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Architecture & Porsche's
Join Date: Jan 2006
Location: Austin, Texas
Posts: 3,189
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Odd AC question: gauges wildly fluctuation with R12 charge...experts??
Ok, my 951S has a very cold AC, but since I've purchased the car, I've noticed that it either blows very cold or cool, & ocillates back & forth about ever 10 seconds or so.
The inside of the car is cold, but if you feel the vents you can feel the temperature variations on a 10-15 second cycle. Lately, I've been talking on the phone with the radio off & now notice a relay "trip" sound coming from the fuse box (area) when this happens. As well, I can feel the AC compressor cycle on/off when this happens as the engine's power changes slightly. On the gauges today at the body shop, We'd see the low-pressure gauge increase up to 45psi (within 10-15 seconds), and then immediately bump down to 15psi, then creep up again to 45ps within 10-15 seconds. On the high-pressure gauge, it sits low (150 and once the low pressure falls to 15psi, the high pressure goes up to 215, but starts falling back down to 150, all within the same 10-15 seconds. I think I have this right: one gauge is rising, the other is falling. All I can think of is that a high press or low press switch is bad: thoughts??? Mark
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Porsche Club Racing National Scrutineer '89 Andial 951 '82 928R '74 911 RSR 3.6 |
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05-05-2009, 01:26 PM
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Just thinking out loud
Join Date: Nov 2001
Location: Close by
Posts: 6,885
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That sounds normal when you are low on freon. Unfortunately, you have a leak. If you haven't gotten it sorted by May 17th, let me know. I'm coming to Austin for a few days to do some a/c work. I can get R12.
Depending on the ambient temps, your low should be around 27-30, and the high should stay below 250 when the compressor is running. The high side is more dependent on the ambient temperature, and how much air flow you get across the condenser.
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83 944 91 FJ80 84 Ram Charger (now gone) Last edited by mattdavis11; 05-05-2009 at 03:05 PM.. |
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05-05-2009, 03:01 PM
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Architecture & Porsche's
Join Date: Jan 2006
Location: Austin, Texas
Posts: 3,189
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I just got the car back, it was low on freon, however, the system has not been serviced in 6 years and the caps were good: plus, I've had the car for 9 months & it's been this way ever since I got it, starting to wonder if it was under-charged in the first place.
Blows colder, which is hard to imagine, however my intermittent relay "trip" and such continues...wierd. More than likely, the gauges are working like they were before as well. I had 3/4lb of freon, they added 1.25, so I have 2.0lbs now. Mark
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Porsche Club Racing National Scrutineer '89 Andial 951 '82 928R '74 911 RSR 3.6 |
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05-05-2009, 03:03 PM
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Just thinking out loud
Join Date: Nov 2001
Location: Close by
Posts: 6,885
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2.09lbs is the capacity. I hope they changed the schrader valves. It's the most common source for a leak on any a/c system. Sometimes they will only leak down to a certain pressure. Same thing as a bike tire, it won't stay full, but it won't go completely flat either.
Everybody's a/c is supposed to cycle, the gauges are acting normal. It won't cycle as often when it gets hotter, and it won't feel as cold either. The reason is there will be less heat transfered away from compressed freon in the condenser when the ambient temperature become 95 degrees, which will be pretty soon. It's really nice when it's 75 out, it cools the freon very well. Clean your condenser with some simple green, it's easy to do, and will keep the high side pressures down = better cooling.
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83 944 91 FJ80 84 Ram Charger (now gone) |
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05-05-2009, 03:15 PM
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