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I recently changed the oil pressure sensor and must have broken a wire in the harness because the gauges were all dead and wait to start light was flashing when i got done. The local diesel mechanic decided it was a broken ground wire in the harness and instead of tearing the harness apart, just added a ground wire to the tps sensor plug. Its a manual truck so it doesnt have a tps. Everything was back to normal and worked great. A few days later the ac quit cooling completely, like i flipped a switch. I saw that it had a blown fuse so i replaced and swapped relays and it popped as soon as I turned the ac on. I unplugged the compressor from the harness, put in another fuse and it popped as soon as i turned on the ac again. The reason I took it to a mechanic is because im horrible with wiring and the wiring diagrams look like and alien language to me. Anyone got any help for a dummy?

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36 minutes ago, 98whitelightnin said:

I saw that it had a blown fuse so i replaced

Was it the fuse in the PDC, 10amp, at the J position or the #11 fuse, also 10 amp, in the junction block (left side of dash)?  

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There maybe a direct short to ground in the dark blue/black wire from connector C125 to the AC compressor.   Unplug the wire at the compressor and the c125 connector, located next to the vacuum T fittings at the fire wall,  and ohm test it.  If the reading is 0 or close to it there is a short to ground in that wire.   If that's the case then you will have to find where it is and repair it or cut the wire about 3" from the engine side of the C125 connector and run a new 18 AGW to the connector at the AC compressor.

If ohm reading is L or 1000 then ohm test the wire between C125 and pin 87 of the relay plug. 

 

.1989358549_ACcomp.jpg.ab5fe3fb71e4590cb18c301956ca7a7a.jpg  

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The c125 above the fuel filter housing?
 

Ohm testing the black and blue wire at the compressor. Does it go into 87 in the c125? 87 looks to be red/blue tracer

Ohm testing between blue/black wire at the wire that plugs to the compressor and 87 of the c125 is starts out high and then goes down to 00.9

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40 minutes ago, 98whitelightnin said:

The c125 above the fuel filter housing?

Yes, there are two connectors above the fuel filter housing at the firewall.  The db/bk wire is in the one with 11 wires in it at pin #4. 

You need to disconnect the wire harness at C125  then do the ohm testing.  This will isolate just the wire in the engine harness and you can see if this is the one shorted to ground.

To test the wire from C125 to terminal #87:  with  C125 still disconnected remove AC relay from PDC, find terminal #87 position and with one probe from the ohm meter touching the terminal and the other touching ground the reading should be L or infinity depending on the meter.

 

Now do the same with the C125 connector still separated at the wire unplugged from the AC compressor and ground.  The ohm reading should be the same as above.  If in either test the ohm reading is near or at 0 then there is a short in that wire.

 

 

 

1957040355_Scan_20180624(11).jpg.16f8e6471d03398ee1d6df06dfc701a2.jpg 

2141433412_Scan_20180624(4).jpg.f0e145aee0cd2fdae45f9041c6567d10.jpg

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I noticed at the plug that goes into the ac compressor, the black/blue wire is exposed right at the plug. I put it all back together and just for fun put a fuse in and it’s working again. Went for a 30 minute drive and it never missed a beat. I’m sure it will wait till I’m on a road trip to ground out again.

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