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Old 07-10-2013, 05:26 PM
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A/C Issues

So it's 100 deg in Texas and my ac went out. I went to recharge it and noticed the cap for the high side port was missing, then I noticed a dent in the hood where I'm guessing the cap blew off. I went ahead and recharged the system and the air worked for a day then quit cooling again. I would say I have a leak and I'm hoping it is just the high side valve that failed. I have new valves, low and high, ordered and plan to replace. I was also going to borrow a set of gauges and check the pressures after I replace the valves. Two questions; what should the pressures read and does anyone think something else could be wrong other than just a valve failure?
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Old 07-22-2013, 08:09 PM
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A/C pressures vary too much to give a precise specification because of ambient air temperature and relative humidity. On a typical 75 degree day with LOW humidity, I would like to see my high side around 220-250PSI and the low side between 30-40PSI with the compressor ENGAGED. It's possible the valve failed, but not likely. You really should have it checked out by an A/C shop. Put too much refrigerant in it and you'll have even bigger problems!
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Old 07-23-2013, 04:07 AM
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Please correct me if I am wrong here but our A/C systems are closed loop which means theoretically, they should never need to be recharged.

A recharge event would be needed if the system has been opened due to a failed/replaced component or a leak. Both of which would require a good purge and cleansing of the system. Otherwise those quick fix A/C in a can systems will cause more harm then good allowing more contamination to enter the system.

May want to get some dye injected into the system then a UV light to search for the dye.

I'm not an expert though.
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Old 07-23-2013, 04:52 AM
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You are correct...they are closed. To an extent. The system uses R-134a. The molecules are so small that over time the system will deplete...usually a long time. I know, because I've had to diagnose that several times and it was a nightmare. But in his case, it quit cooling again rather quickly. Indeed, his system has a sizable leak or a failed component...either of which should be checked by someone who has knowledge of the A/C system.
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Old 07-23-2013, 09:18 AM
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Thanks for the help. I changed both the low side and high side schrader valves. System held a vacuum for 30 minutes with out pressure changing so I would say I fixed the leak. I recharged the system and pressures are 25 on the low side and 250 on the high side. I was concerned with something causing the high side pressure to spike and cause the valve to fail.
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Old 07-23-2013, 01:10 PM
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30 mins of a vacuum hold may or may not be adequate to diagnose a leak. I usually let it sit for a few hours. I just rebuilt the AC on two vehicles, each with their own slew of issues. Typically though, a good few drops of UV dye, a UV flashlight from Amazon, and some patience will make diagnosis fairly easy.

Walmart has the best price I've found on R134a. I usually buy one can of the cheap stuff (12oz) for diagnosis and two or three, depending of the system, of full synthetic. Vacuum out the system, throw in some dye and let it suck into the system with the R134a. Run it for a few minutes or go for a quick drive. Find the leak, replace the o-ring or part.

THEN, vacuum and let it sit for about two hours after a one hour purge. If the gauges stay put on BOTH sides (high and low), then I'd assume it's ready to replace the accumulator/drier if it's been exposed to the atmosphere more than an a half hour or so. This includes if the system has completely leaked out.

Good luck. Check your system's capacity and only fill to that level. I weigh cans while I fill on a scale. For instance, my little civic uses only 1.7 pounds of refrigerant. Easy to measure this with a scale. Better than the high and low pressure delta methods since those can be off significantly due to ambient temperature, air flow through the condensor, condition of the expansion valve, etc. Get a cheapo postage scale at Walmart/Target with at least 0.1 pound resolution. Grams are better if you feel like buying a nice one.

Last edited by Expirobo; 07-23-2013 at 01:14 PM.
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