My 5.9 '99 recently refused to turn on the A/C while on a trip. No current at compressor lead. I checked all fuses & relays to restore 12v to compressor lead, but all were good. A roadside tech checked and found refrigerant pressures normal. While idling as he was diagnosing, car began to idle roughly and progressively slower until it stalled. Check Engine light came on upon restart, still idled very slow and tried to stall. Code stated problem with O2 sensor but he didn't have one. He couldn't figure out what was wrong so we kept going, leaving selector switch in A/C position. Car ran fine at highway speeds. About an hour later, while driving along, all of a sudden refrigerated air started coming out of the vents. Twice more on trip A/C wouldn't work. When home I put in a new 02 sensor. A/C worked OK, front & back. Now, a month later, all symptoms are back. Scan states "hi-voltage sensor on bank one" is faulty (I don't remember the code, sorry). Summation: first the A/C won't turn on, but car runs normally, followed not long after by the C-E light and poor idling. What possible connection is there between the C-E light and the A/C system??

 

if computer detects(or thinks that it detects) a problem with the engine it may shut down the A/C to reduce the load on the engine, this i just a theory based on what i do know, however it sounds to me like you have a wiring problem if you are getting another 02 sensor code after replacing it, so i would start by looking for a short, or loose plug or bare wire, or anything else out of place in the wiring

 

Electrical issues.......Ug


Have the battery load tested and check the output amperage of the alternator. REALLY clean (to bare metals) the battery terminals and battery posts. Reset the PCM:

Quote:

To reset your engine codes:
Remove the negative terminal of your battery (10mm wrench).
Turn your ignition key to START and hold it there for about 15 seconds.
Turn your ignition key to OFF and remove it.
Connect the negative terminal of your battery.
Start but do not hit the throttle. Idle for about 10/15 seconds then turn off.
Restart the truck and drive as usual. It will take at least 12 starts and 48 miles to fully retune the computer. Hard Codes leave a shaddow for 40 full cold starts.

 

+1 on the battery and check your alternator.

 

Thanks for all the suggestions. I have cleaned the battery terminals (they were fine anyway) and both battery and alternator output test well within spec. Now, however, in addition to no A/C, there is a persistent missfire under acceleration. Any other ideas??

 

What code did it throw and which 02 sensor did you replace?

Also have you removed and cleaned the Throttle Body out yet?

 

Thanks again for your continued suggestions. The CEL code is "PO-132; o2 sensor bank one, sensor 1" However, that's the same code it threw last time, and changing the sensor only lasted a few weeks before the no-current-to-the A/C-clutch happened again, followed by poor running and the light coming on. There is only one sensor on the truck ('99 5.9) and I bought the correct OE one--not one that had to be spliced into the wiring. I can certainly understand that the t-body is probably dirty and could be making it idle poorly...but how can that affect current going to the A/C clutch???

 

One thing at a time......LOL

P0132 1/1 O2S Shorted To Voltage


That means that the harness you 02 sensor plugs into could be corroded. Look for power steering flid or any other corrosion inside the harness. Also it could mean you got a bad sensor. Go to a dealer ship for a new 02 sensor only.

There is 2 sensors on your truck. The code you threw is the pre-cat sensor. You will have one before the cat and 1 after the cat. You need to look again.


Also clean the TB. https://dodgeforum.com/forum/1st-gen...ttle-body.html


You might find you A/C issue goes away after your truck is running properly. Try not to over think.......

 

The mystery deepens. I cleaned the throttle body (really wasn't very dirty) and replaced the upstream 02 sensor. Still no A/C engagement, still occasionally goes into progressively slower idle until it stalls, when it again throws the CEL. There is also a persistent miss at 1500 rpm when driving (but not unloaded); when cold there are pops that come from under the hood, but go away quickly, and despite the steady-throttle miss, it will pull smoothly to over 4000 rpm with no missing. This thing is driving me nuts!

 

Did you take the Throttle Body off the truck and thoroughly clean it?


The only other thing I can think of would be a PCM. I think it's time to take it to a shop.