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Old 04-26-2011, 08:27 PM   #1
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Question Does bypassing the low pressure cycling switch fix a problem, or put a band-aid on 1?

BLUF: A/C Clutch not kicking on. Air temp is same as outside air.
My Story:I live in the south, and when it started to warm up I noticed that my air wasn't getting cold after not being used over the winter. So, I take my jeep to Firestone for a diagnostic. They told me that the system was full of Freon, and no leaks were found. Also, they were reading error code P0645 (Air Conditioning Clutch Relay Circuit Malfunction). Firestone said that they could not fix this issue, and recommended I take it to the dealer.
Well after charging me to put a new compressor on, they find out that it's not the compressor, and it's the pressure switch.
By this time I'm furious (long story) with the "stealership". So I tell them not to do any more work on my jeep, vow to do all of my own work, and I get home and start scouring the web about A/C issues.

So today I disconnected and shorted the connector that plugs into the low pressure cycling switch. While shorted, the clutch kicks on, and A/C blows cold air. Does this mean the switch is bad, or is this a result of another issue? If replacing the switch doesn't fix the problem, will I damage the system by bypassing the switch?

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Old 04-26-2011, 09:09 PM   #2
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Well first welcome to the forum. Now what are the specifics of you jeep, year engine tranny? It will make it easier to help you along your way.

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Old 04-26-2011, 10:17 PM   #3
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'06 TJ, 4.0L, Automatic
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Old 04-26-2011, 11:18 PM   #4
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Alright now here is what I know the low pressure cycling switch locks up the clutch on the compressor intermittently when it senses that the freon level is low. It cycles the freon around to help keep the seals from drying out and causing a total loss of freon. If you bypass this switch the compressor will be permanently locked witch can cause the clutch to fail prematurely. So if you don't want to replace the compressor or the clutch again then replace the switch.
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Old 04-27-2011, 08:20 PM   #5
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in a nutshell that pressure switch controls the compressor it will energize the clutch until the low side pressure is pulled down to about 27 psi +or - the switch then opens and the compressor stops until the low side pressure increases to about 42 lbs if memory serves then repeats that seqence / a good indicator that your freon is low would be compressor cycling rapidly and bypassing that switch will destroy the compressor if you left it bypassed , its ok to do that to charge the system but not to run with/also some accumulators have shrader valves in them which would allow you to change that switch without draining the system down but i am not sure about jeep ones
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Old 04-28-2011, 11:28 PM   #6
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Thanks for the info. I'm gonna replace the switch as soon as I get a chance. I'll post the results once complete.
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Old 05-02-2011, 06:01 PM   #7
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Question

Power was finally restored to my house in Alabama. So I was finally able to return home after being displaced for five days, and my package was waiting at my door. I swapped out the switch at about 1130 am this morning, ran about 4 hours worth of errands, and the A/C has been blowing cold air the whole time .

Once the A/C started working, I connected a gauge to the low service port to measure the A/C pressure. The gauge is showing approx. 57 psi (85 degrees ambient), and the air doesn't seem to be as cold as I remember it being before.

Is there a SAFE way to let some of the pressure out? Or should I just be happy I have air, and leave it alone?

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a/c issues , cycling switch , low pressure switch , tj technical question

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