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Old 06-20-2012, 02:56 PM   #1
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AC Troubleshooting

I have a 99 TJ 4.0 and recently the AC decided to blow not so cold air. It's not exactly blowing hot but can't be cooler than 65 70 degrees. The compressor and clutch kick on every 5 seconds or so (is this normal to kick on so often?). I thought it might be low on freon so I went and purchased the quick charge kit. I hooked that up with the jeep running and ac on full and the gauge goes up to about 50-55 then the compressor kicks on and it shoots down to around 15. Once the compressor shuts off it goes back up to 50-55. I checked this as well with the jeep off and the pressure is up in the red zone where it's says that may indicate a hardware problem. I guess what I'm asking is where do I go from here? I live in PR so if I go to an AC shop I'm pretty confident they will tell me to replace the entire motor (kidding... kind of). Any insight would be greatly appreciated.

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Old 06-20-2012, 05:58 PM   #2
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Also, when I check the pressure with the jeep off it's at around 90. Does this indicate something specific?

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Old 06-20-2012, 06:01 PM   #3
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no its not normal to go on and off so often. It will go on and off based on pressure when running. it will run until your pressure drops below the low pressure cut off. then turn back on when the pressure equalizes..then go back on.. so on so on. Your system should hold around one and a quarter pounds, or .567 kilograms. If you ask me it sounds like your still low on freon. A running pressure of 15psi is below your pressure cut off. your running pressure should be around 40 to 45 psi. The pressure when your jeep is off doesnt matter. well not that it doesnt matter but not as important.
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Old 06-20-2012, 07:15 PM   #4
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That's where I'm confused. With the AC on full the line under the hood is very cold to the touch. With the refill can hooked up the pressure rises and drops as the compressor kicks in. With the clutch engaged the pressure drops pretty low but when it cycles off the pressure rises up into the red. Is that normal?
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Old 06-20-2012, 09:07 PM   #5
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Yes thats normal. I will try to explain. When your system is running one line is cold and another is warm/hot. The pressure in the cold line is different than the pressure in your warm/hot line. With the system off your pressures will equalize. The reason for the different pressures is there is a metering device is all a/c systems. The metering device (for lack of better words) slows down the freon to change it back to a liquid state. The pressure coming out of your compressor is higher than the pressure returning to your compressor.
One more quick example. Say your home a/c is running and has r-22 freon in it. Your low side pressure will be 68 lbs of pressure and your high side pressure will be 225 lbs. When the system is off it may be around 120 lbs pressure when equalized. Dont hold me to those numbers because there are other variables that could change pressures. But it was just an example. I hope that helps and didnt confuse you more.
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Old 06-20-2012, 09:15 PM   #6
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Thank you for the reply. I am just trying to avoid overcharging the system. Should I just watch the gauge and as its moving up and down just shoot for around 50 psi when the clutch is engaged? The ambient temp here will likely be around 90 which is why I say 50. Thanks again for the help.
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Old 06-21-2012, 05:16 AM   #7
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At 90*F, your low side pressure (where the port is) should be 45 - 55 psi. Mine was down at 30 psi and required several ounces of refrigerant.
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Old 06-21-2012, 06:11 PM   #8
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Once you add enough freon to get above the low pressure cut off, it will stay running. I would think 50psi would be a good # on a 90 degree day.
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Old 06-21-2012, 06:54 PM   #9
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If you need to add freon that means you have a leak...fix that first. Adding freon is just a temp fix and not a good one at that...eventually you'll have other issues from moisture and contaminants getting into your unsealed system. Putting in some dye and using a blacklight is the easiest way to find a leak. Once you find and fix the leak i'd bring it to a shop to have it properly evacuated and charged...or just bring it in and have them fix it.
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Old 08-23-2012, 07:27 PM   #10
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Just running through my old threads. The can of freon from wally's fixed it right up. Thanks for the replies.
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Old 08-23-2012, 08:45 PM   #11
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Quote:
Originally Posted by BLK01 View Post
The metering device (for lack of better words) slows down the freon to change it back to a liquid state.
the metering device is a term used because there are numerous types such as a fixed bore,capillary tube,TXV,EEV etc.

the metering device turns liquid refrigerant into a mist(like misting your face with a spray bottle) to increase the surface area of the refrigerant allowing more heat to be absorbed into the refrigerant. this action turns the liquid into a gas state. after it turns into a gas it is now allowed to return to the compressor(you cannot compress a liquid) and be compressed into a high pressure hot gas. when the refrigerant cycles through the condenser it desuperheats and subcools the refrigerant turning it back into a high pressure liquid. this liquid is sent through the metering device again and the cycle continues.

to the OP. your system is low on refrigerant and it has a leak. leak needs to be fixed.
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Old 08-23-2012, 09:12 PM   #12
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Thanks for the info. What do you suggest to find the leak? I'm in PR so immediately they see $$$$ when the gringo walks in. I'm comfortable doing most work myself do you think i have a chance?
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Old 08-23-2012, 10:01 PM   #13
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late 90's chryslers are known for leaky evaporator coils. i have a 1997 and replaced mine this past spring. i do HVAC for a living(can ya tell?) and i have all of the necessary tools and supplies to get the job done properly( gauges,nitrogen,vacuum pump etc.) i wish you lived closer so i could hook you up.

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