1996 XJ Faulty PCM Fixed (sort of) A/C issue - JeepForum.com
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Unread 07-10-2013, 06:25 PM   #1
JoeSo
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1996 XJ Cherokee 
 
Join Date: Jul 2013
Location: Lakeland, FL
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1996 XJ Faulty PCM Fixed (sort of) A/C issue

Been lurking around the forum for months and owe everything I know about working on my Jeep between this forum and my shop manual. Thanks guys, your help really is appreciated.

96 XJ Classic recently began burning through fuel pumps, until eventually it wouldn't start at all even with brand new fuel pumps (would not prime). Narrowed it down finally to a faulty PCM. Replaced the PCM from a junker (98 XJ Sport, same engine/trans, w/ A/C) and it worked like a charm, fired right up and has been running (a bit crazy right at first) perfect ever since.

The only problem is the A/C no longer worked after replacing the PCM, and still does not work to this day. Still blows air like it did before but no cold and compressor will not click on, neither will the electric fan. Relays/fuses are good and A/C worked perfect before.

This appears to be obviously related to the "new" PCM, but I'd like your advice on how to proceed. Do I need to program or reset this PCM somehow? Anyway to avoid a costly trip to the stealership? Am I missing something obvious?

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Unread 07-10-2013, 08:28 PM   #2
1CleanTJ
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1999 TJ Wrangler 
 
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id start by jumping the low pressure switch, just to see if it will kick on. (engine running)

could also jump pin 87 and 30 on the a/c relay (engine running) to see if the a/c clutch is kicking in, this should also tell the fan to kick on.

with engine off, key out of ignition also try turning the electric fan blade to make sure it isnt seized up.

could all be coincidence with the pcm change. easier to check and make sure its working before you decide to mess with the pcm and trace pin outs
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Unread 07-12-2013, 10:54 AM   #3
JoeSo
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Good call. I'll try jumping the relay tonight to be thorough. I did put a gauge to the a/c and it gave a reading of very high pressure- this may be what's keeping it from turning on, just need to find out why the high pressure.
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Unread 07-12-2013, 12:11 PM   #4
1CleanTJ
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Quote:
Originally Posted by JoeSo View Post
Good call. I'll try jumping the relay tonight to be thorough. I did put a gauge to the a/c and it gave a reading of very high pressure- this may be what's keeping it from turning on, just need to find out why the high pressure.
you really need to check pressure with it running, one side will be very high and other low.

start with making sure the compressor turns on first and work backwards from there
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Unread 07-19-2013, 01:43 PM   #5
JoeSo
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Quote:
Originally Posted by 1CleanTJ
start with making sure the compressor turns on first and work backwards from there
Jumped the pins on the ac relay, compressor and clutch would not click on. Any other way to check the compressor itself? What direction to head in now?
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Unread 07-19-2013, 11:09 PM   #6
AZ Jeff
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Quote:
Originally Posted by JoeSo View Post
Jumped the pins on the ac relay, compressor and clutch would not click on. Any other way to check the compressor itself? What direction to head in now?
Start by checking to see if you have 12V on one of the terminals to the pressure switch. If yes, then check for power at the clutch. If yes, then check for continuity at the clutch. If yes, then check for clutch air gap.
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Unread 07-20-2013, 04:17 PM   #7
1CleanTJ
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AZ-Jeff said it correct, you can apply power directly from battery to the single wire coming off the connector of the the a/c and see if it clicks on, it not could be air gap problem, which is pretty common. sometimes you can get the a/c compressor clutch to work again by hitting it with a hammer.... (obviously not super hard to crack it...)

On a side note, i went through all you did and ended up replacing my a/c compressor with a Junkyard one that was $25.. now I am enjoying ice cold a/c in this 98 degree humid heat we have been having
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Unread 07-20-2013, 06:24 PM   #8
JoeSo
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Quote:
Originally Posted by AZ Jeff

Start by checking to see if you have 12V on one of the terminals to the pressure switch.
Got as far as the pressure switch, just over 1 volt with the ac on. What would this indicate?

Hopefully this is a junkyard fix, the junkyard PCM I found that got it running was only $20!
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