a/c problem

[jdurham]

Here we go again



I emptied my a/c system (134A) to replace my heater core. Put it back together, took it to have it charged. They pulled a vacuum, no leaks, shot a charge to it. Fired it up, kicked on the a/c, compressor clutch wouldn't engage. Checked pressure switch, had 12V to it and out. Checked lead at compressor, had 12V. Jumped the ground wire to ground, and the clutch clicked. I couldn't find any reason for the ground to do this, but it would open when the key was cut on. Thinking it might be a computer, I disconnected my battery for a minute and reconnected, no help. Have any of you guys run across this? I've been trying to figure it out, but now look like this .



Thanks,



Jim

 

[Wayno]

I don't think the AC goes through the computer . You need to chase the ground wire back and see if you lost ground somewhere . I put some freon in a Escort last summer and I couldn't get the compressor to kick on either , even after I jump the cut out switch . I ran a hot wire over to the battery and a ground wire to the battery and after I got about two cans of freon in it I put the factory plug back on and it work . It about drove me crazy for a bit . Never could figure out why there was no 12v or ground to the clutch after I bypass the low freon switch . You might want to check the wires on the expansion valve .

 

[Paychk]

The relay right in front of the hood hinge on the drivers side feeds the A/C clutch, it is controlled by the PCM. The wire that is dark blue with black stripe goes to clutch. The power flow from the A/C low press switch then goes to the A/C cycling switch, it is near the right inner fender area and shows a probe coming out of it. I would think that it goes into the A/C housing some where. From the cycling switch it goes to the PCM.



If you need more let me know and I can look it up in my manual.

 

[Wayno]

Well I am curious now . Does the ground wire go through the relay too . He said he had 12v going to the clutch but no ground . I have always been told that the PCM only control the alternator , speedometer , overdrive and the cruise ?????

 

[jdurham]

Well, let me add some additional info. The guy did charge the system, so it has r134a in it, so the pressure switch shouldn't be a problem. I pulled the wires off of the switch, and there was 12 volts to one, and the switch was closed. Plugged it back in, and the connector by the compressor had 12V. Am I right in assuing that if there is 12V to the compressor, that I can rule out both the pressure switch and the cycling switch? Also, where i was working on the truck, they had a Mitchell manual on cd, so he printed awiring diagram for the a/c. I was even more confused since it appeared that the blue wire was ground, and the brown was hot. It also said the blue wire went through the wiper motor (which is working), but I'm not sure that's correct. I'll try to check the relay on the drivers side fenderwell today, or tomorrow and get back with you guys. Thanks a lot for the input!



Jim

 

[Paychk]

Jim

If you are getting 12V to the compressor then everything else is working, at least enough to get the compressor to run. I'm confused by the

it appeared that the blue wire was ground, and the brown was hot

where are these 2 wires at? the compressor disconnect should have 2 black wires, power in 1 the other is ground.



Wayno

If you go here:



https://www.turbodieselregister.com/user_gallery/displayimage.php?&photoid=3751&width=4



and look at this diagram you will see all outputs from the computer on the right half of the large square. In fact the left side of the square are all inputs to the computer.

 

[Wayno]

I wonder , could you bypass the PCM and get 12V to the clutch the old fashion way ???? if your PCM ever went out ???? You might have to put the old type expansion valve on it tho. Good picture Paychk .

 

[jdurham]

Well, I looked it over, and there is only one relay on the left fender well. I jumped it and the truck tried to start. I now know where the starter relay is, but not the a/c relay. Did I mention this is my 90 model? Anyway, it does have 12V to one of the comressor leads, but the cluch won't work. If I jump the other lead to ground, the clutch engages. Still haven't figured it out...

 

[Paychk]

Jim



I boobooed, I thought you were working a 92/93, everything I have written is for those trucks with a PCM (computer). I don't have a manual for the early trucks and my 89 is so buried under junk I couldn't lift the hood to look, even to save my life. My bad, sorry:{

 

[Wayno]

On my 1983 Dodge truck the ground wire went to a small bolt on the compressor . The 12volt went through the ignition switch . I burn up a few ignition switches and a bunch of blower motor switches . I had to replace all the wiring at plug on the ignition switch finally cause all the wires were burnt . I am not 100 percent sure but I think the 89 and 90 have about the same wiring as the early 80 models . Did you leave any ground straps off anywhere ??????

 

[jdurham]

Wayno,



I have heard of so many ground problems that I checked them while I was working on it. I didn't find any. As for the way it is wired, there are 2 wires coming out of the compressor, and neither is grounded to the compressor. Does anyone have a wiring diagram for a 90 with Cummins?



Jim

 

[LDM]

I have the same problem on my 90 model. The ground circuit indeed goes thru the cycling switch at the expansion valve. My problem seems to be the expansion valve stuck open or possibly the orifice may be plugged which is creating a low pressure condition and thereby the low pressure switch has the ground circuit open going to the compressor.

 

[jdurham]

LDM,



I agree that the ground goes through the switch, and I can't seem to find the problem.





AGAIN - anybody know where we can get a schematic for a 90 model a/c system?

 

[RSchwarzli]

A/C problem ?

I will check at home tonight for a schematic for a 1990 A/C system. It is possible that it may be in my service manuals. If you could e-mail me with your fax number, I will send you a photo copy. I have no means of scanning and placing it on this site. sorry. I,ll get back to you tomorrow.



Bernie

 

[RSchwarzli]

Re: A/C problem ?

Originally posted by BSchwarzli

I will check at home tonight for a schematic for a 1990 A/C system. It is possible that it may be in my service manuals. If you could e-mail me with your fax number, I will send you a photo copy. I have no means of scanning and placing it on this site. sorry. I,ll get back to you tomorrow.



Bernie

Hey Jim, you're in luck. My 1990 Dodge service manual does have the wiring diagrams that you are looking for. Oo. E-mail me with a fax number so that I can sent you the copies Friday.

P. S. I'm leaving for Alabama Monday and will not be back for 2 weeks. Hope to send it before then.



Bernie