Excellent Thread on Alternative Refrigerants

[gmercoleza]

http://groups.google.com/group/rec.autos.misc/browse_thread/thread/58679a880c80a71f/8f706bf8554d444b?lnk=st&q=r22+alternative+miscible&rnum=1&hl=en#8f706bf8554d444b

The whole thing is very interesting, but in particular skip down towards the bottom and note this logic:

R-134a has a couple of problems, when used in a system designed for R-12.

Firstly, the boiling point of R-134a is about -15F compared to R-12 at -21.6F. (at one Atmosphere).. This causes 4 or 5 degree warmer duct temperatures unless the system is modified by setting low pressure cutout lower to compensate. Variable displacement compressors, such at the GM V5 are difficult or impossible to modify, and always set the suction pressure at 28 PSIG.

R-134a has a lower "critical" temperature (214F) vs 233F for R-12. The critical temperature of a gas is the the temperature at which as gas will no longer condense to a liquid, no matter how much pressure is placed upon it.

When under the hood/condenser temperatures approach the critical temperature of a refrigerant, head pressures soar, and cooling performance goes down the tubes. Under the hood temps of 220F are not uncommon.

Other manufacturers market blends comprised primarily of R-134a and are "cut" with either R-142b or R-124, both of which have higher (warmer) boiling points than R-134a.

R-12 boiling point -21.6
R-134a boiling pt -15
R-124 boiling pt +10
R-142b boiling pt +14

So, how is adding 20% - 40% of R-124 or R-142b going to make the refrigerant any colder than R-134a is already without having a "balancing" ingredient in the colder direction?

R-406A contains 55% R-22, and R-414A contains 51% R-22 to produce a correct temperature-pressure relationship which closely tracks R-12 and doesn't require changing the oil nor the pressure controls. R-22 boils at -44F.