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post #4 of (permalink) Old 04-17-2002, 10:18 PM
dschwab9
 
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Re: R-134A retrofit

Those kits, if used the way they are marketed to be used (put it in and go) it's Bye Bye compressor in no time flat. 134a retrofits must be properly done to achieve good performance and insure that the system lasts.
I'm a certified tech and have done quite a few 134a retrofits. Here's a brief rundown of what you have to do to do it right:

You need to:
-First off, the refrigerent doens't just disapear. If it's low or empty, you have a leak that must be fixed.

-Pull the compressor and pour out as much oil as you can. Refill with the proper amount of POE oil (don't use PAG on a retrofit, it's incompatible with the residual mineral oil left in the system.

-Disconnect all the connections, and flush each component except the compressor with either mineral spirits or AC fushing solvent available at the parts store or a refrigeration supply house. The removes all the old mineral oil from the system. The retrofit will not work properly if the new oil/refrigerent is simply DO NOT flush the compressor.

-Pour proper amount of new oil in the suction port of the compressor and reinstall. One the hoses are connected, rotate the compressor by hand several times to make sure you don't have a cylinder full of oil when it starts up.

-Reassemble connections with new, 134a compatible, O-rings (either the green ones or blue ones - the green ones are better) If the system uses an orifice tube type metering device, replace it. It's probably partially clogged, and they're less than $3. If you have a TXV, it should be OK to reuse it.

-Replace the filter/dryer. THIS IS A MUST. Some of the materials used in older dryers for R-12 are not compatible with 134a and the synthetic oil it requires.

-Install service port adapters. Big one with Red cap on the high side, and little one with blue cap on the suction side.

-Vacuum down system for at least 30 minutes. The Air operated vacuum thingies really don't cut it. You need a real vacuum pump to insure the all the air/moisture is removed from the system.

-Put in one can of refrigerant and start the system with blower on high. Charge to aproximately 75% to 80% of the R12 capacity (if it took 50oz of R-12, use about 40oz of 134a). From here, you'll need to fine tune the system. You'll want to slowly add freon until compressor cycling slows and suction pressure is at 30-35 psi. This puts the evaporator temp just above the freezing point. High side my be as high as 350 psi in really hot weather, but try not to let it get much above that. If you have a site glass, you'll want to just barely clear it. There may be a few small bubbles present. Every system is just a little different. These guildlines should get you pretty close to the proper charge, but you'll have to "play with it" a little to get it perfect. Start with what I've said above, and then slowly adjust the charge while monitoring the vent temp until the coldest temp is achieved.

Make sure you use a proper guage set. You want come anywhere close to getting it right with that little "suicide hose" that comes with the kit.

-And above all else, Please be carefull. There have been people killed by attaching a refrigerent can to the high side. Liquid refrigerant can, and will give you frostbite, so be carefull when connecting/disconnecting service hoses.

Hope this helps you out man. If you have any more questions, please feel free to drop me an email.
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