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How exactly should R134a retrofit be done?

Leggie on Tue May 15, 2012 5:24 PM User is offline

Wal-Mart has a kit with fittings and three 12oz cans of R134a/oil blend.
I read the manual and its rather sparse. It just says that R12 needs to be removed properly before retrofit.

It doesn't say anything about draining existing oil.

How do I know the correct oil amount and type depending on retrofit situation? (i.e, lost R12, change o-rings and retrofit, vs replace compressor and retrofit)

mk378 on Tue May 15, 2012 6:56 PM User is offline

Do not use that kit. It does not work well and usually causes severe damage, thus the nickname "death kit"

In the "Procedures" section is a full procedure.

Major objectives for a succesful conversion include:
Consider not converting. If your system still has most of the R-12 in it, top up, diagnose and repair as needed. Nothing cools old R-12 cars better than R-12.

Replace as much oil as possible. This involves, at the least, taking the compressor off of the car to drain it. Remaining mineral oil in an R-134a system is worse than useless, as it just gets in the way and impairs heat transfer. Ester 100 oil is almost always used for conversions. It has the advantage of being compatible with R-12 if you ever want to revert.
Identify and repair leaks. Leaking R-134a is just as annoying and almost as expensive as leaking R-12 is. Never ever use a "stop leak" product, again they almost always don't work and almost always cause severe damage.
Use new o-rings on any connection you take apart, and on the line from the compressor to the condenser (those run hot, and thus harden with age and are very likely to leak) It's not strictly necessary to replace them all.
Always replace the drier. Make sure new drier is compatible with R-134a, any recently manufactured one will be, don't use NOS driers anyway.
Charge with plan R-134a, avoid any magic in a can. UV dye should be added to help locate future leaks. Try to use 100% of the specified weight for R-12 in R-134a. If you can't get to 80% without seeing excessive high side pressure, consider condenser issues.
Pull a good vacuum, using an electric pump (not air powered venturi type), before recharging. Air in the system seriously impairs performance and you will have to properly dispose of the air-contaminated refrigerant and start over.

Edited: Tue May 15, 2012 at 7:06 PM by mk378

Leggie on Wed May 16, 2012 3:54 AM User is offline

Something is seriously wrong. It needs a new compressor and/or TXV...
If I get a new-to-me compressor, I'm not sure which oil will be in it.

mk378 on Wed May 16, 2012 10:19 AM User is offline

It doesn't matter, even with a new factory compressor you should remove and replace any oil that comes in it. (Pre-filling compressors is an attempt to reduce warranty problems with those mechanics who just slap them on, but the oils used with R-134a absorb moisture from the air and thus can become "stale").

When rebuilding a factory system put in the car manufacturer's specified amount of new oil. Use oil that is sold separately as oil, not that which is combined with refrigerant under pressure.

Edited: Wed May 16, 2012 at 10:25 AM by mk378

Cussboy on Wed May 16, 2012 12:32 PM User is offline

Agree with what mk378 says. And consider staying with R-12.

Leggie on Thu May 17, 2012 11:28 PM User is offline

With a stock pile of 75 lbs of CFC-12, I should be good for a while.. if I can figure this out that is...

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