I just purchased a 91 d 250 reg cab with 200,000miles on it.
So far I have redone the brakes, and fixed the power windows.
I have now moved on to the AC.
I was unsure exactly what condition the system was in so i put on r-134 fittings, and replaced the expansion valve and the drier accumulator. I now can hold vacume!
I cannot get the compressor to engage, even after shorting the sensor on the expansion valve.
I have a few other problems that might or might not be related.
the cruise controll doesnt work at all, and the radio doesn't come on.
and the starter uses an external switch to engage.
all the fuses are good.
I have heard some people talk about the computer on these things taking out the AC and cruise.
Is there a way to check the compressor without taking it out?
How do I trouble shoot the cruise controll?

 

When I bought my 92 W250 last year it had electrical problems, the A/C didn't work at all, and when the underhood temp. reached a certain point POW the SBEC took a crap. I would instantly lose the cruise control and the charge gauge would drop (lost alternator field). Then the wait to start and water in fuel lamps would start to come off and on while driving down the highway (psyco). My truck only ran through the faisco because it is a stick, if it were an automatic the engine start solenoid would have shut down with the alternator field.

My A/C immediately worked for the first time with the reman SBEC, all other problems went away. That was 25,000 miles ago. NAPA had them for a fair price.

Dodge had plenty of other problems with ignition switches and the coil for the cruise control on the steering wheel. Get a wiring diagram and chase down your problem.

 

whats the SBEC, what year did they start with them, would a 91.5 have 1

 

I have a 1991 D-350 and when my A/C died, the compressor would not engage. There is no computer on a 91 at least that controls the A/C.
If you short out the low pressure cutout on the side of the H block and the compressor will not engage then the next probable fault will be the relay that is located inside the compressor cycling switch. It is the box that is mounted to the side of the H block and has the probe that is inserted into the suction tube.
They are somewhere around $100.00 from Dodge. I removed it completely and used the ground trigger to the cycling switch to energize a Bosch relay, which directly controlled the compressor coil. I originally made this modification in a parking lot to get my AC working while on a road trip. I then refined it when I got home.
The only minor tradeoff is occasional evapaporator icing but I put a toggle in the trigger circuit and I can control the cycling. Plus I can recirculate the inside air with the cold turned off.
I think that is where your problem will be.
Jim

 

thanks for the advice.
I checked, and the relay is energizing.
so I figure I have a bad clutch.
I pulled the compresor
I have not been able to remove the clutch from the compressor
and I cannot find a replacement clutch at any local auto store.
I figure I should just buy a new compressor with clutch.
any thoughts on where I can get the best price?

 

Did you check with a test light across the coil at the socket at the compressor? there could also be a bad return or ground wire.
Use a DVM and check the resistance of the coil and be sure it's bad before you tear it apart. Not for sure but I would imagine it would be around 1 or 2 ohms resistance.
You might be able to find just the coil at some auto parts or a good AC repair shop or even a junk yard. You need a special puller that screws into the front of the clutch plate and it pushes the clutch off, (OTC sells these.) it also pulls it back on. Don't try to use a gear puller because you will screw it up. Also when you reinstall the plate you need to set the gap on the plate. That is a no big.
Good luck. Jim

http://www.otctools.com/newcatalog/products/256_1.jpg

 

SBEC means, Single Board Engine Controller, or computer. They are hidden inside the drivers front fender behind the battery. The dodge SBEC doesn't contol the engine like a true electronic diesel on these trucks it really just helps run accessories.

If you don't have power at the clutch but have good ground check to see if the low pressure switch is allowing current through it or jumper it to see if power is then present at the compressor clutch. Do this while the ignition is in the run position with the A/C controls on.

The A/C compressor for these 89-93 trucks has a different clutch than a gas motor because the belt has a few extra ribs. Everything is supposedly different on 94 up. A few months back I bought a spare clutch assembly from dodge (no aftermarket that I could find) as the were reportedly only 41 left in the warehouse and they were a "discontinued" item. Reman compressor availability is kind of sketchy as well.

Hopefully the clutch is good, they are very pricey!

 

thanks for all the helpfull hints.
I checked and there is voltage going to the compressor to engage the clutch.
and the clutch coil is not open circuit.
I decided to buy a new compressor and clutch.
I could not find the unit for the 91 cummins, but I noticed it is the same compressor as the gas version the c 171. The clutch looks similiar, so I pulled the pulley and put it on a rebuilt c 171 compressor for the 8 cylinder engine.
the coils look similar, and this unit was only $170.00 compared to 400 for the cummins rebuild.
will this work?
Am i fliting with disaster?
I guess I will know soon

 

I'll bet the compressor is the same. Just switch on the 8 rib pulley clutch. Dodge just bought the compressors from a manufacturer (Sanden?) and had to fit them to many different engines.