# AC doesn't work



## mastermike (Jun 16, 2012)

The old R12 system in my 89 240 has stopped working. I want to change the system over to the 134A. What do i need to get from the parts store to do this? Are there any DIY threads on here to help me through the process? I want to here from all you guys out there that have changed from R12 to the 134A. Thanks, mike


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## smj999smj (Jan 1, 2006)

First, the old freon will need to be recovered from the system, if there is any. If you want to do it the right way, you would need to remove all of the old oil out of the system. This would mean removing the compressor, draining out the old oil and measuring the ammount, and replacing it with Ester oil that comes with the retrofit kit. The receiver/drier, which is the filter of the system, should be replaced as the desicant bag in the old one will deteriorate in time as it is not compatable with the new freon and oil. New receiver/driers are co-compatable with R-12 and R-134a. Next, a step a lot of people don't do: the evaporator would need to be removed (because of the expansion valve) and the lines should be flushed with the proper solvent and dried with compressed air. You can get away without doing this, but it is the only way to get all of the old oil out of the system. New "O" rings that come with the kit should be installed at any connection that was opened, ie the lines to the compressor. One ounce of Ester oil should be installed in the receiver/drier prior to installing it and an ounce added to the condensor, if that way flushed out. If you completely cleaned out all of the oil out of the system, including the evaporator, you should add another two ounces of Ester oil to the evaporator prior to reinstalling it. Next, the R-134a fittings should be installed; the valve cores of the R-12 fittings need to be removed prior to installing most of the new, R-134a conversion fittings. Next, to remove any moisture out of the system, it will need to be hooked up to an AC machine or vacuum pump to put the system under 30" of vacuum for at least 30 minutes. This will boil any moisture out of the system, which is important because any water in the system will mix with the freon and turn to acid. After this, the system should hold the vacuum if there are no leaks. If it doesn't, you will need to find the leak(s) and repair them. It's not a bad idea to install a dye in the system when charging it. Next, the system has to be recharged. This can be tricky to figure out how much freon to install; generally, the ammount of R-134a freon to install should be only 80-90% of the original system's R-12 capacity. This is where experience comes into play, as some systems will work better at the lower end of this range (80% charge) and some will require a little more to give the best AC performance. I usually start with an 80% charge and follow the AC performance test outlined in the factory service manual. By reading the high and low side gauges, taking in to consideration the ambient temperature and humidity, and reading the outlet temperature with a thermometer, I can add a little freon, if needed, up to the 90% charge, to get the system in an acceptable range. A lot of people do short cuts, not removing the compressor and draining out the oil nor flushing the system; some won't even replace the receiver/drier. All some will do is install the new fittings, put it under a vacuum and install the new freon. This will work for a while, but isn't the correct way. At the very least, replace the receiver/dryer . But, if you plan on keeping your Nissan for a long time, it'll pay in the long run to do it correctly. There are a number of sites on the web that explain the conversion; a simple Google-search should yield a number of hits. Good luck!


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## mastermike (Jun 16, 2012)

smj999, Thanks for the tips. I Like to do the job right the first time. Judging from your detailed reply it seems that you are too. I will follow your instruction to the T. AC should be cold as ice come Monday. Thanks again. Mike


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