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Unread 06-28-2013, 04:07 AM   #1
RABBIDCOW55
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1999 XJ Cherokee 
 
Join Date: Jan 2013
Posts: 76
A/C Low Pressure Switch Jump

Hi all,

I wrote a previous post about my AC being finicky. I got some great responses but now I need some help with the tests, specifically "bypassing" the low pressure switch to see if my clutch engages when the engine is hot and it turns off. I am just not sure which plugs to cross or which ones to test for voltage. I've read through a bunch of old posts but there aren't any walk throughs for how to actually do this test. I'm a visual learner so any pictures or videos would help a lot, just hit 103 today!!!

99 XJ 4.0 4x4

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Unread 06-28-2013, 04:44 AM   #2
CCKen
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1999 XJ Cherokee 
 
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Quote:
Originally Posted by RABBIDCOW55 View Post
Hi all,

I wrote a previous post about my AC being finicky. I got some great responses but now I need some help with the tests, specifically "bypassing" the low pressure switch to see if my clutch engages when the engine is hot and it turns off. I am just not sure which plugs to cross or which ones to test for voltage. I've read through a bunch of old posts but there aren't any walk throughs for how to actually do this test. I'm a visual learner so any pictures or videos would help a lot, just hit 103 today!!!

99 XJ 4.0 4x4
You will want to jump the two pin cavities in the Low Pressure Cycling Switch on top of the AC Accumulator (see pic). Use a paper clip to jump the cavities, but do not shove the clip wires into the cavities unless you hammer or file the wire ends down so they fit the cavities snugly but do not expand them too much.

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Unread 06-28-2013, 04:59 AM   #3
RABBIDCOW55
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Just what I was looking for also, if it does end up being a bad pressure switch, do I have to completely evacuate the system or just be very quick with mt hands.... (that's what she said)
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Unread 06-28-2013, 05:53 AM   #4
CCKen
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Quote:
Originally Posted by RABBIDCOW55 View Post
Just what I was looking for also, if it does end up being a bad pressure switch, do I have to completely evacuate the system or just be very quick with mt hands.... (that's what she said)
Before changing the switch, you should determine if your refrigerant is fully charged. If, by jumping the switch the Compressor Clutch pulls in it doesn't mean the switch is bad. If the system pressure is too low a normally operating switch will open and shut the system down. Do you know how to check your system pressure?

Also, know that there is a AC Compressor Clutch relay in the PDC and a fuse in the PDC for the clutch relay, and a fuse in the JB for the clutch relay.

If you need to change the switch it can be removed and you won't lose pressure.
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Unread 07-01-2013, 09:50 PM   #5
RABBIDCOW55
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So I jumped the switch: no clutch engagment when hot. I swapped the relay from a working XJ: same story. Checked the pressure: 30lbs. I think next I'm gonna jump the high pressure switch on the compressor and run 12v to the clutch. Wish me luck
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