1998 XJ AC issue - clutch doesn't turn on unless I jump it- blows cold when jumped

blondejoncherokee

blondejoncherokee

NAXJA Member
Location
sacramento
1998 XJ
AC used to work - now the clutch wont engage no matter what I do.
then one day it stopped, replaced relay and fuses and still nothing.
had a shop charge it while I jumped the hot for the AC straight to the battery, it blew cold after that when I jumped it.

Jumped HP and LP switches and it didnt seem to do anything. I can jump it at that relay and it'll kick the clutch on but that is simply just giving the clutch 12V, which is bypassing everything.

any ideas?

Replaced the metal line with the orifice last year when It wouldnt work, and I cant remember if I replaced the Drier or not.
 
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Sounds like a loss of connection to the PCM, I would start by doing a volt check at the individual pin-outs at the PCM.
 
Yeah so the pcm signal at the ac relay with the ac on is battery voltage . Pretty sure the ecm sends a ground signal when the ac is on. Might jump that wire to ground and see if it powers on. Then i know to work from there back
 
blondejoncherokee said:
Yeah so the pcm signal at the ac relay with the ac on is battery voltage . Pretty sure the ecm sends a ground signal when the ac is on. Might jump that wire to ground and see if it powers on. Then i know to work from there back
Click to expand...

I'd check to see if you have ground on pin C22 (Switch sense pin for low and high pressure switches) of the PCM, if you have ground there, then try grounding pin C13 and see if the compressor kicks on. Also C23 is the A/C request pin from the HVAC control, which should get grounded when you request A/C. :farmer:
 
I thought c13 was not used ?
 
Shows as C1 on the jtec diagram
 
Does the ecu use the fan sensor as an input ? I do have my fan wires to its own relay. But pretty sure its been like that since ive owned it.
 
Seems like this thread is over complicating the problem. Your problem is most likely the low pressure switch. I have had to replace a couple of them on different vehicles over the years. If they sense the pressure is to low it shuts off the compressor so it doesn't burn out. If it's bad then there is your problem.
 
nrwphoto said:
Seems like this thread is over complicating the problem. Your problem is most likely the low pressure switch. I have had to replace a couple of them on different vehicles over the years. If they sense the pressure is to low it shuts off the compressor so it doesn't burn out. If it's bad then there is your problem.
Click to expand...

I thought the same thing, but then took a closer look, and post #1 says he jumped that switch (as well as the hp switch) to no avail.
 
I'm not sure if the 98 does the same thing as mine. but when the a/c is active the cooling fan turns on. if neither the fan or compressor turn on its might not be getting the signal from the pressure switches. if the fan is on and not the compressor then its likely a wiring issue to the control side of the relay.
 
My snap on “red brick” scanner displays the ac switch on/off and an ac request. I think the ac switch is from the dash ac panel but not sure where the ac request gets generated. Maybe from ECU?
 
SO the High pressure switch has a 12V signal when I pull the plug off the thing and test the plug. The Low Pressure switch when I pull off the plug has no Battery voltage at either side- is the Low pressure switch in line with the high pressure switch so that has to send voltage over to the LP switch ?

I jumped the clutch to the battery - and put some gauges on it today, HP side is over 200 and climbed up to 250 and we turned off the AC. LP went lower. SO it has a major blockage somewhere, and possibly bad wiring to the LP switch.

Im going to order some new components like a drier, orifice tube, and compressor and condenser, since the system also had a ton of oil in it. So its sort of weird what is going on, big blockage on HP side, but also too much oil. weird.
 
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Tha ac usually has i think about 7 oz of oil in it. Gray color is not good as it indicates metal filings .
 
I did not see grey , yet at least.

So I went to a buddies house and we did some testing with his power probe - it appears that the in dash switches work and that the actual High and Low pressure switches work themselves, but there seems to be an issue with something on the switch sense pin at the ECU.

If we put ground to the switch sense probe on the ECU, the compressor turns on. But I am seeing conflicting wiring diagrams, I dont know if the HP and LP switches are ground or Battery voltage, so Im not sure what we should be looking for there, but that is where we are at.

One wiring diagram shows the HP and LP switches in series, one shows just the HP switch feeding the switch sense pin on the ECU.

Does anyone know if both HP and LP switches are ground, battery voltage, or maybe one of each? It would help our testing.
 
dash switch appears to work, when we switch it from no ac to AC, the pin at the ECU switches to ground.
 
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