hey guys. i posted this in the main dodge forum, then realized that there's a diesel forum so i wanted to post this here since you guys might have some more experienced insight ...

i've got a new-to-me '94 ram 3500 turbo diesel. the a/c and horn don't work, and after troubleshooting today i realized that the horn works fine until you try to turn on the a/c, then the horn fuse blows. so i disconnected the compressor and tried again, cranked the air on and hit the horn and the fuse had not blown. there's obviously a short somewhere. i figured something was up with the compressor in the first place because i've never seen the clutch kick on, even after shorting the clutch cycling switch and testing the system pressure (which is good). i pulled the two-post power connector at the compressor and tested the voltage, i'm getting 14 volts there so that looks alright. i then got a continuity tester and hit the two posts on the compressor side of the wiring harness and got a long beep, which means that those two wires going down into the compressor are shorted out somewhere. a visual inspection didn't show where any wires had rubbed through the insulators (which is what i expected to find) so the problem has got to be the compressor itself.

can anyone back me up on my opinion, or was there something else i can check? providing it is the compressor, anyone know what the damage is going to be to have a new one put in?

thanks in advance!

 

measure the wires going into the compressor to the compressor housing (looking for a short to ground). On most of the semi's they use a compressor with a servicable clutch meaning you can pull the clutch off the front of the compressor and replace it. However I'm not sure if dc uses servicable clutches.

 

thanks for the tip. i already measured at the wires going into the compressor housing and it's definitely shorting out, however i think it's got to be inside the compressor housing since the wires look good all the way from the harness to the compressor. there are no nicks or rubs through the insulation into the wires where it could be shorting. i'm not sure about the servicable clutch. there are a series of 6 or 8 bolts that are between the pulley and the main compressor housing that make it look as if the clutch and pulley would come off pretty easily. if that's the case, would the system need to be evacuated before removing the clutch? thanks!

 

You don't need to recover the system if it is a removable clutch. Those bolt you speak of are not to remove the clutch. Those open up the crankcase of the compressor. There should be one nut on the end of the shaft, then the outer friction surface comes off, then some snap rings then the pulley comes off, then another snap ring then the coil comes off.

 

that makes sense, thanks. here's what doesn't make sense and i'm hoping someone can help me with this part. so i went and picked up a new compressor. the new one did not come with a wire harness installed, it just has two red wires coming out of the housing with nothing to differentiate positive from negative. while trying to determine this using my multimeter i discovered that, just like my old compressor, the wires coming out of the housing indicate a dead short between the two when checked with the continuity setting on my multimeter. what am i missing here? are both leads supposed to be hot and it grounds internally via the compressor chassis? that's the only thing that would make sense to me, but that wouldn't explain why the wiring harness on the truck side (as opposed to the compressor side) has a striped wire that typically indicates negative. so my questions are:

1. is this normal?
2. does it matter which way the wires are hooked. if so, how do i tell them apart?

thanks in advance for any info.

 

What does the ohms meter read? It is normal to have some resistancein the coil. Itwill notmake a difference howthe wires are hooked up in a simple coil. I would check for a poor ground somewhere... Sounds like the pull up is to high due to too much resistance in the circuit, blowing the fuse. Usually caused by loose or corroded ground. This also would explain the clutch never coming on. If you put you meter on the clutch wires while hooked to the clutch, what are the volts then? If the voltage goes low, then try putting the ground lead directly to battery ground, if it goes stays around 12 VDC then the ground is the problem.

 

thanks, makes sense. things look good now. i installed the new compressor, vac'd the system down to -30 and left it overnight just to see if there were any slow leaks that would show up. this morning the system was still holding the negative pressure so i charged it up and it's blowing nice and cold. woohooo! this time of year in texas, a nice cold a/c is a must have.