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96 Neon SOHC A/C Electrical Problem

Jetboy55 on Sun July 29, 2012 12:37 AM User is offline

Year: 1996
Make: Plymouth
Model: Neon
Engine Size: 2.0
Refrigerant Type: R134a
Ambient Temp: 90F
Pressure Low: 35
Pressure High: 260
Country of Origin: United States

Just finished replacing my TXV, receiver/drier, and new gasket kit. When jumpered correctly for clutch engagement and radiator fans running, system works great and is nice and cold. However, the PCM is not turning on the compressor or the radiator fans (fans do turn on by coolant temperature thou). I have checked continuity through the low switch, high switch, and associated wiring, all good. I dont understand how the electrical portion works as it relates to the evap temp probe, mode switches in the dash, and how they all work to provide ground or power signal to the PCM. So far this is what I have seen: With system on, there is .18V at the brown/orange wire at the low pressure switch. It drops to .06V if I turn down the A/C knob to lowest A/C setting. Should this wire (coming from evap/cycling switch) have 12V on it? I guess for now I just need to know how this portion of the control wiring functions so I can troubleshoot it. Does the cycling switch provide a 12V source to the PCM (thru the pressure switches)? Or does the PCM send power up thru these switches, thru the evap sensor and down thru the wires to the mode dial where ground is provided anytime A/C or defrost is selected? I guess Im asking if the PCM wants to see a 12V source on the pressure switch portion of the wiring, some other ??V source, or ground. Thanks for help in understanding this control system so I can troubleshoot it. Thanks again.

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Aircraft Technician and Inspector for 20 years.

Edited: Sun July 29, 2012 at 12:38 AM by Jetboy55

Dougflas on Sun July 29, 2012 7:30 AM User is offline

Do you have the schematic of the system? If not, are you aware that you can purchase a CD with everything about your vehicle including engine/drivetrain and electrical for less than $50.00? Michell produces them and I think this site offers them.

Jetboy55 on Sun July 29, 2012 11:36 AM User is offline

I do have a basic schematic from my Haynes manual, however it does not give pin numbers. I have been able to find pin numbers for troubelshooting on different forums and other peoples troubleshooting. I wish I could afford to buy the manual you mentioned but I cant right now. ....My las post was a little scatter brained, I'll try to summarize. It seems that the PCM is looking for one of two possible conditions on the brown/orange wire that comes into it from the pressure switches....Possiblility 1) 12V (or a lesser voltage) from Fuse 8 (10A) which feeds the evap (cycling) switch and by extension the pressure switches, or.... Possibility 2) Ground provided thu the same pressure switches, the evap sensor, and the mode dials in the dash which provide ground whenever A/C or Defrost is selected. The problem is, I dont know which possibility is the way the circuit functions. It seems to me that if the PCM was looking for Possibility 1 - voltage, then it would see it all the time (assuming evap is not frozen up and all the switches are in working order) and thus run the A/C all the time reguardless of whether A/C was turned on or not. So I'm leaning toward possibility 2 which would allow the PCM to not only respond to the switches and evap sensor, but also the mode dial so it could see when the user actually turns on the A/C. I tried to jumper the PCM brown/orange wire at the high switch to ground to test my theory, but it didnt work, but that wire from high switch to PCM has not been tested for a open yet, so that could still be the possibility. I would test that brown/orange wire from high switch to PCM plug for open, however I dont know the pin number and which of the two plugs its in, at the PCM. Anyone know? Thanks again.

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Aircraft Technician and Inspector for 20 years.

Edited: Sun July 29, 2012 at 12:01 PM by Jetboy55

Jetboy55 on Sun July 29, 2012 2:41 PM User is offline

I got the pin numbers and plug info from the neons.org forum so now I can test that. Im still wondering how the system works, does the PCM want to see 12V (Possibility 1) or ground (Possibility 2). Thanks again.

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Aircraft Technician and Inspector for 20 years.

Jetboy55 on Sun July 29, 2012 7:16 PM User is offline

With the pin numbers I was able to test from high switch to PCM, turn out its open. Replace the wire and the A/C now works as it should. So it turns out the PCM is looking for a ground on that wire, not 12V. Now the only problem is that it is'nt all that cold. Its cool, definately better than before I did all this work, but just cool. My SnapOn cart says I serviced with 1lb 13oz's of refrigerant, so it is properly charged. I wonder if I shoudl charge it using a different method besides weight. Ive never done it any other way on the aircraft I work on. Any suggestions? I wonder what the problem is?

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Aircraft Technician and Inspector for 20 years.

Edited: Sun July 29, 2012 at 7:21 PM by Jetboy55

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