This guide will go over what it takes to convert the older R12 Air conditioning system to newer R134A. The impetus for switching refrigerants is mainly for serviceability. R12 is an ozone depleting CFC refrigerant, and is no longer used or produced. This means that it is expensive to get and AC shops and mechanics will not service these systems anymore. R134A is a newer refrigerant that is not ozone depleting and is the current refrigerant in automobiles.
R12 and R134A share the same operating pressures. This allows you to retain your original compressor and hardware. The main difference is that R12 uses mineral oil to lubricate the compressor, where R134A needs a PAG oil, so this needs to be addressed.
R12 and R134A service ports are different and a conversion kit is required for the ports.
An R12 system converted to R134A is generally around 10% less efficient, but most of our old systems are low as is, so you will likely see an improvement, even with the lower cooling efficiency in a converted system. I have also cross checked the part numbers of the L300 AC compressor in both R12 and R134A models, and they use the same compressor. So Mitsubishi did not even change hardware for the newer 134A refrigerant.
R12A (another substitute) is also compatible with R12 systems. Unfortunately there does not seem to be much information about this refrigerant and it seems to be only made by one company, Red TEK. It is a blend of Propane and Butane with some other additives. It seems like R12A can be used to top off low systems, but should not be used for a full system charge, Again there is little information out there.
1. Generally Vans made before 1994 were all R12. Vans made 1994 and after are usually already R134A. It is best practice to replace the filter/drier during the conversion. This is especially true if your system has been empty for a while allowing moisture to get in. The desiccant in the drier can become saturated and useless. The drier is located next to the tandem condenser, behind the bumper, under the protective metal plate. The bumper does not need to be removed to access the drier, only the protective metal plate.
I have cross checked the PNs of R12 and R134A vans and the receiver is the same. This means the OE receiver is compatible with both R12 and R134A. *There are some desiccants that are not compatible with both*
OEM receivers are discontinued, both here and in Japan. Thankfully the 90s Supra used the same part. I was able to get an after market one at O’Reilly Auto parts for $30, one third of the OE list price.
PN: MRY 80-7987.
I tried a few before finding the right one. I ordered one that was listed as compatible from Rock Auto, but it was significantly smaller.
See below:
2. Next the service port will need to be converted to the push-to-connect style used in 134A systems. These conversion fittings are cheap and readily available. They just screw on to the existing R12 ports.
The service ports are located on and near the compressor. Blue is the low (suction) side- on compressor, red is the high (discharge) side- on discharge line.
3. Finally the R12 mineral oil will have to be flushed out and replaced with PAG oil. Thankfully these vans have a low mount compressor, which means most, if not all of the oil should be in the compressor (as it should be). Have a shop flush the AC system, add the oil, vacuum and recharge with 134A. If you still have R12 in your system, make sure the shop is willing to recover the old refrigerant. The new receiver should be installed at this time.
The amount of oil needed will depend on the size of your AC system. Below is a schematic of the large system with Dual AC and Cool Box. It is important to note that a controller is present and only allows one evaporator to run at any given time to balance the load. So the controller cycles between evaporators using in-line solenoid valves.
Below are the service manual charge tables for bot R12 and R134A systems:
It can be seen that the large size R12 system took 150cc of oil and the 134A system took 180cc. For the R134A system the Denso type 8 (ND 8) oil is equivalent to PAG oil of 46 VG viscosity (PAG 46).
So 180cc (180 ml) of PAG 46 should be added to the compressor. Then a charge of 42-44 oz of R134A can be added.