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Old 03-17-2011, 04:22 PM   #1
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Default A/C To Cold, Compressor Won't Cycle Off

I am going to try and include all relevant information, but I am sure I will forget something. 97 XJ. I noticed a issue with H2O leaking into the floor, checked the drain and it is clear. I realized that the evaporator was freezing up, A/C wouldn't blow as hard as normal, and when it would thaw I would have the leak. The A/C blows super cold, I can't run it with the temp selector all the way to the left or on MAX. It even blows cold with the selector pointed in the middle position. I realized today the the compressor will not cycle off. When the mode switch is in a position the the compressor should be on the compressor and all related components come on, the compressor stays on till the switch is moved to a different position. Could it be one of the pressure sensors ? If it is can the sensor be removed and replaced without loosing all my freon? Thanks for any help, and when I get this figured out I will hit you up with another issue ( cruise and A/C on, when I hit a hill the A/C blows out defrost/inside the dash, and cruise stays on. Cant find vacuum leak under the hood anywhere) First things first.

Last edited by michael_jnel; 03-17-2011 at 04:38 PM.
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Old 03-18-2011, 07:25 AM   #2
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Anyone???
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Old 03-18-2011, 08:20 AM   #3
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I have two thoughts...one, is that the fins are plugged up not allowing proper air flow (Dodge truck had this problem). Second, is the compressor is going out or low on freon. When the valves wear out they don't maintain correct monitoring...hence the freezing up. I have had this problem on my walk in cooler, recharge it and works for a few more months. I am not very efficient with AC but I tried giving you ideas
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Old 03-18-2011, 09:53 AM   #4
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Take it to a pro, they'll install the gauges checking low/high pressure. If u Google a/c freeze-up, u'll find all kinds of reasons - dirt, blockage, etc.
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Old 03-18-2011, 10:13 AM   #5
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#1 cause of evaporator freeze up in any mobile A/C system (not just jeeps) is poor air flow through the evaporator, running the blower on low with the temp selector on the coldest setting will cause this.

Another possable cause (I don't even know if Jeeps have this) is the thermostatic switch that cuts the compressor on and off based on the temperature of the evap. core is faulty. I usually se them go the other way though, they won't cycle the compresser on.

A third cause could be your low and/or high pressure switch's are not working right and allowing the compressor to keep running. When the evap. core is froze usually the high side pressure starts to rise because of the restricted air flow, and eventually the compressor shuts off untill pressure returns to a safe level.

First thing I would do is run the blower on 3 or 4 and back the temp selector down a bit see if that helps. You also might need to remove the evap/heater core and clean it. The fins could be clogged and not letting enough air flow through, even though you can feel it blowing air, dosen't mean it's clean.

Last edited by ww2farmer; 03-18-2011 at 10:14 AM. Reason: spelling
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Old 03-18-2011, 12:00 PM   #6
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With the compressor staying running I would think that the pressure switch would be most likely. How hard is it to get to the evaporator core? It looks like a pain. If I remove the pressure switch will I lose all my freon?
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Old 03-18-2011, 12:48 PM   #7
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Quote:
Originally Posted by michael_jnel View Post
With the compressor staying running I would think that the pressure switch would be most likely. How hard is it to get to the evaporator core? It looks like a pain. If I remove the pressure switch will I lose all my freon?
Some pressure switch fittings have valves that close when the switch is unscrewed from the fitting so the gas won't escape. I don't know if a Jeep does or not, never had to change one. Most of the evaporators I deal with in my work are located where the heater core is, often times they are one unit. I have yet to see a car/truck/tractor or any thing on wheels where the heatercore/evap is not, at the least, a minor p.i.t.a. to get to, and often times requires a 3rd arm and the ability to stand on your head.
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Old 03-18-2011, 03:31 PM   #8
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Quote:
Originally Posted by ww2farmer View Post
Some pressure switch fittings have valves that close when the switch is unscrewed from the fitting so the gas won't escape. I don't know if a Jeep does or not, never had to change one. Most of the evaporators I deal with in my work are located where the heater core is, often times they are one unit. I have yet to see a car/truck/tractor or any thing on wheels where the heatercore/evap is not, at the least, a minor p.i.t.a. to get to, and often times requires a 3rd arm and the ability to stand on your head.
I figured that getting to the evaporator would be a mess. UGH!!!
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Old 03-18-2011, 03:39 PM   #9
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It could be as simple as the A/C relay being stuck. Swap the relay and see if there is a change.
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Old 03-18-2011, 04:23 PM   #10
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I just swapped the relay with the ABS and the same thing. I tried this also, I removed the low pressure switch from the line and plugged the connector in, the compressor wouldn't come on. Reinstalled it and compressor stayed on like before. I removed the high side switch and plugged it back in and the compressor stayed running like before. Also, how hot should the line on the high side be? I couldn't keep my finger on it for more than a second?
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Old 03-18-2011, 05:05 PM   #11
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faulty high side pressure sensor, it's the one on the back of the compressor in the lines set head, low side switch is on the drier located on the passenger side firewall
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Old 03-18-2011, 06:44 PM   #12
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Quote:
Originally Posted by michael_jnel View Post
I just swapped the relay with the ABS and the same thing. I tried this also, I removed the low pressure switch from the line and plugged the connector in, the compressor wouldn't come on. Reinstalled it and compressor stayed on like before. I removed the high side switch and plugged it back in and the compressor stayed running like before. Also, how hot should the line on the high side be? I couldn't keep my finger on it for more than a second?
It's some what normal in a 134a system for the high pressure line off the compressor to the condenser to be very warm/border line hot, the receiver dryer should also feel warm, but not hot. If the receiver dryer is hot it usualy indicates poor air flow through the condenser, and/or a partialy blocked expansion valve. 90% of the time I encounter a plugged condenser causeing excesive heat at the rec. dryer, and poor cooling.
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Old 03-24-2011, 05:35 PM   #13
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It was the high pressure switch that was the problem. Thanks for the help guys. Now time to track down the impossible to find vacuum leak.
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Old 03-24-2011, 05:35 PM
 
 
 
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