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Discussion Starter · #1 ·
2000 Dodge Intrepid 2.7. Issues with A/C. Put used compressor on and pulled vacuum and put freon in, no leaks. Clutch will only kick on with paper clip at relay. Put new pressure transducer on and still the same. Blows ice cold with paper clip at relay. Any clue on what to check now. Could expansion valve have anything to do with it? Worked until old compressor locked up. Fans work fine with no issue. If anyone has a thought on what it could be or what to check please reply.
 

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You might need to do some basic troubleshooting. Since shorting across the relay contacts causes compressor to run and cooling to occur, a good next step might be to swap in another relay or see if the relay coil is getting energized by PCM, and if not, why not?

You should have an FSM for the wiring diagrams, to understand how it works, to understand what inputs the PCM needs to energize the relay coil, etc.

Here's an example of using the wiring diagrams for troubleshooting from what you posted:

Is Fuse 21 blown? (measure fuse with ohmmeter - visual inspection of the fuse is not reliable):
Rectangle Font Parallel Slope Number


This page shows the other loads on Fuse 21 - are the other loads working? Is fuse 21 blown and keeps blowing due to a problem with one of those loads (a radiator fan) or a short in the wiring?:
Schematic Rectangle Font Parallel Engineering


If fuse 21 is good, with relay installed, ground terminal C of relay. If compressor runs with terminal C grounded, then you need to find out why PCM is not energizing the relay coil thru terminal C.
 

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Discussion Starter · #3 ·
Thanks for the reply. I have swapped relays and they are fine. May just throw another compressor on it and see just for the heck of it. But if paperclip makes this one work then more than likely its not the compressor, Correct? What about ambient air temp sensor? About ready to give up on it. I do have a FSM but honestly dont understand wiring diagrams to well.
 

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You're welcome.

(1) You've proven that the compressor cools when forced on. Replacing the compressor at this point would be a total waste of time and money.

(2) The ambient temp sensor has no role whatsoever in operation of the a.c. The sensor is used by the PCM to determine the alternator charging voltage (regulation) set point and to provide ambient temperature readout on the overhead display.

I would check for blown Fuse 21 as I described in my troubleshooting example. And, again, don't rely on a visual check of the fuse - check it with an ohmmeter. The PCM grounds terminal C of the relay to close the relay contacts to run the compressor. If Fuse 21 is blown, there's no 12 volts to the other side of the relay coil, so the relay contacts wouldn't close.
 

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Discussion Starter · #5 ·
Just checked fuse 21 with meter and it ohmed as good and was visually good. Could fan relay have anything to do with it? They do run fine when clutch kicks in on compressor. Also I can ease the transducer connector off and back on and the fans kick on.
 

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So it sounds like the relay is not receiving the command (grounded terminal C) from the PCM. You can check voltage at terminal C - should be 12 volts for a.c. off, should be close to 0 volts when compessor clutch is commanded on. It sounds like terminal C is staying at 12 volts. You could verify that if you short terminal C to ground (it won't hurt the PCM output to do that) that the compressor runs. If so, the question would be is the PCM output turning on (going to ground) but there's a bad connection between the PCM output and the relay, or is the PCM not issuing the command? If the PCM is not issuing the command, is the PCM bad, or is the PCM not seeing all the necessary inputs to issue the command? There should be a list of conditions in the FSM a.c. section that have to be satisfied for the PCM to issue the command. You said it's cooling when the compressor runs. One of the conditions is that the a.c. pressure transducer is showing that there's system pressure above some required minimum. Is it possible that the system charge is marginal - i.e., enough to cool some if the compressor is forced on, but not above the minimum required for the PCM to issue the command? There may be some interplay between the fan relays, fans, and PCM that could be involved. For example, I know that the PCM can sense if a fan relay is removed, and I believe that would cause the PCM not to turn the clutch on. That's just an example of the kind of thing that has to be looked at. Again, find the list of requirements for the PCM to turn the compressor on, and troubleshoot by that (assuming that you determine that the relay is not receiving the command but that if you ground terminal C, the compressor runs).

I can't talk thru all permutations of possibilities remotely. You've got to systematically troubleshoot it. That likely will require your being able to read and understanding the wiring diagrams and verifying things with the multimeter. I've suggested some of the more likely possibilities.
 

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Glad you got it working, BUT...

When you posted "Clutch will only kick on with paper clip at relay", I assumed that you meant across the contacts of the relay (which I stated in post no. 2). IF Fuse B was blown and you had shorted across the relay contacts, the compressor would not have run, and I would have said right away that Fuse B is likely blown. So what terminals, pray tell, did you put the paper clip across that turned on the compressor?

If shorting across the relay contacts, if Fuse B was blown, the compressor would not have run:
 

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Maybe he shorted relay pins A-D? Instead of B-D?
 

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Also Fuse "B" in the PDC is the power source for the radiator fans. You might want to make sure both fans are running and one isn't siezed, etc.
 

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Well that was the situation. Could use paper clip all day long to make clutch kick in. Someone told me to check that fuse and it was blown and was the problem.
You haven't said where you put the paper clip. I guarantee you that if Fuse B was blown, the compressor would not run if you jumpered across the relay contacts. To troubleshoot, you have to understand the reason for what you do.

Did someone tell you where to put the ends of the paper clip or did you just guess? When you said you put the paperclip at the relay, I assumed you knew where you put it and why. My mistake. 🤷‍♂️

Do you understand what the different pins of the relay and what the two fuses do? If you don't understand those things, the troubleshooting is going to be very inefficient and risks doing damage.

Maybe he shorted relay pins A-D? Instead of B-D?
I figured the same after it was revealed that Fuse B was blown. 🤦‍♂️ For some reason he's still not saying where he put the paper clip,
 
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Also Fuse "B" in the PDC is the power source for the radiator fans. You might want to make sure both fans are running and one isn't siezed, etc.
FWIW, Fuse B only affects the hi speed fan relay.
 
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