2nd Gen Non-Engine/Transmission Power Distribution Center

[Jeff L]

Troubleshooting a non-operative AC system lead me to the power distribution center. My intention was to check the relay, but there's no need for that. There's no voltage to the relay. There is also no voltage to the horn's relay. In addition, initially the flasher's circuit was dead, but after a jiggle 'n' wiggle session with the switch on the steering column, that circuit is operating.

What am I up against?

thanx in advance,

Jeff

 

[PBJ2500CTD]

Jeff,

First order is to identify your vehicle. This wil help those with the specific information to come to your assistance.
If I were to use my 2002 book I would suggest that you check two fuses in the PDC; one for AC and one for the horn.
Also, additional information on the AC issue. Is your heater fan running in all four positions? Does the AC compressor cycle? I would assume not since you have no power to the relay.

There is a starting point...

 

[Jeff L]

Yeah, I kinda forgot the cart (not just put the horse in front of it). The vehicle is a '96 Ram 2500, 4x4.

Fan works fine (blows hot air, January-through-December) - grins

Just ordered a factory service manual, as the aftermarket manual I'm using isn't the answer.

Near as I can tell, I'll be learnin' 'bout contraptions with acronyms like: IPM, PCM, ECM, and PTC (these provided via the search function, right here on TDR, hey, another acronym). And all I wanted was a little cold air!

 

[PBJ2500CTD]

Jeff,

Since you have an operating heater/AC fan I would check the charge in the system. It could possibly be a system in a state of low/no pressure, or switch/connector issue in one of them-there acronyms y'all mentioned.

 

[JMcCoy]

Can you hear/see the compressor clutch cycling in and off? If it is cycling every few seconds, it is low on R134a. If it is not cycling at all, check the electrical connection that plugs into the compressor. I would work backwards from there. If there is a leak in your system, 9 times out of 10, it will be your evaporator. I went through three in just a few years (just out of warrantee of course), until I got the updated Mopar unit over 10 years ago. If that is the case, I believe Geno's sells them now. Good luck and please keep us posted.

 

[fest3er]

There is a possibility that your PCM no longer signals that it's OK to run the compressor. My '98 did this years ago; the shop ran a wire from the PDC to the low pressure switch and completely bypassed the PCM. I've never had a problem with it since. The PCM cuts off the compressor during full throttle, as though the Cummins is a wheezing, asthmatic gasser that couldn't make it over a small foothill without full throttle and downshifting a gear or two. Obviously, this feature isn't needed.

If the system pressures are OK:

• Momentarily jumper B+ to the clutch side of the high pressure switch; the A/C clutch should engage. (Not too long; if the compressor opens its relief valve, you may soil your trousers.)
• Momentarily jumper B+ to the clutch side of the low pressure switch; the clutch should engage (and the high pressure switch will be safely active).
• Momentarily jumper B+ to the other side of the low pressure switch; the clutch should engage (and the low pressure switch will be active).

This will tell you if the high pressure switch, the low pressure switch, or the PCM is preventing the compressor from running. My bet is the PCM, though the low pressure switch is a close second.

Thinking it differently, you should see B+ all the way to the clutch. If you don't, where it gets lost will tell you which component is bad.

 

[Jeff L]

'Poligize for the delayed response (business trip ya know).

All responses have been read, and are 'preciated. Hope to get back "at it" in a day or two.

Still ponderin' why there is no power at the relay however. Seems to me that position 30(?) on that relay should have B+ at all times.

 

[Jeff L]

Turns out the Horn's circuit in the Power Distribution Center provides B+ for the A/C circuit. Nothing (to include the factory service manual) indicates that nice bit of info.

Cavity #30 for the compressor relay should indeed have B+ at all times, and if it doesn't, check the 20 amp fuse labeled "Horn".

Long story short, the coil for the compressor clutch was shorted, which of course blew the Horn's fuse. Yeah, that's just how I thought it would go........

 

[CharlieFoxtrot]

Glad you found it!

Your list of acronyms above included PCM. That's for those guys with newfangled motors with twice as many valves as needed. We don't have those. Or lots of other crap with wires attached.

 

[Jeff L]

Thanks!

Hate to tell ya though, my PCM is on the firewall, right next to the A/C accumulator - and it has lots of wires attached to it (though only half as many as a gasser, and a quarter of those of a newer diesel). I have a tough enough time with this comparatively simplistic vehicle. Don't think I'd spend much time under the hood of a newer one.

***fuse blows, but the horn won't.............horn blows, but the fuse didn't...........fuse didn't blow, horn will blow, still no A/C.......*****

^^^^^^^random musings ^^^^^^^^^

 

[CharlieFoxtrot]

Well that's disappointing! I thought I had avoided all that computer crap, besides whatever handles OD & lockup on the automatic. So we still have a computer that messes with the alternator and AC and whatever else it does...

Sorry for the misinformation...

 

[cerberusiam]

That's for those guys with newfangled motors with twice as many valves as needed. We don't have those.

Oh, yes they do. Late 96 has a PCM for all the trans and other controls. Early 96 still had what was called and SBEC but it still controlled a lot of things like charging, grid heaters, etc.