how to convert your car ac r12 system to r134a (4 steps)

a guide on how you can convert the ac system of your car from refrigerant type r12 to the more modern and environmentally friendly refrigerant type, r134a.

r12 to r134a conversion

if you drive a car that was manufactured before 1994, it’s possible that the air conditioning system is still using r12. this refrigerant was deemed to be dangerous to the environment and it must be replaced with r134a instead. however, you might not know how to convert your car’s ac r12 system to r134a. 

you must first discard the old r12 refrigerant properly and fit the air conditioning system with compatible ports and equipment. only then will you be able to pump up the system with the r134a refrigerant and ensure your system is compliant. 

in this guide, we evaluate how to figure out the appropriate amount of r134a to add. we also look at the steps to convert the system from r12 to r134a. 

how to calculate how much r134a is needed

r134a refrigerant is lighter than r12. to ensure the right charge, you must fill the new system with between 75 and 85% of the factory-set capacity for optimal cooling. 

to discover the capacity for refrigerant, you want to use the specs for the current system and multiply the r12 charge by 0.9 or 90%. subtract ¼ or 0.25 pounds from this number.

however, r134a isn’t going to cool the same as r12. even if you charge the system properly, you might notice it doesn’t get as cool. still, r134a is much more tolerant against under and overcharging. 

how to convert car ac r12 to r134a

the steps below are how you can easily convert your r12 to r134a in an older car. this is not the right way to convert your system, because you want to replace all o-rings, new accumulator, new filter and so on. but we’re talking about a cost over $ 2000, so it’s probably not worth doing all this if your car is old

for many car models, there are specific conversion kits that contain the necessary parts for the conversion. in some models you also need to replace the pressure switches.

but just replacing the fittings and filling in the right amount of r134a will work well on most car models, but is not a permanent result. we do not recommend that you do this and you do it on your own risk:

1. discard r12

before you do anything else, you need to pump out the r12 refrigerant that is currently in the system. this should always be done by a licensed professional because it must be disposed of properly. 

if you release r12 into the environment, you could get in trouble. not only is it bad for the environment, but it’s illegal. 

2. retrofit the system

you must add new fittings to both the low and high side service ports on the ac system. turn the low side fitting over the existing part. you will need a wrench to tighten it to factory torque specs.

put the high side fitting over the old connector. use a wrench to tighten this to the appropriate specs as well. you want to add the retrofit label on the connectors so other people who buy the car after you know to use r134a.

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3. hook up gauges

all of the valves on the manifold gauge should be closed. connect the low side port to the blue hose and put the red hose on the high side port. the yellow hose goes to a vacuum pump.

start running the pump and open both valves on the gauges. you want to vacuum down the system for at least an hour. once you are done, you close all of the valves and turn the pump off.

related: ac low side pressure too high – common causes & repair costs

4. pump in r134a refrigerant

use the yellow hose to connect to the r134a can. this refrigerant should already contain oil. otherwise, you will need to add that separately. 

turn the valve on the top of the can. start the car engine and turn your air conditioning on as high as you can. you can place a thermometer in the vent to measure the temperatures blowing out.

with the blue hose connected to the low side port, you want to open up the system so it can draw the refrigerant from the can. continue adding the r134a until you have reached the appropriate capacity, which is less than what was needed with r12.

when you are finished, close the valves on the gauges and disconnect them. put your gauges back into the carrying case, so they are protected from damage.

cost of converting an r12 to the r134a system

if you have a professional convert the r12 to r134a, you may spend about $250 for the entire service. however, this is much more cost-effective than replacing the entire air conditioning system. 

if you were thinking about getting an r134a system installed, your cost would be around $2,000 to $4,000. usually, it’s not worth going this route, especially when you can simply retrofit the existing equipment.