Intermittent A/C - JeepForum.com
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post #1 of 11 Old 08-20-2019, 11:36 AM Thread Starter
02Lightning
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Intermittent A/C

I replaced the low pressure and high pressure switches with junk yard switches. When the compressor kicks on the air is nice and cold. I just replaced the evaporator core also. I haven’t tried to track down a relay, but I will switch that with another one in the fuse box. I’m not sure it’s a ground issue, I would think I would have other problems. Any other ideas? This has manual controls by the way.


2001 Jeep Grand Cherokee Laredo 4.0L NV242LD Transfer Case, 42RE, 160,000 miles
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post #2 of 11 Old 08-20-2019, 07:39 PM
GmanWJ
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My 2002 had intermittent AC for years. Drove me nuts. Got mad one day and punched the temperature control knob on the panel. AC started working. A few more episodes convinced me that there was something wrong with the controls. Took it out, messed with it, cleaned it, didn't do much. Bought a replacement unit from a salvage supplier on ebay. Hasn't been an issue for more than 10 years now.
So that's a possibility.


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ok mostly just repairs, but we are closing in on a lift
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post #3 of 11 Old 08-21-2019, 06:18 AM Thread Starter
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Quote:
Originally Posted by GmanWJ View Post
My 2002 had intermittent AC for years. Drove me nuts. Got mad one day and punched the temperature control knob on the panel. AC started working. A few more episodes convinced me that there was something wrong with the controls. Took it out, messed with it, cleaned it, didn't do much. Bought a replacement unit from a salvage supplier on ebay. Hasn't been an issue for more than 10 years now.
So that's a possibility.
I'm starting to suspect, the controls myself.

2001 Jeep Grand Cherokee Laredo 4.0L NV242LD Transfer Case, 42RE, 160,000 miles
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post #4 of 11 Old 08-21-2019, 07:21 AM
jtec
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02Lightning What is the issue what does it do or not do?

DO you have tools- Gauges and a scanner ?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 11 Old 08-21-2019, 08:56 AM Thread Starter
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Quote:
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02Lightning What is the issue what does it do or not do?

DO you have tools- Gauges and a scanner ?
Everything works as it should, it just some times doesn't trigger the clutch on the A/C. When it works, it cools great. After I replaced the switches it worked for a week, then started not working again. I use Torque for codes, and it has no codes. But I'm not sure Torque will pick up A/C codes. I do have a set of harbor freight gauges.
I had an HVAC friend put 24oz. (as the hood states) of 134a in the system about a month ago, when I replaced the evap. core. When it quits working, I've pulled over and tapped on switches and wiggled wires with no results. Usually when I get ready to trace things down, it's starts working again.

I have tired sticking a screw driver on the clutch and pulley to see if it is magnetized when the engine is running and not running and got nothing.

2001 Jeep Grand Cherokee Laredo 4.0L NV242LD Transfer Case, 42RE, 160,000 miles
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post #6 of 11 Old 08-21-2019, 09:01 AM Thread Starter
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Today it's not working, but it could start working on my hour trip home from work and stay working for a few days.

2001 Jeep Grand Cherokee Laredo 4.0L NV242LD Transfer Case, 42RE, 160,000 miles
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post #7 of 11 Old 08-21-2019, 09:14 AM
jtec
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I asked about codes - some codes will prevent the PCM from commanding AC, temp issues and voltages come to mind.

It is NOT engaging AC clutch at the moment - we need to determine if PCM is controlling relay, OR if relay is closed and a wiring problem relay to clutch.
As I mention clutch can you check air gap?

As you have gauges - take a static pressure reading, with it not working the pressure is equal and called static - a low pressure would cause a no AC.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 11 Old 08-21-2019, 09:28 AM Thread Starter
02Lightning
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Quote:
Originally Posted by jtec View Post
I asked about codes - some codes will prevent the PCM from commanding AC, temp issues and voltages come to mind.

It is NOT engaging AC clutch at the moment - we need to determine if PCM is controlling relay, OR if relay is closed and a wiring problem relay to clutch.
As I mention clutch can you check air gap?

As you have gauges - take a static pressure reading, with it not working the pressure is equal and called static - a low pressure would cause a no AC.
It does have a P0420 pending code, but didn't think it was related to A/C. I can check air gap, but I don't know what it should be? In saying that, I should be able to tell if the electro magnet is magnetized and just not actuating the clutch.
Can I just jump across the low pressure switch plug, to see if anything happened? I thought I read where the PCM regulates voltage at that switch, and I could cause damage to the PCM by jumping it?

2001 Jeep Grand Cherokee Laredo 4.0L NV242LD Transfer Case, 42RE, 160,000 miles
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post #9 of 11 Old 08-21-2019, 11:42 AM
jtec
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lets check the pressure before jumping things, We could probe right at the relay for voltages.
Attached Files
File Type: pdf 01WJ AC relay.pdf (85.3 KB, 5 views)
File Type: pdf 01WJ AC pressure switches.pdf (95.3 KB, 4 views)
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 11 Old 08-21-2019, 03:02 PM
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As usual some real good info & diagrams jtec. To go along with those diagrams on the first one the AC relay ground is located at G104 on the rear passenger side of the engine block on the 4.0 near the oil dip stick tube. If the valve cover is leaking oil it's not uncommon for this ground to be oil soaked which isn't good.

On the 2nd diagram the AC low and high pressure switch grounds are on G108 located on the passenger-side inner fender near the PDC. And it never hurts to check/clean the PCM grounds on G103 to rear of motor mount on the passenger side of the engine block.

https://www.jeepforum.com/forum/f310...-info-4192594/

Granted if a ground is bad there may be other problems. But on the other hand it could just be a specific bad wire on that particular ground.

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post #11 of 11 Old 08-21-2019, 05:25 PM Thread Starter
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Ok, I am getting 12v on both wires at the AC pump. I hit the button to the off position, and the 12v goes away on the blue yellow stripe wire. I did find a loose ground behind the dipstick on the block. I tightened that, and the AC started working again. I got to believe the loose ground was my problem. Thanks guys for the help. I'll run it and see if my problem comes back.

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