I have a 1982 300 TDT. The AC on it went out about 5 years ago. The compressor went bad and I had it replaced.
The owner of the specialty AC shop I use in Las Vegas, Auto Air and More, will not use rebuilt compressors. He says that he has had too many reliability problems with them over the years, and so he only installs new compressors. The price difference is not much. You also have to install a new cleaner/dryer when you replace the compressor.
I don't know if it was because I changed the compressor and the system began to operate with greater pressure or if it was just the age of the car, but after I replaced the compressor the evaporator and condenser and 4 of the hoses began to develop slow leaks, so I had to replace those too eventually. I have spent about $2000 on my AC in the last couple of years.
At the time, the shop recommended using Freeze-12, which is a refrigerant that is environmentally better than R-12, but is compatible with the type of oil, mineral oil, that is used with R-12. Freeze-12 is a more efficient refrigerant than R-134a, but is still not quite as good as the old R-12. R-12 works well enough to keep cool in Death Valley on a hot day. I am not confident that my system would work that well with R-134a.
I live near Death Valley where we see temperatures in the 120 F range nearly every day from mid June until early September, so AC is necessary here.
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At the web site above you can purchase Freeze-12 in kits that allow you to recharge the system yourself. EPA regulations allow anyone to work with Freeze-12. You have to have a license to work with R-12, so Freeze-12 also has the advantage of being able to do it yourself.
If you do change over to R-134a you have to make sure that you purge the system of the oil that was used with R-12, because R-134a is not compatible with mineral oil, and it supposedly turns into a gel in your system if they combine. I have not tried it myself, but a local mechanic here told me he put 134a in one of his cars without purging the system and it worked fine. But I would recommend Freeze-12 anyway, and so does he. Like I said, with our weather here AC is a vital necessity. You can buy the cans of Freeze-12 at any NAPA shop around here.
Here is a routine for filling the system. It sounds mysterious at first, but read it a few times if necessary, and it will start to make sense.
You only need about 95% as much Freeze-12 as R-12 because the molecules are different in size.
Jon E from Prescott, Arizona (337 days 23 hours ago.) Once your system is leak tight, contains the proper oil to match the refrigerant to be used, has been evacutated to remove any air and moisture contained therein, and has a metering device designed for the refrigerant to be used, then one may charge the system thusly:
- Attach the refrigerant container to the low pressure (suction) side of the system.
- Open the refrigerant container, thereby breaking the vacuum, and allow as much refrigerant to enter the system as will go into the static system. Then, shut off the valve to isolate the refrigerant container.
- Place a floor fan in front of the car so that air is directed against the condenser (located in front of or is part of the radiator) to simulate ram air (the air flow generated by a car's movement).
- Start the car and adjust engine speed (weight on foot feed?) to approximate approximately 40 mph.
- Place an accurate AC type thermometer in an air discharge duct which has the best air flow.
- Turn on the AC.
- Open all the car windows. (Note that the car needs to be in a warm environment of around 90 degrees f for charging to work best and most accurately.) This keeps the heat load on the evaporator (cold coil in the car).
- Check the thermometer continuously.
- As refrigerant is added, the temperature will come down for so long as the evaporator is not completely full of refrigerant.
- Go easy, adding a little bit of refrigerant and waiting upon the system to equillibrate.
- If the temperature drops, add a little more refrigerant and wait and watch for drop or not.
- As soon as you notice that the addition of refrigerant has not caused any temperature drop, you have the system charged to the point where the evaporator is maximally used. STOP adding refrigerant at this time.
- Dismantle your setup and you are ready to drive a car with a properly charged system.
This works with any refrigerant.
Note that R-12 could be charged as either vapor or liquid, with the caveat of not slugging the compressor valves with liquid. R-134a and other azeotropic refrigerants separate in the gaseous state and must be charged as liquid. Their cans are designed with dip tubes so that liquid comes out when the can is upright, just opposite of R-12 cans. Again, don't slug the compressor. That requires metering the liquid through a small oriface, which are available as individual divices, or by cracking the container or gauge-set valve and thereby causing the liquid to flash into vapor before entering the system.
I am not an auto mechanic, but an old retired HVAC tech who understands the physics and has charged all my autos thusly and those of my friends. Prior to this method, I tried all the other methods, such as, sight glass, pressures, and weighing it in. No method worked better or as well as this method.
As for converting a system, I beleive (as best as I can remember) that the oil and the meteing device should be changed when going from 12 to
134a. All systems should be vacuumed, although smaller systems used to be "blown out" with the refrigerant by many techs. All other considerations aside, that practice absolutely is illegal today.
If a system is empty when you start working on it, it needn't be recovered, but if any refrigerant is in it it must by law be recovered and properly disposed of, as must the old oil. Also, for residential and commercial systems, you by law must hold an EPA certification to open a system. I believe there is an automotive certification, but I am not certain if it must be held to work on automotive systems.