1993 Mazda Miata

1990-1993 Mazda Miata Air Conditioning System Diagram​​​​​

The original Mazda Miata, 1990-1993, used a refrigerant gas called R-12. The gas works very well in A/C systems, but is quite hard on the atmosphere. With time, refrigeration systems moved on to a more environmentally friendly gas called R-134. The EPA has progressively passed regulations making R-12 gas expensive to work with, expensive to purchase, and difficult to find.
​While the reasons behind this are sound, it can make working on and maintaining an older A/C system a bit tricky. Often older cars, like this Miata, receive an "R-134 conversion" but this is typically a very basic conversion. It largely consists of simply draining an old R-12 system of the R-12 gas, replacing the system's filter (called the drier), and then refilling the system with R-134 gas.
This process can work, but it is a compromise. R-134 gas, while better for the environment, is not as efficient as R-12 at actually cooling. This means that a cooling system designed for R-134 has all the components in it's system designed specifically to use the less efficient gas.
​When you put R-134 gas into an R-12 system, the components aren't able to get the most out of the new gas because it doesn't cool as well.
​So a lot of the time you're left with a system that cools "okay", but not like it used to when it used R-12. Sadly, without a proper conversion, it is about as cool as the system can get.

While the process is much more time consuming, and expensive, the best way to convert an R-12 car to use R-134 is to use components made to get the most out of R-134 gas. For this example Miata, while the 1990-1993 model years use R-12, years 1994-1997 upgraded to R-134 gas. This means that since the overall designs of the cars are the same, a complete R-134 system can be installed into an older Miata allowing it to use a more modern A/C system with refrigerant that is cheaper to work with, easier to obtain, and cools very well when installed in the correct system. This superior conversion will replace every component shown in the above diagram except for the fan and it's fan shroud. First, the older system needs to be completely removed. Removal of the system means pulling out the radiator, some components of the dash, and a few items off the front of the motor.​ So, it's time to get to work. Click on the pictures to follow along.

After the removal of the old system, it's time to install all the R-134 system components with new seals and the proper oil.

After A/C work that involves opening the system up, it is necessary to apply a vacuum to the system to remove air and moisture. This also pressure tests the system to check for leaks. In the picture on the left the leftmost gauge shows negative 29-30 inHG, while the right gauge is bottomed out at zero. This is a good hard vacuum. If the system can hold this vacuum for an extended time, we know the system is sealed and ready for business.

Once it passes the vacuum test it's time to add the R-134 gas, test performance, and enjoy that cool breeze. After complete installation the car has a more modern, more environmentally friendly air conditioning system that looks factory and professional.

The photo is hard to make out, but the system stays between 42-48 degrees at the vents. Enough to keep you cool in the summer.

The system looks almost exactly like the original, but the devil is in the details. These R-134 specific parts will give much better cooling performance.