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post #1 of 38 Old 08-10-2020, 02:21 PM Thread Starter
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AC High Discharge Pressure

Hello everyone,


I am new to the forum and purchased a 2000 WJ 4.7L with 118k miles last fall. Early spring, I replaced the condenser and radiator as they were bent from some front end damage the previous owner had. Carfax said the evaporator was replaced at 80k miles. Now that summer is here, I have noticed that the Jeep was overheating on hot days. The temp gauge is reading above the middle mark only when the AC is running. I put a set of AC manifold gauges on it to check the pressures and noticed the discharge side is hitting the high pressure side at ~450psi.

Thinking there was a clogged line, I had the AC recovered and replaced the liquid line and receiver drier (blew out the evap when the lines were off, no blockage). Recharged again (24oz), same issue. Had the AC tech look at it with me and put his gauges on, still high discharge pressure. Unfortunately, not knowing the exact problem, I ordered a new compressor thinking it could be an internal issue. Still same issue now.

Here is what I have noticed though, when the engine is cold (sits overnight), the AC pressures look fine. Suction ~40psi, Discharge ~190-200psi. Once the engine comes up to temperature the discharge will slowly creep up to 450psi and start cycling and the water temperature starts to creep up over the 210degF mark. It does not overheat when the AC is off.

We have tried to take some charge out (6oz) and the discharge pressure still remains high. Add more in than required, still stays high. It doesn't seem to affect the final pressure. My radiator electric fan is new as well when I did the radiator. The fan relay is also new and it is running when the AC is on so the condenser has lots of airflow. I have even tried adding a box fan in front with no change on the high side pressure.

I have also taken some temperatures with the infrared temp gun:
Condenser in = ~100F
Condenser out = ~72F
Evap Out = ~47F (not easy to get a good reading)

There is condensation on the lines from right after the orifice in the liquid line to the suction side of the compressor and the jeep blows cold air. It just keeps tripping the high pressure switch and the jeep overheats at idle condition. My only other thought is the orifice is icing up or the evaporator is icing up and that is when the pressures start to rise. I would think this would go away though after letting it sit for a few hours with the AC off, but it takes a long time of sitting before the pressures return to normal (overnight usually).

Is the cooling system not able to handle the added load from the AC system? (my brothers 02 seems to have no problem with it, but it is the hydraulic fan)
Are the orifice tube designs just not as good as the expansion valve system?
I am wondering if the refrigerant is changing state since the liquid line runs close to the exhaust manifold on these jeeps?

I am at a loss and am hoping not to have to replace the evaporator since its a pain.

Any help or feedback is appreciated.

Other notes: Flowkooler 1751 water pump was just added and a new thermostat.


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post #2 of 38 Old 08-10-2020, 07:18 PM
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Sounds like non condensables in the system. Air in the system usually shows up in the high side. And you will see the pressure creep up as it runs. I see no mention of the system being evacuated, before it was charged.
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post #3 of 38 Old 08-10-2020, 07:57 PM Thread Starter
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Sorry thought I mentioned it. System was pulled down to 28 in hg before recharging each time. It held a vacuum overnight also.

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post #4 of 38 Old 08-10-2020, 08:48 PM
wranglertec
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High head pressure and over heating with the a/c on sounds like an air flow issue across the condenser and radiator. 1) if you have the electric fan behind the radiator make sure it is working. 2) if you have a fan and fan clutch make sure it is working. . I put my hand behind the fan out of harms way with the engine running with a/c on you should have air blowing on your hand.
3) if you have the hydraulic fan run off the power steering system the fan speed should go up with the a/c on or in high temp.


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post #5 of 38 Old 08-10-2020, 09:41 PM
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There are multiple things that could drive head pressure up:
Not enough air flow across the condenser
Dirty condenser or radiator
Non-condensables in the system
Bad compressor
Wrong refrigerant
Wrong orifice
Overcharge
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post #6 of 38 Old 08-10-2020, 09:46 PM
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Another question comes to mind:
Was the new condenser coil the same as the old one? Same area size, same number of rows?
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post #7 of 38 Old 08-11-2020, 04:57 AM Thread Starter
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Thank you all for the feedback.

I will evacuate and vacuum down again. There may be a possibility I put some air in, by not purging the middle line on the gauge set first. Not sure if that small volume of air would cause this.


The fan and fan relay are new. This has the electric and mechanical fan on it. Both work and the electric fan is one and blowing toward the engine. It sucks a piece of paper against the condenser and I can feel the airflow by the engine. Also, I tired a box fan blowing at the condenser also to see if that helped the pressures and it did not.


I am not sure about the condenser. I will look at the area and rows as you mentioned between the two. The condenser is making a 30 degree drop from inlet to outlet.


I weighed the refrigerant when I put it in and was able to put the recommended 24oz in.

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post #8 of 38 Old 08-11-2020, 01:37 PM
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Not sure about the high pressure on the a/c line.
I'm wondering about the cooling system though. I know the radiator was swapped in Spring but that's where I'd be looking.
On my '00 when towing a super heavy boat on the highway, a/c on, I would overheat the engine.

I could bring the temp back down by running the heat full blast. New rad solved it.

Try this.... make it begin to overheat again, leave the A/C on and run the heat. If it begins to cool back down, it's a radiator circulation issue and a radiator swap will fix it.
While you may not have something heavy to tow on the highway, maybe you can tow something else that puts some strain on the engine to replicate?

Probably a good idea to do the wp and t-stat too since that area will be a little easier to access. The all-aluminum unit from ebay is a popular upgrade and will fit your '00 nicely. Plenty of write ups on it available. It comes with a new cap too.

Another thought now that I'm remembering my '00... on the 99-'01 WJ there are these air diverters on the sides of the radiator that force oncoming air through the radiator/condenser instead of around it. If the radiator was swapped, those diverters were probably crumbling from time and, understandably, may not have been put back on. They're important. I saw where one owner made a set from some flexible plastic and cured a continuing overheat issue after a rad swap.

One other note....the temp "above the middle mark" isn't so unusual really, especially in higher elevations, like 3500+. Your location says you are only a little over 1000 ft but if higher is where you are, a little over half is normal given Summertime. Now if it keeps climbing...that's what I was seeing when I found the coolant circulation issue and that's a concern. If it goes there and stays, other then the odd a/c line pressure, I think you're good.

'04 Freedom Edition HO & '04 Overland HO (previous '00 Laredo 4.7)
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post #9 of 38 Old 08-12-2020, 11:56 AM Thread Starter
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Quote:
Originally Posted by Double E View Post
Not sure about the high pressure on the a/c line.
I'm wondering about the cooling system though. I know the radiator was swapped in Spring but that's where I'd be looking.
On my '00 when towing a super heavy boat on the highway, a/c on, I would overheat the engine.

I could bring the temp back down by running the heat full blast. New rad solved it.

Try this.... make it begin to overheat again, leave the A/C on and run the heat. If it begins to cool back down, it's a radiator circulation issue and a radiator swap will fix it.
While you may not have something heavy to tow on the highway, maybe you can tow something else that puts some strain on the engine to replicate?

Probably a good idea to do the wp and t-stat too since that area will be a little easier to access. The all-aluminum unit from ebay is a popular upgrade and will fit your '00 nicely. Plenty of write ups on it available. It comes with a new cap too.

Another thought now that I'm remembering my '00... on the 99-'01 WJ there are these air diverters on the sides of the radiator that force oncoming air through the radiator/condenser instead of around it. If the radiator was swapped, those diverters were probably crumbling from time and, understandably, may not have been put back on. They're important. I saw where one owner made a set from some flexible plastic and cured a continuing overheat issue after a rad swap.

One other note....the temp "above the middle mark" isn't so unusual really, especially in higher elevations, like 3500+. Your location says you are only a little over 1000 ft but if higher is where you are, a little over half is normal given Summertime. Now if it keeps climbing...that's what I was seeing when I found the coolant circulation issue and that's a concern. If it goes there and stays, other then the odd a/c line pressure, I think you're good.

Thanks for the feedback. I am wondering about the cooling system as well, but I have replaced every part in it.
-Radiator (rockauto), water pump (upgraded flowkooler model), thermostat (stant), and electric fan (rockauto


I have tried what you mentioned about getting it to overheat and then turning the AC to heat full blast, it does help, but it doesn't react fast, it takes some time and driving at speed to get it to cool the motor. It blows very hot air out then too. How quickly should the coolant temperature come down? I am almost at the point of buying a 180deg t-stat. I hear most people don't recommend this path, but if it helps keep it cool on hot summer days I would feel much better about it.


I know exactly what rubber air deflectors you are talking about because mine still has them and I was sure to transfer them over to the new radiator. I can't think the new radiator is that bad. The coolant looked good when I took I out also.


I am at 1000 ft. My question also is, the coolant temp sensor is right in the top to of the motor in the airflow path of the radiator. Is it possible this is giving a false high reading because the expended motor heat is blowing directly on it all the time? I wouldn't think so, but just a thought. Yes, mine keeps climbing to almost the next thick hash mark on the temp gauge past 210, which is why I changed the water pump and thermostat. I thought the pump might be slipping on the shaft, it was not, but put the new one in anyway.


Basically what you said is considered normal, just at tick past 210 and then never gets hotter. Mine keeps climbing with the AC on, with the AC off, it never really gets above 210. After you fixed your radiator, when towing the boat with A/C on did you ever have it overheat again?

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post #10 of 38 Old 08-12-2020, 03:58 PM
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The thermostat's main purpose is to allow the engine to warm up faster to minimize wear and tear on the engine. Changing it will not allow the engine to run cooler while driving.
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post #11 of 38 Old 08-12-2020, 08:32 PM
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I have seen several of these Jeeps with 20 year old mechanical fan clutches that barely work. You say you have replaced the electric fan, and it seems to be working well, but the mechanical fan and electric fan have to work in tandem to keep everything cool when its hot outside and the AC is running full blast. I replaced my fan clutch when i did the Ranger fan swap, and my cooling performance changed for the better dramatically. (I too, have changed the radiator and T-stat, and electric fan assembly also). I believe the fan clutch was my main problem, after the faulty electric fan that never came on, and that the Ranger blades just were a good add on the further keep things cool. I thought the mechanical fan was moving alot of air with the old clutch, but when i got the new one installed, i was impressed how much more air i was moving across that mechanical fan. A second Jeep in our mini fleet had the same overheating issues, and the Mechanical fan clutch was all we did to solve that problem. If the radiator is running hot, the AC condenser will be hot too, and thus the higher pressures. If the cooling system is operating properly, the fact that A/C is on or not should have no effect on the engine overheating. But the engine overheating will definitely effect AC operation. Just sayin....

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post #12 of 38 Old 08-13-2020, 09:21 AM Thread Starter
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Originally Posted by Bigrigr View Post
I have seen several of these Jeeps with 20 year old mechanical fan clutches that barely work. You say you have replaced the electric fan, and it seems to be working well, but the mechanical fan and electric fan have to work in tandem to keep everything cool when its hot outside and the AC is running full blast. I replaced my fan clutch when i did the Ranger fan swap, and my cooling performance changed for the better dramatically. (I too, have changed the radiator and T-stat, and electric fan assembly also). I believe the fan clutch was my main problem, after the faulty electric fan that never came on, and that the Ranger blades just were a good add on the further keep things cool. I thought the mechanical fan was moving alot of air with the old clutch, but when i got the new one installed, i was impressed how much more air i was moving across that mechanical fan. A second Jeep in our mini fleet had the same overheating issues, and the Mechanical fan clutch was all we did to solve that problem. If the radiator is running hot, the AC condenser will be hot too, and thus the higher pressures. If the cooling system is operating properly, the fact that A/C is on or not should have no effect on the engine overheating. But the engine overheating will definitely effect AC operation. Just sayin....
Thanks, you bring up a good point. I was wondering this myself. When the engine is hot and the electric fan kicks on, the mechanical one doesn't spin anymore. The airflow from the electric one stops it from spinning. I wasn't sure if this was by design, but after you mention this problem. Do you remember if it should spin when the engine is at 210 and the electric fan is on? I am assuming yes.

I looked up this ranger blade swap, might do that as well when I am in there.
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post #13 of 38 Old 08-13-2020, 09:28 AM
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That mechanical clutch is JUNK! It should never STOP spinning completely. Swap in the new clutch and Ranger fan and you will be SO glad you did.

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post #14 of 38 Old 08-13-2020, 12:54 PM
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Agree the temp continuing to climb with a/c needs to be resolved.
I'm square on the fan clutch as the most logical item to swap out. On my 2000, that was done early in the process to find my overheat cause.
The dealer recommended it before going straight to the radiator as I should have done myself. Hindsight tells me they already knew the fan clutch was a common culprit at just 4 years of use when this all occurred around 2004-5.

To answer the prior question, after I swapped the radiator, it never overheated again under any condition but my fan clutch was also new and lasted for 12 more years. Probably still has it on somewhere out there under different ownership.

'04 Freedom Edition HO & '04 Overland HO (previous '00 Laredo 4.7)
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post #15 of 38 Old 08-13-2020, 07:53 PM Thread Starter
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Thanks for the help on the cooling guys. I appreciate the help. I swapped the clutch and it spins all the time when hot now. Drove it around a bit tonight with the AC on and it didn't get hot until I stopped and run it at idle. Went to check the AC pressures again and the temp one hash past the middle line at idle. Is this typical of a 4.7L?

I am going to upgrade to the ranger fan in the near future, but wanted to make sure everything is normal before so I am not covering up an issue.

I will check the AC pressures again tomorrow when its hotter outside.
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