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Unread 06-14-2012, 05:09 PM   #1
360ci
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Jeep 5.9 A/C not working

Hi everyone New to this forum, but not new to Jeeps. I usually hang out on JeepsUnlimited, but the ZJ/WJ section has been pretty dead recently. I never bothered joining JeepForum because thus far I have been able to find everything I need by searching ...until now.

I picked up a sweet 5.9 on Monday and the a/c didn't work because the guy I bought it from said that he disconnected one of the a/c lines to replace the water pump. I had a vacuum pulled on it and had it filled and the compressor was running, but the air would not cool and the lined were hot. The mechanic told me not to run it because it could burn up the compressor. He also said it might be because the electric fan wasn't on or it could be the computer. I was thinking possibly the condensor? Any help is greatly appreciated because black jeep + black interior north carolina summer =

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Unread 06-14-2012, 05:25 PM   #2
SJZ
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Welcome to the Forum!
How were the pressures when the mechanic had the equipment on it?
If the A/C is on, the electric radiator fan should be running on LOW, at least. Do you get cool air when driving at hwy speed (cools condenser in lieu of cooling fan)?
Is the radiator fan cycling normally otherwise?
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Unread 06-14-2012, 05:53 PM   #3
360ci
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I don't remember the exact numbers, but he said they were what they were supposed to be. I tried it once on the interstate for a sec but still nothing. I usually don't have to drive on the highway, so I haven;t really had a chance to test it. As for the fan, I do know that it works because the night I got it, I took it rock crawling up the side of a mountain and the fan was running full blast by the time I got to the top, but that was before I had the system filled.
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Unread 06-14-2012, 06:06 PM   #4
SJZ
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Quote:
Originally Posted by 360ci View Post
I don't remember the exact numbers, but he said they were what they were supposed to be. I tried it once on the interstate for a sec but still nothing. I usually don't have to drive on the highway, so I haven;t really had a chance to test it. As for the fan, I do know that it works because the night I got it, I took it rock crawling up the side of a mountain and the fan was running full blast by the time I got to the top, but that was before I had the system filled.
One would think that the mechanic would get it running, or at least tell you what's wrong but...
If the pressures are where they should be with the compressor running, the lines should be cold. If you posted that they were cold, I would say that the trouble may be in the blend doors under the dash. Here's a link:
http://www.jeepforum.com/forum/f13/n.../#post13622466
If an A/C line was disconnected for a long while, the receiver drier should be replaced, and the system evacuated for a longer time before refilling. Are you sure the actual compressor is turning, and not just the pulley? Look at the center of the pulley to see.
acpress.jpg  
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___________________________________________
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'05 KJ Limited 3.7 Selec-Trac
'94 ZJ Limited 5.2 Q-Trac- sold, after 17 years
'67 International Harvester Scout 800; 345ci V8,T18 4spd, Dana 20 TC
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Unread 06-14-2012, 06:42 PM   #5
360ci
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Yeah the compressor was definitely running, but the lines were not cold at all. I actually burned myself by touching one of them. That's why I think its so strange.
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Unread 06-15-2012, 05:45 AM   #6
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Probably the electric fan. These tend to wear out the low-speed brushes.
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Unread 06-15-2012, 07:16 AM   #7
360ci
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Quote:
Originally Posted by Marcos View Post
Probably the electric fan. These tend to wear out the low-speed brushes.
So what you're saying is that if the low speed brushes are worn out then the fan will only work on high, and for the a/c to cool it has to run on low whenever the a/c is running.
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Unread 06-15-2012, 11:01 AM   #8
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If the clutch is cycling it should be cooling no matter what the fan speed right?

At least the lines should be cold if the clutch is working I would think.
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Unread 06-15-2012, 12:43 PM   #9
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One line will get cold temporarily when ac is running without the fan on. Did you touch both lines? Also, if you want to bypass the sensor, find the one on the upper left on the ac line and disconnect it. It's easy to find as the same wires connect to the upper radiator hose sensor. Short across the terminals with a wire and then turn your key to ACC position and the low speed fan should come on. If it doesn't, then address this first before spending a dime on the ac.
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Unread 06-15-2012, 01:53 PM   #10
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Quote:
Originally Posted by 360ci View Post
So what you're saying is that if the low speed brushes are worn out then the fan will only work on high, and for the a/c to cool it has to run on low whenever the a/c is running.
The way the fan circuit is designed, either the A/C pressure switch or the upper radiator hose switch will activate the low speed fan. The high speed fan will only be activated by the lower radiator hose switch.

If it is the fan, the A/C should cool if you cruise at highway speeds and then turn on the a/c. Might take a minute or two to start to feel cool.

There are 2 pressure switches on the A/C line from the compressor to condenser on the 5.9. One is normally open and is for the fan, it closes when pressure gets up to around 180psi. The other is the high pressure cutoff switch, which is normally closed and opens around 350 psi, to prevent system damage, and should pre-empt venting via the pressure relief valve. If the issue is something besides the fan, the HPCO should prevent further damage.
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Unread 06-15-2012, 03:05 PM   #11
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Quote:
Originally Posted by Marcos View Post
The way the fan circuit is designed, either the A/C pressure switch or the upper radiator hose switch will activate the low speed fan. The high speed fan will only be activated by the lower radiator hose switch.

If it is the fan, the A/C should cool if you cruise at highway speeds and then turn on the a/c. Might take a minute or two to start to feel cool.

There are 2 pressure switches on the A/C line from the compressor to condenser on the 5.9. One is normally open and is for the fan, it closes when pressure gets up to around 180psi. The other is the high pressure cutoff switch, which is normally closed and opens around 350 psi, to prevent system damage, and should pre-empt venting via the pressure relief valve. If the issue is something besides the fan, the HPCO should prevent further damage.
Correctomundo... nice to see someone else understands the stock fan setup on a 5.9. I'd like to add that the second relay (high speed) is placed in the circuit where it will always disable the low speed fan when it enables, no matter what the state of the pressure switches are.
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Unread 06-15-2012, 05:58 PM   #12
SJZ
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Quote:
Originally Posted by Marcos View Post
There are 2 pressure switches on the A/C line from the compressor to condenser on the 5.9. One is normally open and is for the fan, it closes when pressure gets up to around 180psi. The other is the high pressure cutoff switch, which is normally closed and opens around 350 psi, to prevent system damage, and should pre-empt venting via the pressure relief valve. If the issue is something besides the fan, the HPCO should prevent further damage.
The low pressure (clutch cycling) switch is on the accumulator, it opens below ~20 psi, and closed at ~35 psi. It is in series (electrically) with the high pressure cutoff, located near the compressor, and makes up a circuit that goes from ground to the PCM's A/C sense input. This input is either open or closed. On the 5.9, there is an additional wire that goes from the ungrounded side of the high pressure switch, to the ignition relay's coil. This is for cooling fan operation. The high pressure cutoff is closed below 270 psi, and opens at ~450 psi.
EDIT: This was a little confusing to me, as I'm going by the schematic in the FSM. I just noticed that you say there are two switches in the high pressure line. So that additional; wire I mentioned above goes to another switch. Sorry for the poor reading comprehension, but this epiphany has cleared my head & I can now rest easy...thanks!

When the system is is sitting with the A/C off, & refrigerant levels are proper, both the low & high pressure switches will be closed. Turn on the A/C, and the compressor runs, reducing the pressure on the low side and raising the high side pressure. When the low side declines to ~20 PSI, the low pressure switch opens, un-grounds the circuit to the PCM, which cuts power to the compressor. When the compressor cuts off, the low side pressure rises again & when it hits ~35 psi, the low side switch closes, grounding the circuit to the PCM & the compressor runs (if the PCM wants it to). This cycle goes on and on, which is why the low pressure switch is called the clutch cycling switch.
The only time the high pressure switch opens is when the compressor discharge pressure gets too high. I would think that most Jeep's high pressure switch never opens.
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"Those who hammer their guns into plows, will plow for those who do not." -Thomas Jefferson
___________________________________________
'98 ZJ Laredo 5.2 Selec-Trac (249 to 242 swap)
'05 KJ Limited 3.7 Selec-Trac
'94 ZJ Limited 5.2 Q-Trac- sold, after 17 years
'67 International Harvester Scout 800; 345ci V8,T18 4spd, Dana 20 TC
'06 Chrysler 300C SRT8 6.1L

Last edited by SJZ; 06-15-2012 at 06:21 PM.. Reason: wrong info see EDIT
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Unread 06-17-2012, 10:32 AM   #13
360ci
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Ok, I finally got the chance to mess with it today. Just having the a/c on, the fan didn't come on, but when I bypassed the sensor it did. Also, the small line that runs from the condensor to the firewall did get cold, but the two on the compressor never did. The air coming from the vents never got cold either.
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Unread 06-17-2012, 11:08 AM   #14
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That's how it's supposed to work. The only cold line is the one you mentioned and it's the part of the line after the expansion valve. Once the compressed gas get's passed the valve, it runs very cool.

So your issue can be two things: Bad sensor on AC line (confirmed) and /or bad upper hose sensor. As far as I can tell, they're no longer available or are very expensive for any that are still left around. I'm looking at fan controls, but for temporary use I've shorted/ bypassed the sensor on the upper hose so the low speed fan is always on. Runs just a bit over 210 and doesn't overheat.
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Unread 06-17-2012, 12:01 PM   #15
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With a properly functioning system, the hard line from the condenser to evaporator, as well as the Accumulator and suction lines all the way to the compressor should get cold.
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