Compression Ignition Addict
Join Date: May 2013
Location: Yeah Right
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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 02:14 PM.