In this article we use the term '`retrofit" to describe the special procedures necessary to convert an R-12 A/C system to operate on R-134a refrigerant.
While some vehicle manufacturers have developed retrofit kits, we believe that for most cars there are less expensive ways to go. For example, retrofitting a Ford Bronco using a Ford kit can cost in excess of $600. Also depending on operating conditions, retrofitting procedures might vary on the same vehicle. Retrofitting a vehicle in Phoenix, AZ. would be different than in NYC
In this article we will look for the lowest cost retrofit procedure available and still maintain cooling performance comparable to R-12 systems or with cooling performance that although slightly reduced, would be sufficient to satisfy the customer. While the least costly retrofit procedure might not work on all cars it should work on the majority.
When retrofitting an A/C system, the first and most important step is to determine the condition of the existing R-12 system. Retrofitting a marginal system will not work. Since R-134a is less efficient than R-12, a system that is not cooling properly will only be worse after a retrofit. Also remember that R-134a runs at higher pressures than R-12. A system that is not tight or a system that has a slight leakage will most certainly leak after a conversion. We must also consider temperature in the conversion process. Temperature of the engine as well as ambient air temperature When engine temperature is too hot we cannot dissipate the heat at the condenser as well as a cool engine, and since higher pressure (R-134a) means higher temperature a cool running engine is essentia1 to a successful retrofit. This might mean the installation of an additional fan.
The first step, therefore, is a careful inspection of the existing R-12 system. Any worn components will have to be replaced, any hoses or O-rings that show signs of leakage will have to be replaced. The condenser surface will have to be clean without too many bent fins.
Once the existing R-12 system is determined to be good, we can begin the retrofit procedure. There is no such thing as a universal retrofit procedure, or a simple kit a technician can purchase that will provide all the necessary parts to guarantee a successful retrofit for every make and model. If we follow a few basic guidelines we can assure a successful retrofit for most.
When R134a was first introduced, it was thought that all non-barrier/ nitril hoses would have to be replaced during a retrofit, but later testing has shown that the mineral oil used in an R-12 system forms a natural seal. In most cases, the R-12 hoses will perform well, provided they are in good condition. This is also true for O-rings, unless the fittings have been disturbed during the repair or retrofit, replacing O-rings should not be necessary.
The mineral oil used with R-12 will not work with R-134a. Almost all new car manufacturers are using PAG oil in new cars with R134a. They are also recommending PAG oil on retrofits.. PAG oils have to be handled very carefully because they are hydroscopic ( they absorb moisture from the atmosphere), this oil muse be capped tightly when not in use The amount of mineral oil that can safely be left in the system after retrofitting, is still being debated. It was originally thought that any mineral oil left in the system would cause system failure. Many after market A/C specialists are choosing to use ester oils. Esters mix well with R134a and mineral oil at all temperatures, and any residual R-12 mineral oil left in the system will not have a significant effect.
Industry experts once thought that a retrofit would require replacement of the compressor. It has since been routinely accepted that most compressors that are functioning well with R-12 will continue to function well after retrofit. A few older compressors might have to be replaced.
Desiccants used with R-12 are not the same as desiccants used with R134a. Some experts recommend that the drier be changed on a retrofit, while others maintain that that is not necessary. All agree that if a system is opened for my length of time, the drier should be replaced anyway, so the installation of a R134a drier be done with the retrofit..
When retrofitting an R-12 system, certain legal requirements must be met, such as the installation of new fittings that will be unique to the refrigerant being used. The new refrigerant must be identified by a uniquely colored label, in order to identify the refrigerant in the system. All the R-12 must be removed before filling the system with an alternative and that EPA approved equipment must be used in order to recover the R-12 from the system
Keep in mind that although EPA has approved refrigerants other than R134a as alternatives, there is no such thing as a "drop-in" refrigerant, because the use of any alternative refrigerant must meet the requirements mentioned above.
To sum up, after the R-12 system has been carefully inspected and the remaining R-12 is completely removed, the system should be evacuated for at least one hour. When adding R-134a only fill to 85% of the R-12 capacity, watching the high side pressure carefully. It Is also recommended to change the high pressure cutoff switch to a R134a switch (one rated at 400#).