One Shop's Experience Retrofitting Motor Vehicle Air Conditioners to HFC-134a

Many technicians are looking for the proper procedures to retrofit vehicles to R-134a. Although EPA does not have the technical expertise to recommend procedures for each vehicle that may require retrofitting, here are some recommendations from one service facility and parts wholesaler, Arctic Auto Air in Fort Lauderdale, Florida, that has been recognized as a pioneer in retrofitting.

This information is being provided solely as a service to automotive technicians, who should rely on their experience and judgment to determine the most appropriate steps in retrofitting each vehicle that comes into a shop, whether the new refrigerant is HFC-134a or another substitute. Neither EPA nor Arctic Auto Air warrants or guarantees any of this information. EPA has not tested any of these procedures and does not endorse them. Technicians may discover that this information contradicts other information provided to them by automakers or by suppliers. Nevertheless, EPA believes technicians may find it valuable to see the recommendations of one shop that has completed over 1,000 retrofits.

Arctic Auto Air's Retrofit Procedures

Recover the R-12 according to SAE J1989 standards.
If the system is contaminated, perform closed-loop flushing.
After any necessary parts replacement, add a PAG or ester oil to whatever exact specs the automaker recommends for mineral oil. Too much oil will affect the performance of the system.
If you have not already done so as part of the repair, replace the accumulator or drier -- make sure that you use an R-134a-compatible desiccant such as XH-7.
Install the R-134a service ports. Remember that depending on the design of the ports, you may have to remove or replace the schraeder valve cores. The service ports for R-12 are the opposite for R-134a: the large port is on the discharge side and the small port is on the suction or low side.
Evacuate the system for 45 minutes after it reaches 29.5 inches of vacuum. A retrofit requires longer evacuation time to ensure removal of the residual R-12.
Charge the system with R-134a using a calibrated charging cylinder or weighing scale.
The retrofit will generally require an R-134a charge that is equal in weight (# of ounces) to between 75 and 90% of the original R-12 charge. Start with an R-134a charge that is equivalent to 75% of the recommended R-12 charge. If there is excessive clutch cycling, add up to 5% increments of R-134a. Do not exceed 90%.
Leak check vehicle.
Fill out and apply retrofit label over original R-12 label.
Test drive vehicle.
Do a performance check. High-side pressures should be within 10-15% of established R-12 pressures.

Tips from Arctic

On most vehicles, the duct temperatures of R-134a versus R-12 are generally the same. On some vehicles, the duct temperature is colder by a few degrees and in some instances on rear wheel drive domestic vehicles, the duct temperature may be 2-4 degrees warmer at idle.

The high-side pressures at idle generally remain the same on front wheel drive vehicles with dual electric fans. High-side pressures at an idle are sometimes higher in rear wheel drive vehicles by approximately 10-15%. However, this increase in pressure should not affect the performance or durability of the system.

General Motors

On clutch cycling orifice tube systems, adjust the cycling switch counter clockwise to 21 psi cycle off.
On full size front wheel drive vehicles with a single engine cooling fan, an auxiliary electric cooling fan may be needed.
On smaller front wheel drive vehicles, the single engine cooling fan is adequate.
On 1988 to 1992 Cadillacs, replace the low temperature evaporator sensor. This will alleviate a false reading of codes 46-47, which means low inlet evaporator temperature, rapid cycling or plugged orifice tube.
On rear wheel drive vehicles, as long as the fan clutch and cooling system are operating well, only adjustment of the cycle switch is required.
Chevy Suburbans with single air may need an auxiliary electric cooling fan. On full size vans and Suburbans with dual air, add an electric auxiliary cooling fan.

Ford

On vehicles with clutch cycling orifice tube systems, adjust the cycling switch counter clockwise to 21 psi cycle off. Full size Broncos and vans may need an electric auxiliary cooling fan.
On pickups without heavy duty cooling packages, an electric auxiliary cooling fan may be needed.
On rear wheel drive vehicles, as long as the fan clutch and cooling system are in good operational condition, only the adjustment of the cycle switch is required.
On Aerostars, when a leaking condenser replacement is necessary, replace with a new motorcraft YJ351 multiflow condenser.

Chrysler

On rear wheel drive vehicles with a thermostatic switch, no adjustments or modifications are needed.
On Caravans and Voyagers with single air and without pressure cycling switches, no adjustments or modifications are necessary.
On vehicles equipped with variable displacement compressors, no adjustments or modifications are necessary.
On front wheel drive vehicles with thermostatic switches and a two blade engine cooling fan, an auxiliary electric cooling fan will be needed.
On vehicles with pressure cycling switches, rapid cycling occurs due to the lower evaporator pressure. These switches are not adjustable. However, they can be replaced with an adjustable thermostatic switch which is secured at the outlet of the evaporator. Install a low pressure protection switch into the expansion valve and wire these two switches in series.
On Caravans and Voyagers with dual air, due to the lack of condenser cooling capacity, stay with R-12.

Imports

On early model Toyotas and Nissans with POA valve systems, the evaporator pressure is lower with R-134a. Adjustment of the POA valve is required. Turn the pressure regulator adjustment screw approximately one quarter turn counter-clockwise.

On Mercedes that do not have auxiliary condenser fan switches that close at approximately 225 psi, replace the switch with a switch that does close at that psi. All other vehicles require no adjustment or modification.

Top of page