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 Post subject: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 3:53 pm 
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Hi all,

Just noticed that at current temperatures around 50F (10C) my AC compressor clutch is cycling on and off for like 2-3 seconds per cycle at idle. AC itself is off, heat is directed to my feet, not onto the windshield. Is it intended or is it a sign of a problem?

Thanks in advance,
A.

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 4:40 pm 
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Definite "maybe"

Per 06 Owner's Manual pg 209 the AC compressor will cycle with the AC switch off and vent mode set to floor and temp control set to heat. This is in order to keep moisture from building up inside the vehicle and fogging the windows. All "modern" vehicles with AC do this or something similar.

That said the compressor should not IMHO be tripping on/off every 2-3 seconds. Only reason I can think for it to do that is low freon or perhaps a bad freon pressure switch. IIRC there is a easy to swap out pressure switch that might be the cause but I'll defer on where to others that know more than I.

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 8:03 pm 
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All CRD's are designed to cycle the AC to keep the refrigerant (which is also a lubricant) flowing through the system. It prevents the internal seals from dry rotting and leaking. I don't remember which settings they are, but there are only a few that DO NOT cycle the AC like you're witnessing. There is a modification to the switch assembly that will prevent this behavior, but it requires soldering a few jumpers into the switch and cutting a few copper connections out of it. Not difficult, but also not everyones idea of Saturday night fun. The AC switching on and off so frequently almost certainly costs the vehicle a small amount of power, and therefore mileage, but how much I do not know. You may be best to research the settings that avoid it and be mindful to flip the AC on every once in awhile to lubricate it.

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 9:48 pm 
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AC compressor cycles with low refrigerant pressure or malfunctioning high pressure sensor (the one located on passenger side on what seems to be the filter). Check cables, try to re-seat the plug, or measure the voltage coming out from that sensor. Also check charge. Yes, it cycles even with AC off.

Not sure if pressure can be affected by low ambient temps... Here we don't go below 18C :mrgreen:

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 10:21 pm 
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AC compressor cycling on and off is a sure sign of low freon levels in the system. When the low pressure side of the system as measured by the low pressure switch sees the pressure too low, it will cut off the compressor off to protect it since the freon lubricates the compressors internalls.

As others have stated, you can modify the rotary control switch so the AC compressor is only engaged in the AC Cool position.
This is the picture showing the required modifications:
I have done the mod to my CRD several years back and it works just fine!

Image

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Thu Jan 11, 2018 10:31 pm 
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WWDiesel wrote:
When the low pressure side of the system as measured by the low pressure switch sees the pressure too low, it will cut off the compressor off.


Hi WWDiesel, just for my benefit, which is the low pressure side and high pressure side on CRD's system?

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Fri Jan 12, 2018 12:22 am 
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Wow, thanks! During the summer my AC worked just fine, which of course doesn't mean that freon level is normal. Given the vehicle age some freon loss is inevitable. BTW, I verified that this behavior is blow switch position dependent. If I switch the air into my face, this stops. This is in line with the info from papadingo.

WWDiesel: thanks so much for the info and the drawing! I presume pictured are the innards of the cabin air blow redirection switch, correct?

Anything peculiar about adding freon to CRD? I am starting to suspect that on our vehicle any essential procedure requires either radical engine disassembly or even a surgery with reciprocating saw:)

Thanks again!
Alex

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Fri Jan 12, 2018 1:46 pm 
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BoarX wrote:
WWDiesel: thanks so much for the info and the drawing! I presume pictured are the innards of the cabin air blow redirection switch, correct?
Anything peculiar about adding freon to CRD? I am starting to suspect that on our vehicle any essential procedure requires either radical engine disassembly or even a surgery with reciprocating saw:)
Thanks again!
Alex

Quote:
I presume pictured are the innards of the cabin air blow redirection switch, correct?

Yes, that is correct, it is the backside of the HVAC control switch!

As to adding freon: Best method is to have an AC shop remove all the freon, measure the amount and then replenish with the correct amount required for the system. Doing this also runs all the removed freon through a special filter to remove any foreign material.
Freon can be added to the low pressure suction side, but you must have gauges and be very experienced in reading them and knowing what the correct pressure requirements and limitations are based on the ambient air temperature passing through the condenser. If you don't have gauges and experience in using them, it is best left to a shop with the correct equipment and trained technicians....

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05 Jeep Liberty CRD Limited :JEEPIN:
Blk Brush Guard/Hella's/LED's
Ironman Springs/Bilstein's
Yeti Stg4 MaxTune
Weeks ElbowKit/Battery Tray
NO FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pump
2mic.Sec.Fuel Filter
Flowmaster/NOcat
V6 Airbox
GM11 blade fan/Hayden HD clutch
Ironrock Trilink
98 Dodge Cummins, 5"exh. Viair,K&N


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 Post subject: Re: AC compressor cycling at idle
PostPosted: Mon Jan 15, 2018 9:51 pm 
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Thinking further I am wondering if the observed intermittent AC compressor clutch engagement could be a result of the removed mechanical fan and several pieces of cardboard covering the radiator/intercooler/AC_condenser pack? The other day I noticed electrical fan switching on while the engine was still idling, slowly warming up. Maybe condenser still needs some mechanical fan action after all?

Curious,
A.

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 Post subject: Re: AC compressor cycling at idle
PostPosted: Mon Jan 15, 2018 10:27 pm 
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The electric fan will turn on when the AC turns on.

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