2nd Gen Non-Engine/Transmission No AC!!! HELP!!!

[BCFAST]

Was working just fine. . then came the warm air thru the vents. The blower works OK, but the compressor wont engage. I looked thru the relay boxes, did some swapping and it still wont engage. What am I not trying>? Is the rotary dash switch a possible culprit? Its darned hot and any help is greatly appreciated!

 

[Cooker]

You may have a leak



If the refigerant is too low the compressor won't engage.



-Ryan

 

[MCummings]

Check out the fuses inside the cab.



Does your overhaed temperature and compass work?

Mine did the same thing, and it happened to be the "ignition o. d. fuse was not getting good contact.



Could be a cause.



MerrickNJr

 

[BCFAST]

Thanks guys. My overhead is working. I didnt see any burnt fuses in the box. The way it just stopped working suddenly leads me to believe it's an electrical issue... but I cant seem to find anything so far... . keep those ideas comming!!!

 

[fest3er]

Originally posted by BCFAST

Was working just fine. . then came the warm air thru the vents. The blower works OK, but the compressor wont engage. I looked thru the relay boxes, did some swapping and it still wont engage. What am I not trying>? Is the rotary dash switch a possible culprit? Its darned hot and any help is greatly appreciated!

Yup. Just like mine recently. It worked. Then it didn't. Everything checked out, except that the compressor wouldn't turn on. The man at the shop suggested bypassing the PCM and let the A/C control actually control the compressor. Since there were no drawbacks, I sure, "Sure!". He did, and the A/C works flawlessly now. FOr that matter, with the work he did, it actually works better than ever!



<<Technical details>>

When you turn on your A/C, you are actually asking the PCM to activate the compressor. If something is wrong with the PCM or its wiring, it may just fail to engage the clutch relay, as happened on my truck. Since the Cummins has more than enough torque and HP to haul us up hills, we really don't need the PCM disengaging the A/C upon full throttle. (Last time I checked whilst careering up a 7% grade, I think I gained all of 1MPH when I turned off the A/C, if even that much. ) I believe that's the only reason the A/C control is routed through the PCM. If I'm wrong, let me know; I'm a man and can take it!



Fest3er

 

[Deezul1]

When my 96 did that it turned out that the compressor clutch connector underneath and worked loose, pushed it together and it worked great.



fest3er

How did your mechanic bypass the PCM, I have wanted to do that for everything, DONT NEED NO STINKIN PCM

 

[BCFAST]

PCM??

Sorry guys... . I do race cars with carburators or mechanical injection... . I dont know much about computerized stuff. What's a PCM, and where is it in the truck? At this point, I'll pretty much try anything! Dang, it's hot!

 

[Deezul1]

The PCM is the ^&$%&^computer that controls the AC and cruise control and thats about all on a 12 valve. As far as I know its only function is to make it hard to work on those 2 units, they certainly dont need a puter to function, might have something to do with the auto trans dont know about that.

 

[fest3er]

Originally posted by Deezul 1

The PCM is the ^&$%&^computer that controls the AC and cruise control and thats about all on a 12 valve. ...

There's more to it than that. The PCM controls the dash display. It stores the total elapsed miles and will reload the dash display as needed. It tells the odo what miles to display. It tells the speedo what to display. It operates the cruise control. It operates the intake heaters. It controls the TC lockup. It controls the transmission (auto). It tells the dash what RPM to display. It controls OD (auto). It tells the dash what fuel level to display. It controls A/C compressor operation (on/off, I think). It controls the fuel shutoff relay(s). It contains the voltage regulator. It tells the dash what oil pressure to display, what coolant temp to display. It disengages OD if the transmission is too hot. Or too cold. It monitors intake air temperature. It monitors the water-in-fuel sensor.



It *does* serve a useful function. Your truck might not run too well if you simply removed it; you would certainly have no dash gauges working without the PCM.



As to removing the PCM from the A/C circuit, I believe the mechanic ran a wire from the A/C relay in the PDC under the hood to the A/C 'request' line from the dash A/C control, and disconnected the two respective wires running to/from the PCM.



On my '98, that would appear to be pins 1 and 22 on the PCM connector C3. Pin one is the A/C relay control, and pin 22 is the A/C switch sense. Clip these two wires and tie the wire-ends together. Then thoroughly insulate the connector ends from each other and from any ground. (Fold 'em back an inch and tightly wrap electrical tape around each one. Then put a small cable tie on each to keep the tape from coming loose. Be sure to completely wrap the 'loop' in tape, to keep moisture out. )



I'm not 100% certain of this procedure. I would have to visit the shop and ask. You mustn't simply jumper to the A/C clutch itself; you need the high-pressure and low-pressure switches in place so the system can 'regulate' itself.



To test to see if your A/C compressor is working at all, you could pull the A/C relay in the PDC under the hood, and run a jumper from 'cavity 30' to 'cavity 87' on that relay position. 30 contains B+ voltage, and 87 is the wire going to the compressor.



This is all in the service manual. It takes some spelunking, but the info can be found in section 8W. *I* wouldn't do it without having the SM handy. The diagrams are quite useful in figuring out what pin is what. If you don't have an SM, visit your nearby friendly Dodge dealer and ask to peruse his. They might even make copies of the relevant info for a nominal fee.



I had the shop bypass my PCM because, at 95K miles, I'm near the end of the engine warranty. Besides, I never relied on the warranty anyway. When Dodge covered something, I was pleasantly surprised. When they didn't I paid what I expected to pay in the first place.



Fest3er

 

[work2muchplay2little]

I'll second the motion that Cooker made. The most common reason for A/C to quit working is low refrigerant level that will trip the low pressure switch on the receiver/dryer and cut out the compressor clutch to prevent the compressor from grenading due to a lack of circulating oil. I'd get the pressure on the system checked and refilled if necessary.

 

[DieselDoghouse]

Its Deja Vu time!!! Just been there. Pull the connector on the low pressure switch located on the accumulator (the small tank by the firewall) and short the contacts on the connector (this mimics a healthy charge), any action?? If so your electrics should be ok but this switch is bad (it thinks the charge is low) or your charge really is low. Then you need a manifold (a frame with a low pressure gauge and a high gauge) to plug into the appropriate shraeder valves to test the charge - best to get some help familiar too. Even if your low pressure side is low, if it drops (high side should try to rise) when the compressor comes on the compressor is probable ok. With a HVAC friend I found my charge was down, but we never found a leak. One odd thing, my AC has ALWAYS cycled ~8 times per minute at least since new. Now with a proper charge IT DOESN"T CYCLE AT ALL at 80 degrees and I could store snow cones for Satan inside!! I had once heard a rumor that these systems weren't always getting charged right on the assembly line. With even normal losses over the years some of us may then be hitting the point where the low switch disallows AC legitimately.

 

[EB]

I know you said you cked the fuses, but does your horn work? On my 95 3500 my ac compressor quit and i found that the horn was shorted and it blew the fuse under the hood. I believe it was a 20 amp fuse. Maybe will help. EB

 

[Deezul1]

fest3er



Thanks for that info, I didnt realize the puter was so deep into all those areas and its good to know. I wasnt advocating its removal as I wasnt sure what it would take to make everything work without it, I was thinking more along the lines of the puter performs no useful function on a 12 valve truck as I have had many vehicles that had all the mentioned devices and they worked great without a puter and were way easier to trouble shoot. With all the electronics on the 24 valave its a must but not so on a 12 valve, just a PITA.

 

[HFreeman]

fest3er



Thanks for that info, I didnt realize the puter was so deep into all those areas and its good to know. I wasnt advocating its removal as I wasnt sure what it would take to make everything work without it, I was thinking more along the lines of the puter performs no useful function on a 12 valve truck as I have had many vehicles that had all the mentioned devices and they worked great without a puter and were way easier to trouble shoot. With all the electronics on the 24 valave its a must but not so on a 12 valve, just a PITA.

Deezul1... ... ..... I have a '95 3500 auto and the other day I somehow cooked my ASD + who knows what else. I lost O/D control, speedo, tach, manifold heater guage, ummm... A/C compressor, and some other stuff. I saw a thread yesterday ( I forgot what it was ( dumb, eh? ) and there was something about an engine speed control as well as a PCM problem. BTW, no generator charge and I have to wire the ASD open to start and close it (under the hood ) to shut engine off.

As far as the truck running OK, It runs fine if you don't care about overdrive, ( auto ) , speedo, tach etc. I hope this provides some clarity as to the importanse of the bloody PCM. Har Har. Good luck to both of us.

 

[SBillinson]

Bad Compressor?

My AC stopped working a couple of months ago and I suspected it was the compressor. The clutch will engage for a second then stop, then re-engage, then stop. No cold air.



Bad compressor? Or could it be the same wiring issue described here? Would be great to know before I go out and spend $400. Thanks



Steve

 

[HFreeman]

Was working just fine. . then came the warm air thru the vents. The blower works OK, but the compressor wont engage. I looked thru the relay boxes, did some swapping and it still wont engage. What am I not trying>? Is the rotary dash switch a possible culprit? Its darned hot and any help is greatly appreciated!

Steve. . in the past when that has happened to me the cause was loss of vacuum in the

system. Also low or no freon will do the same thing. The compressor will turn on for a bit, then quit

There should be a 'low freon' switch somewhere in the circuit. Haven't looked at mine yet.



I hope this helps.



Hank