of the wires come out. He pointed out that
the PCM wont enable the AC until it sees a Tach signal into the PCM.
I am considering just wiring the AC circuits outside the PCM's influence. May just add a relay on the passenger fender and go from there.
I will examine you diagram tomorrow (having tropical storm tonight) and see if it sheds light on the problem. Perhaps I can find the wires yet !

Thank you for the help.....
Tim
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fuel screw!!!!
 
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Re: ac wireing and the dreded PCM

Postby Gots_a_sol » Thu Oct 06, 2016 1:38 pm

I wrote down how to make the AC work by bypassing the PCM in my thread here viewtopic.php?p=162830#p162830


That should give you an idea what needs to be done, wire colors/pin locations may be different.
-Joe

00 Excursion - 12v/nv4500, he351cw, 5x12s, 366 spring, THD piston pump, 4" intake/exhaust
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