R421a Problems and Benefits
In the wide choice you have today's on R22 replacement, one product stands out from the crowd to be the only two components blend.
Less components mean less fragmentation at high temperatures and the patented lubricant additive guarantee oil return to the compressor without the use of any Hydrocarbons.
Refrigerant Guys labs tested R421a on mid temp systems and found no particular problems.
After the retrofit to R421a we monitor the system and we found no significant difference in pressure, compressor temperature and efficiency (air temp at the vent and Amps drained).
Remember this product as a lubricant which is compatible with basically any oil (Mineral, POE or AB) and the manufacturer claims no oil drain/change is required for any application for any application with less than 20 feet line or less than 20 feet drop in high between compressor and evaporator.
In case you have a system that exceed this requirements the manufacturer suggest to convert the oil to POE, however Refrigerant Guys suggest to stick with the old R22.
In the 2018 prices of R22 decreased significantly due the large overstock in the country and alternative Refrigerant became less attractive to customer, however you may want to consider retrofitting your system away from R22 not just for an environmental choice, but also to guarantee price stability for the years of the unit left in service.