System Differences

A system that is charged with one type of refrigerant can become contaminated when serviced with equipment that is used for other refrigerants. The system can be damaged by these contaminants; resulting in costly repairs; and when the contaminants get into the servicing equipment they can spread to other vehicles like a virus. To prevent this; industry standards have been developed so that an A/C system designed for one kind of refrigerant cannot accept equipment designed for another. Underhood labels on each vehicle clearly state the factory charge by type and amount of refrigerant. Fittings on R12 systems are not the same as those on R134a systems. Unlike R12 systems which typically use threaded service fittings for the high and low sides; R134a systems use quick coupler fittings without external threads. The high side has a 16 mm O.D. fitting while the low side has a 13 mm O.D. fitting. R12 system fittings are 7/16"-20; R134a fittings have 1/2"-16 Acme threads.

Since R134a is made up of smaller molecules than R12; R134a tends to leak through hoses easier than R12. For this reason, service hoses for the two refrigerants have different specifications. Service hoses for R12 are marked "SAE J2196". The low-side hose is solid blue or black with a blue stripe; the high-side hose is solid red; or black with a red stripe. The utility hose is either solid yellow or white; or black with yellow or white stripe. Service hoses for R134a are labeled "SAE J2196-R134a" and are color-coded as follows: solid blue with black stripe for the low-side hose, solid red with a black stripe for the high-side hose, and solid yellow with black stripe for the utility hose.