AC Issue - JeepForum.com
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post #1 of 19 Old 06-13-2020, 08:27 AM Thread Starter
mikewhite
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AC Issue

Hello all,

I have run into an issue with the AC system in my 1999 Cherokee 4.0 Sport. I think I know what the problem is but I am not sure how to proceed.

The AC does not blow cold air at all, regardless of how long the engine has been running, outside temp, etc. I have confirmed that the system has refrigerant and pressure and that the compressor clutch is engaging (sporadically but I see it spinning). I ran into the same issue some years ago and I recall my mechanic saying there is a gate in the vent system that switches between cold and hot air. I am certain there used to be a "ka-thunk" sound coming from the vent shortly after switching the climate control from heating to air conditioning, followed shortly thereafter by blessed cool air. :-)

Does this sound familiar to anyone? If so how do I diagnose and repair the problem? I am currently unemployed and trying to spend as little as possible but I need to get this resolved.

Thanks!

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post #2 of 19 Old 06-13-2020, 08:36 AM
jtec
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confusing - you are in the Cherokee XJ forum, under your name it says "1999 FSJ cherokee"
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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 #3 of 19 Old 06-13-2020, 08:55 AM
jtec
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thinking this is a 1999 Cherokee XJ a common issue is blend door -

This is a link to info - will describe quick fix and improved parts. A picture is worth 1000 words; let us know. There is another source for these fixes but these people (kits) have worked for me.

http://heatertreater.net/jeep-cherokee

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 #4 of 19 Old 06-14-2020, 05:06 AM Thread Starter
mikewhite
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I apologize. I made a mistake. It is an XJ.

Thanks for the info about the blend door - that is exactly what I was looking for.
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post #5 of 19 Old 06-22-2020, 01:52 PM Thread Starter
mikewhite
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UPDATE: I replaced the blend door and confirmed that is now working. Still no AC!

It looks like the compressor clutch is no longer engaging. I used a paperclip to bypass the low-pressure switch but the clutch still does not engage.

I checked the fuse for the climate controls (#25 if anyone is interested) and that is still intact.

I re-checked the low pressure valve and that still registers decent pressure.

I'm hoping I don't need to replace the compressor. Any thoughts?
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post #6 of 19 Old 06-22-2020, 06:35 PM
jtec
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OK this is a 1999 cherokee XJ with a 4.0L eng?

ideally you should check the AC pressures HIGH and LOW with gauges.

AC compressor (load) is fuse #20 a 20amp fuse in the PDC.
AC compressor (control) is fuse #10 a 15amp in the junction box- in cab fuse box.

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 #7 of 19 Old 06-23-2020, 07:33 AM Thread Starter
mikewhite
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Hey JTEC. Thanks for the info. I checked the #20 fuse in the PDC and the #10 fuse in the junction box. Both are intact.

I noticed that there is an "AC Compressor Clutch Relay" in the PDC. Could that go bad and cause this problem? Is there any way to check that?
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post #8 of 19 Old 06-23-2020, 07:53 AM
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the relay is a great place to ck circuits for AC. A test light and we can ck - relay control circuit and comp 12v supply

ANSWER - swap with a similar relay, hopefully horn, wipers, are the same for testing.

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 #9 of 19 Old 06-24-2020, 09:44 AM
jeepjeepster
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Check to see if the compressor is getting 12v. If it is, smack the center of the A/C pulley with the handle end of a hammer if you can safety get to it while the engine is running. See if that makes the clutch engage when you have the A/C turned on and the low pressure switch is bypassed.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #10 of 19 Old 06-24-2020, 10:15 AM
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Do you have a gauge set? If not get one. The static pressure can be as high as 60psi, yet when the compressor engages it can drop below 20psi. That causes the low pressure switch to cut the compressor off. As static pressure builds back up the compressor engages again, cuts off again, etc, and you have no cold air. If the charge is very low the compressor will never come on. The correct procedure is to purge the system completely, vacuum it down with a vacuum pump to get any moisture out, then recharge with the correct amount. If all else is good you should get proper AC. But without doing that you are guessing about everything else. .
downs likes this.

Mark in Queens- Home of Spiderman and the Ramones
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post #11 of 19 Old 06-25-2020, 03:13 PM Thread Starter
mikewhite
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Quote:
Originally Posted by jtec View Post
the relay is a great place to ck circuits for AC. A test light and we can ck - relay control circuit and comp 12v supply

ANSWER - swap with a similar relay, hopefully horn, wipers, are the same for testing.

I tested the relay: connected terminals 1 and 2 to the battery and heard the click of the electromagnet engaging. Checked continuity across terminals 3 and 5 on the relay: no resistance when the relay is engaged. I didn't see any similar relays I could test with.
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post #12 of 19 Old 06-25-2020, 03:19 PM Thread Starter
mikewhite
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Quote:
Originally Posted by jeepjeepster View Post
Check to see if the compressor is getting 12v. If it is, smack the center of the A/C pulley with the handle end of a hammer if you can safety get to it while the engine is running. See if that makes the clutch engage when you have the A/C turned on and the low pressure switch is bypassed.
Smack it with a hammer! I can get behind that! I thought of that too but the front of the compressor is immediately behind the cowling for the fan blade. Hard to get to safely.

Good idea. I have not checked to see if the compressor is getting 12 v. I'll need to dig around a bit to find where I can check that.
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post #13 of 19 Old 06-25-2020, 03:24 PM Thread Starter
mikewhite
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Quote:
Originally Posted by Fourspeedman View Post
Do you have a gauge set? If not get one. The static pressure can be as high as 60psi, yet when the compressor engages it can drop below 20psi. That causes the low pressure switch to cut the compressor off. As static pressure builds back up the compressor engages again, cuts off again, etc, and you have no cold air. If the charge is very low the compressor will never come on. The correct procedure is to purge the system completely, vacuum it down with a vacuum pump to get any moisture out, then recharge with the correct amount. If all else is good you should get proper AC. But without doing that you are guessing about everything else. .
Good suggestion but I'll need to find someone I can borrow that from. I am currently unemployed so I need to get this AC situation resolved on the cheap.

I did try to bypass the low pressure switch by sticking a paper clip into the connector and running the AC. I have seen folks on several videos do that. Maybe I can try the same procedure on the high pressure switch?
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post #14 of 19 Old 06-25-2020, 05:46 PM
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No, the high pressure switch is normally closed so it can cut the compressor off if the pressure opens it. The low pressure switch is normally open but closes with sufficient pressure. By shorting it you are fooling the system into thinking there is pressure to operate. Find out if the wire to the compressor is getting 12 volts then try shorting the low pressure switch. If there is any freon at all you should get some cooling. But it is better to borrow some gauges and know for sure.

Mark in Queens- Home of Spiderman and the Ramones
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post #15 of 19 Old 06-26-2020, 06:08 AM
jeepjeepster
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Quote:
Originally Posted by mikewhite View Post
Smack it with a hammer! I can get behind that! I thought of that too but the front of the compressor is immediately behind the cowling for the fan blade. Hard to get to safely.

Good idea. I have not checked to see if the compressor is getting 12 v. I'll need to dig around a bit to find where I can check that.
As the compressor wears, the clutch may not engage when power is applied. I've seen them where the gap is just a bit too big for the magnet to pull the clutch in. A slight tap makes it pop right in. Just something to check that can throw you for a loop.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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