When I do A/C work whether it be R12 or R134a I run a VOV [Variable Orifice Valve] regardless.

All of this discussion of refrigerant replacements is all well and good but here is the catch, most of us are doing work on our own cars or people's cars where the envrionment is tightly controlled. I don't think any insurance company in NC is going to write me business insurance that will cover me putting propane into someone's car. So what are my choices?

R12 - Dichlorodifluoromethane: The original refrigerant gas of choice and mainstay of most cars until the 1994 model year. Now running $40-50 per pound. New virgin production ceased on Jan. 1, 1996 though a few bootleg countries are making it. However as the number of R12 vehicles on the road needing R12 recharges dwindles supplies & costs should stabilize for the near long term.

Advantages: Cools really good; most all cars from when a/c first was available until 1994 had R12 systems so a/c equipment was designed to run efficiently on it.
Disadvantages: Supply and Cost while still available recharges are downright expensive.

R134a - Tetrafluoroethane
OEM replacement, all cars (I believe so) from the 1994 model year on carry R134a. Smaller molecules than R12, smaller cooling capacity than R12 runs at higher temp & pressures than R12 especially in converted systems. Preferred convertible refrigerant due to availability, industry and liability acceptance. Recommended use of VOV for performance. $6 per can.

Advantages: OEM acceptance; industry acceptance; relatively cheap (compared to R12; adequate supply and distribution for home or professional.
Disadvantages: Poorer performance especially in converted systems; may leak out of older conversions; performance can be mitigated by use of VOV.

R22 - Chlorodifuoromethane
Mainly used for industrial and home appliance applications. I have seen this used in automotive applications but its closely linked to R12 and thus going out of favor. Costs and supplies are sometimes problematic like R12 but not as bad. Still in production but being phased out. $76 per 30lb.

Advantages: Kissing cousin to R12 and thus wide acceptance in non-automotive applications.
Disadvantages: Same as R12 though supply and costs are not at R12 levels yet. Industrial use so industry acceptance and liability in automobiles is minimal.

R408a - Similar to R502 blend of R22, R125, R143a used in industrial applications for heavy duty cooling. Production slated to cease in 2020. Advantages are that it is in use and cools really good disadvantages confined mainly to industrial applications.

R409a - Blend of R22, R124, R142a closely resembles R12. Production slated to cease in 2020. Preferred industrial conversion refrigerant. Advantages like R134a for cars industrial acceptance, OEM acceptance, cost and availability. Disadvantages acceptance in auto a/c systems not widespread.

R404a - Blend of R125, R143a, R134a. Closely resembles R502 and the long term replacement for R408a. Slightly less efficient than R502 and R408a. Industrial and OEM acceptance. New industrial and commerical equipment slated to have OEM R404a 2006. Advantages same as R408a, disadvantages it hasn't reached acceptance in automotive industry yet. $275 25lb cylinder.

R406a - (dead site) http://www.autofrost.com 'AUTOFROST' EPA certified for automotive use; miscable with mineral oil. Performance comparable to R12 in converted vehicles. It returns oil to the compressor. Runs about $20 per pound.

CoolTop - (dead site) http://www.cooltop.net is a Drop in replacement for R134a. System can be topped with CoolTop without removing R134a. Manufacturer claims will lower temps 10 degrees. I wonder what CoolTop and a VOV will perform. Has a patented chemical that isolates moisture. Cans are $18.

FRIC-12 - (dead site) http://www.refimax.com/products/fr12_faq.htm>

FREEZE 12 - (dead site) http://www.technicalchemical.com/products-11a.htm

Johnsen's biggest claim is they make a lot of a/c handling equipment.

FREEZONE - (dead site) http://www.freezonerb276.com/freezone.html

NU22 - (dead site) http://www.icorinternational.com/

The things that drive what I put in people's cars is:

1) Cost
2) Availability
3) Material Handling
4) Future Serviceability

The biggest problems I have outside of R12 & R134a is that if I put something like FREEZE 12 in a customer's car they drive off and good luck finding someone who uses the alternative. I *know* of only 3 shops in Charlotte that have the necessary equipment to regularly and legally service anything besides R12 & R134a. Then try and explain what 408a is to a customer who cannot fill their own tires... I would be curious to see what alternatives work with VIR & STV & hot gas bypass systems.