R12 to R134A Conversion

wptski on Sat June 08, 2013 9:08 AM

Year: 1990
Make: Buick
Model: Century
Engine Size: 3.3L
Refrigerant Type: R12

The AC is dead and probably very low if not empty.

Been reading lots about converting to R134A and watching some Youtube videos. The confusing part is the mineral oil that's still in the system. PAG oil is normally used with a R134A system but mineral oil doesn't mixed with R134A well. This brings up the use of POE or just called ester oil. I read some really detailed instructions on a conversion which stated that their are additives that allow R134A to mix with mineral oil then under the list of parts, it give a kit from AZ which is a pressurized can of ester oil.

If the system is evacuated or empty due to a slow leak most all the mineral oil with still be there. I've read that ester oil will absorb the mineral oil. The EPA site states that there should only be 2% or less mineral oil in the system with a conversion to R134A.

I read another rather lengthy paper on a conversion by somebody calling themselves the "GM Tech" in which they said that the mineral oil just sits there in system and doesn't harm anything.

So what's the truth about a conversion in general and using ester oil?

94RX-7 on Sat June 08, 2013 10:35 AM

Here's my understanding, and I'm breaking this down into two sections....chemical compatibility and lubrication ability. Chemical compatibility being the two chemicals can exist in the system together. Lubrication ability being the ability of the refrigerant to carry the oil around the system.

Chemical Compatibility:
Mineral Oil doesn't react adversely with R-12 or R-134a. Residual mineral oil in the system is OK when converting.
POE doesn't react adversely with R-12 or R-134a.
PAG doesn't react adversely with R-134a.
PAG DOES react adversely with R-12, although I've read that certain Double End Capped PAG oils don't react with R-12.
PAG doesn't react adversely with R-134a.

Lubrication Ability:
Mineral Oil is supposed to be excellent with R-12. Doesn't lubricate with R-134a because it doesn't carry the oil around the system.
POE seems to be regarded as a mediocre but acceptable lubricant with both R-12 and R-134a.
PAG works fine in an R-134a system.

wptski on Sat June 08, 2013 11:27 AM

By "Residual mineral oil in the system is OK when converting", do you mean after evacuation which could be a lot?

mk378 on Sat June 08, 2013 1:34 PM

Leaving a lot of mineral oil behind will reduce performance. It just gets in the way of refrigerant flow and heat transfer. Actually any kind of oil gets in the way of refrigerant flow and heat transfer, but that is a necessary compromise because has to be some oil in the system to lubricate the compressor.

During a conversion therefore you want to remove as much of the mineral oil as possible. This means taking the system apart to flush out the parts. Oil is not removed when the refrigerant is evacuated, or in most cases of a leak.

The Interdynamics claim about their magic oil being "miscible" are bunk. That kit will ruin your system. Do not use it.

Of course the most logical thing to do with a leaky R-12 car is to find and fix all the leaks and charge it with R-12. Nothing cools old R-12 cars like R-12 does.

94RX-7 on Sat June 08, 2013 3:07 PM

Quote
Originally posted by: wptski
By "Residual mineral oil in the system is OK when converting", do you mean after evacuation which could be a lot?

From a chemical compatibility standpoint, it doesn't really matter if there's a lot or a little.

As stated above, an excess of oil can impede heat transfer, and for that reason it is best to get as much as you can out.

wptski on Sat June 08, 2013 5:32 PM