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Unread 04-10-2011, 03:00 PM   #1
srode
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1999 Grand Cherokee AC Problem

99 Grand Cherokee Laredo with 4.7 V8, 161,000 miles - No cold air - The compressor is cycling - running for a very short period of time and then off for longer - maybe 2 seconds on and 15 seconds off, no cold air and the low side line is not cold, the high side is hot. The electric fan is running behind the radiator, the belt driven fan is coasting turning slowly at idle. I don't drive it but the wife says hot air coming out the side vents and ambient air temp coming out the center vent. I'm thinking it might be low on Freon - the AC hasn't been serivced since new - we are the original owners. Its a manual system not automatic temperature control. I have a set of gauges but don't know what the high or low side should be & I don't know what kind of Freon is in it. Can anyone tell me typical high / low side pressures, freon type and where the cut off point for pressure is supposed to be on the high and low side to kick off the compressor? Any trouble shooting tips would be greatly appreciated too!

Thanks, Steve

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1999 Jeep Grand Cherokee 4x4 Quadra Drive 4.7 L 163,000 miles(sold)
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Unread 04-10-2011, 03:25 PM   #2
iluvtruenos
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r134a, sounds like it's low.

Hook up the low/high side gauges and see if it cycles.
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Unread 04-10-2011, 04:17 PM   #3
HVACNY
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If the compressor is short cycling its most likely low on gas.AC is a closed system,meaning if it worked correctly until this season then it has a leak.If its a slow leak then you can take it somewhere they can pressurize the system or put dye into the system to find the leak,fix the leak,evacuate and then charge it.Or you can keep filling it with gas and eventually kill your compressor.Its also against federal law to keep filling a system that has a known leak.People do that,i dont.The proper pressure depends on alot of factors like ambient temp,type of gas,restrictions in the system.Be carefull if you decide to diy.
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Unread 04-10-2011, 05:30 PM   #4
nickblack
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^^^ x 2, Please take it to a qualified shop if you are not sure what you are doing, can be very dangerous. Put a new set of a/c lines and a new accumulator/drier after 12 years of use. If DIY, make sure to pressure test the system and vacuum it out completely before refilling. I changed my compressor, all hoses, accumulator and Variable Orifice line 2 years ago and refilled with freon. I don't remember what the high/low pressures were, but I do know they vary according to ambient temperature.
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Unread 04-10-2011, 07:47 PM   #5
srode
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Is there a chart for pressures vs ambient for 134a Freon? I've worked on AC years ago when I was a mechanic, not recently.
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2008 XK Commander Limited 4.7 Quadra Trak II
1999 Jeep Grand Cherokee 4x4 Quadra Drive 4.7 L 163,000 miles(sold)
2004 GMC SLT Crew Cab 4x4 Duramax Diesel
1969 Camaro Pace Car
1969 Camaro Hard top
91 Cherokee - sold at 188,000 miles, still runing great at 250k last report
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Unread 04-10-2011, 10:22 PM   #6
wj0313
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A good High Side Pressure Reading for 134a = twice the ambient temperature + 50. For Example at 85 F, you would expect a high side pressure of 85x2=170+50 = 220 psig.
Low side should be around 30-35 lbs
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Unread 04-11-2011, 03:27 AM   #7
srode
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Thanks, that's what I need!
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2008 XK Commander Limited 4.7 Quadra Trak II
1999 Jeep Grand Cherokee 4x4 Quadra Drive 4.7 L 163,000 miles(sold)
2004 GMC SLT Crew Cab 4x4 Duramax Diesel
1969 Camaro Pace Car
1969 Camaro Hard top
91 Cherokee - sold at 188,000 miles, still runing great at 250k last report
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