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How to convert from R12 to R134a

coldstar on Thu September 26, 2013 9:24 AM User is offlineView users profile

How to retrofit air conditioning systems

I always start with a good visual inspection of the entire automobile air-conditioning system. I look for any obvious problems like chafed lines or wet spots that may indicate a refrigerant leak.
Next I run a good performance test. I will record the temperature at of the ducts and also the pressure readings on the gauges. This is before I perform any repairs to the AC system.
Next I will remove all of the old R12 from the system with an approved recycling machine. In our shop, we have a special machine just for r12 systems.
This next step is necessary and a lot of people will skip it. Your A/C compressor will require an oil change. R12 and R134-A use different refrigerant oils. It is necessary to remove the air-conditioning compressor and drain out all the oil. I always measure the amount of refrigerant oil that comes out and install the same amount using approved r134a pag refrigerant oil.
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If the vehicle is equipped with an expansion valve I remove it and clean it. If the system has an orifice tube, I will usually replace it. This is because the orifice has a screen on it that can become partially clogged. Also, this part is usually only a few dollars.
Then you remove the receiver dryer or what is also called the accumulator. Again you drain the refrigerant oil out of this part and measure the amount that comes out. Next you will install that amount of 134a system oil in the new accumulator. Note that replacing the accumulator is highly recommended at this point. Especially if the system had no Freon in it before the conversion process.
The next step in retrofitting air-conditioning is to permanently install the components that you removed with new O-rings. A good tip is to coat the new O-rings with 134 a refrigerant oil you have been installing in the system. This will increase the lifespan of these O-rings and prevent any small leaks from appearing.

Now most of the work is behind you and the fun part begins. It is recommended that you permanently install the conversion fittings, using a thread locker such as Loctite. Note that these fittings are supplied in a conversion kit that can be had at any parts store. The kit comes with a conversion label you must apply to the vehicle.
Next you'll want to pull a vacuum on the system for at least 30 minutes. This will remove any moisture and impurities that entered the system while it was disassembled. This is also a step that is often skipped when people are in a hurry. Doing this truly adds longevity and reliability to the air-conditioning system.
This next step is important because it is time to recharge the system. The rule of thumb is that the replacement R134A Freon is about 80% of the R-12 charge. If you charge the same amount as originally installed the system will not function properly.
Next you'll want to run an AC performance test on your new retrofitted air conditioning system. The temperature may be a degree or two warmer than it was previously and this is a normal condition. Also note that your pressures may also be slightly higher on both the high and low sides. The target low side pressure is about 35 psi. But this will vary with the outside temperature.
Converting auto air conditioning

The above procedure is my opinion on the proper way for retrofitting air-conditioning systems. I have seen do it yourself car mechanics as well as professional ones skip several steps that are listed above.

The AC system might operate just fine when finished. The question is how long will it last before a problem develops. Performing all of the outlined steps above will often result in a more reliable automobile air conditioner system for years to come.

If your auto mechanic is performing these repairs, print out this page and ask him to follow all of the steps that are outlined. Or quiz him on the retrofitting air-conditioning procedure and ask for the old parts!conversion

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