QuestionQUESTION: 1995 Dodge Neon: ... Been diagnosing my A/C (won't run, properly charged) and thought it was the Evaporator Probe. Tested the connector and found no power between pin #1 & #3 which indicates there's no power coming from the Powertrain Control Module. Checked the wire at the PCM (brown/orange) for power (to ground) and the A/C engaged (with that wire grounded). I think by doing that I bypassed the control circuit. Do I need to get a new PCM or is there some way to bypass it? There's supposed to be power at that wire coming from the PCM.
Would really appreciate your advice!
ANSWER: Hi Jim,
I see that you must have the manual, based upon your statement "...indicates there's no power coming from the powertrain control module". I don't believe that the pcm actually provides power on that wire (as the manual claims) but rather it looks for power to be present (it is called AC sense) which indicates that the evaporator probe is happy with the fin temperature as are the pressure sensors.
Does your manual also show a 7 step evaporator probe test, and have you done it? I can't corroborate the accuracy of that test but none the less try it.
The fuse that powers the circuit (#8 in the fuse block) that passes through the fan probe and then is shared to the mode switch, and also to the path through the high and low pressure switches to pin 38 at the pcm. I would check that fuse and that its voltage is appearing at pin 2 of the probe when the key is in the run position.
Then check that voltage is also present at pins 1 and 3 which it should be unless the probe is iced. Abd finally check that it gets to pin 38 of the plug with the pcm plug removed.
Let me know what you find and we'll go from there.
Roland
PS Please 'rate' my answer, and where you see the question about a nomination of me to be 'volunteer of the month' consider a 'yes' answer. Thank you
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QUESTION: I'm following TSB 24?20?94 (seven steps). Paragraph #2 states "disconnect the 3 wire connector from the clutch cycling switch. Paragraph #3 says turn everything on (A/C) and check for voltage between pin #1 and #2. (This check is good, I have power from the ignition circuit (white wire). Paragraph 4 states "Test for voltage between pin #1 and pin #3 on connector #C403. If no voltage is detected, then there is no voltage coming FROM the PCM (refer to the service manual wiring diagram, page 8W?42?4).
No power at the low pressure switch connector (with or without the evaporator probe connected). Both switches (low & high) are closed. I checked them with ohm meter.
I'm stumped. It sounds like the PCM is supposed to provide the power through the high and low switches back to the probe connector (pin #3).
You have no idea how grateful I am for your help!
ANSWER: Hi Jim,
I disagree with whoever wrote that text. It appears to me that if you have 12v on the white wire at pin 2, then the only possible uses for that voltage are for the sensor to pass that along to pin 38 at the pcm (via pin 1 at the output of the sensor and then through the two pressure sensors in series). If you aren't getting 12v out at pin 1 then I believe the sensor has failed. It should only fail to pass the 12v if the sensor is frozen. Similarly, though it isn't discussed, I would believe that if it doesn't show 12v pin 3 then the mode door would not operate and divert the air as you would choose it to be.
I am not certain why that mode door power is directed through the sensor but I am sure why it goes through the 'sense' circuit to pin 38 because without voltage at pin 38 the pcm will not activate the ac compressor (because the fins are thought to be iced) and that is the main purpose of the fin sensor.
Roland
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QUESTION: I checked for power at the high pressure switch with the A/C controls on and I have battery voltage through the switch but, no power at the low pressure switch.
I have a tendency to agree with you about the probe but frustration has set in. Maybe I'll give it another shot tomorrow.
AnswerHi Jim,
I am confused about what you mean by 'power at'. As I read the wiring diagram the 12v should be on pin 3 at the fin sensor dark blue/orange if the sensor is good, then at the other end of the wire at low pressure switch on the firewall it should be also 12v. Then if the pressure is adequate the dark blue/white wire should show 12v at the low pressure switch and at the other end of that wire, at the high pressure switch at the compressor you should see 12v and if the pressure is not too high you should see 12v on the brown/orange wire which then connects to pin 33.
Ooops, I now see a discrepency in my earlier answers in that the sense switch for '95 is at pin 33 while for '97 it is at pin 38. Sorry to not have noticed that!
But what was funny about your last report is that you mentioned voltage at the high but not the low pressure switch, while the 'flow' of the voltage in the circuit is from the low to the high, so I don't see how you can measure 12v at the high but not at the low? Where do you have the (-) probe of your voltmeter connected to?
Roland
