Posted by Jon Hagen on July 27, 2015 at 14:09:48 from (69.26.23.81):
In Reply to: Re: Pickup AC Repair posted by dhermesc on July 27, 2015 at 12:56:28:
Can you really convert from R12 to R134a with only the Walmart / Interdynamics $45 retrofit kit ?? The answer is sometimes yes. The Walmart kit contains the R134a conversion fittings, a can of 8.5 oz of ester oil and refrigerant, plus another 2-3 cans of R134a, and a tapper / charging hose.
They tell you to vac the system, add the 8.5 oz of oil charge on top of what remaining mineral oil is in the system, then add enough extra R134 until it is cooling good.
Just to satisfy my own curosity, I converted my old 79 Dodge full size van using one of the interdynamics kits, I knew the system was working and only low on R12, so I experimented , doing it the way interdynamics said. Only thing I added was to vacuum the system for 2 hours to get the old dryer as dry as possible.
The conversion worked well, being done on an otherwise good working system. It cooled well and would only leak a few oz per year, I ran it that way for near 10 years.
If the system has had a compressor fail and the system is full of metal trash, you MUST flush the system and replace the dryer along with the compressor if you want it to work / last.
Back in the day when the big change from R12 to R134a was the deal I followed a couple of AC repair sites where guys who did AC for a living, soon found out what would work and what would not, and shared that with us shade tree AC guys.
What had everyone in an uproar, was that originally they said you had to change almost everything to do a successful R12 to R134a conversion, big bucks. Had to change compressor, dryer, all hoses, and condenser. After about a year of trying, the AC guys found it was not really that bad. In most cases, your old compressor, hoses, condenser and expansion valve would do just fine.
The old R12 hoses, if in good condition, would work fine, as years of mineral oil running through them made a pretty effective seal that leaked very little R134a. For that reason, many recommended NOT flushing unless a compressor had failed, as the flush removed some of that mineral oil stop leak coating. It turns out that on an otherwise good AC system, the shade tre mechanic could do a reliable R12 to R134a conversion for a bout $100 in parts and his own labor IF he had his own basic AC tools like a vac pump, gauge set and vent thermometer. A parts store " Fix your AC" book helped understand how the systems worked and often gave oil capacity specs and other useful stuff. Another thing that has been good for my shade tree conversions, is to put a can of hose/ seal/ Oring conditioner in to slow or stop minor rubber part leaks in old R12 systems.
One bad thing about not removing all the old mineral oil, is that the condenser and evaporator area occupied by that old oil, does not cool . On a system with plenty excess capacity that means little, as the system still has enough capacity. If the system is marginal, like on a Dodge caravan, then that less cooling might make or break the deal.
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