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AC Charging problems High pressures no cooling
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RX7
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Jul 22, 2010, 9:03 AM
Post #1 of 6
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AC Charging problems High pressures no cooling
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97 Dodge Caravan, 3.0L, 150k
AC is not cooling. Purged and Evacuated the system, vacume held. After serviceing all worked ok. 2 hours later, again no cooling. Reconnected gages and found high pressures on both sides when the engine on and compressor running. Enguine off pressures on both sides were equal. During reserviceing pressures climbed to 350 on the high side and 80 on the low before engine was shut off and pressures bleed off. Changed front expansion valve, and reserviced, still no cooling and a repeat of the climbing pressures. Low pressure line did not cool as coolant was added. any ideas as to why the high pressures, and no cooling? Also why it would work once then quit. Could this indicate a blocked line, compressor, or rear expansion valve related problems?
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Hammer Time
Ultimate Carjunky
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Jul 22, 2010, 10:36 AM
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Re: AC Charging problems High pressures no cooling
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What you should be looking at is the cooling fan operation. It has a 2 speed system so make sure high speed is working on the cooling fans.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Jul 22, 2010, 2:54 PM
Post #3 of 6
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Re: AC Charging problems High pressures no cooling
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Fans must be correct as Hammer said. That and exact weight of charge must be known and on the target. Should be listed underhood on a sticker or I can look it up if none exists.
This would also be classic for overcharged which wont cool for crap either. It needs to be just right. Take pressures with just front system on (my suggestion) as both can confuse pressures as they fight for the condensed charge.
While filling you can't tell too much by feeling temps of lines as just the transfer isn't dependable till you stop and let it run. The exact weight of charge is critical. Too low or too high wont cool well or at all. If you didn't weight in the charge especially with dual system it's like target practice with a blindfold,
T
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Hammer Time
Ultimate Carjunky
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Jul 22, 2010, 2:58 PM
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Re: AC Charging problems High pressures no cooling
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As I said, this one uses a 2 speed fan so you can have no idea how much refrigerant is in it judging by the pressures because once the second speed kicks, all the pressures drop again. As Tom said, you need to weigh the charge to know exactly how much is in there. Just judging by your description, I suspect you have a fan problem.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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RX7
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Jul 22, 2010, 9:12 PM
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Re: AC Charging problems High pressures no cooling
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To hammer and Tom, thanks for the quick response and inputs. I will give them a try tomorrow. I could not find a specification or wt chart for the amount of 134 and oil needed. Can one of you provide the data or a site linkfor me or should I call the parts house or dealership?
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Tom Greenleaf
Ultimate Carjunky
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Jul 22, 2010, 11:39 PM
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Re:97 Caravan, dual AC Charging problems High pressures no cooling
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Capacities from empty show 1996-2003 Dodge Caravan w/Front & Rear A/C 46 ounces of R-134a and 13 ounces pf PAG-46 oil for system total - all engines used the same charge amounts.
Two different charts showed that but both always say to go by any underhood information. Remember, only small amounts of oil come out when evacuating for a charge if a leak was fixed or a part replaced that emptied system. You calculate how much oil was lost unless starting from known empty of oil or by draining the part removed and measure what you got out plus a couple for this capacity depending on circumstances. Oil amounts for repairs is educated guessing.
Too much oil will cause erratic pressures and uneven cooling up to choking the compressor and too little will underlube compressor for early failure.
You weigh in the charge by taking tare weight of whatever set up you are using and containers and deducting till you have this as close to the ounce as you can. This large a capacity system would tolerate being off a couple ounces of refrigerant - to some that's a big %.
When both pressures are high it can mean temps are too high or too much refrigerant usually. You can try spraying condenser with mist of water and watch pressures drop. There is a very distinct and accurate relationship of temps and pressures for refrigerants. Air must never be allowed into the system and even purging hoses of gauge set or any unknown sealed equipment must be purged first.
There's plenty of moisture in air which can cause very erratic reading, icing in spots inside unseen at places of expansion, X valve or a restriction.
Note: use pure refrigerant with no additives except for UV dyes when desired that is available in small cans that can be run thru real gauge set with a can tap and long hose helps for weighing. Postage scales can be used for small cans or any scale that can break down to ounces if using larger container. Machines can count how many ounces have been delivered not something the average person wants to buy.
What was the repair or reason for the work at all? Most reasons are to fix a leak. Anything that contains refrigerant can leak. Service ports, O rings, compressor seals, hoses, condenser, expansion valves, evaporator(s) switches that sense temp or pressures - anything that is sealing in the charge.
Vacuum: At sea level vacuum is 29.92 Hg (inches of mercury) and you can deduct 1 Hg for each 1,000 ft. of elevation. It must hold a vacuum or you wouldn't expect it hold pressures.
I've seen calculations of loss of charge per year that is normal but it's not dependable IMO. I've seen some untouched and fine over 15 years and some that need tweaking after a few years,
T
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