It is a well known fact that running the AC system can drastically reduce gas mileage, so I did what I could when I replaced my AC compressor last year to improve its efficiency, and therefore reducing the amount of power it wastes while also improving performance.
The first thing I did was I tuned up the system the best I could. I removed and flushed the evaporator as well as all of the AC lines, I replaced all of the seals as well as the TXV and the filter dryer, and I insulated the low pressure AC lines before I reinstalled them to reduce the amount of heat they absorb from the engine compartment. The less heat the refrigerant absorbs, the less pressure the compressor will build and the less power it will take to run.
Then I turned my attention to the condenser. Since it was from 2005 and the car had over 220K miles on it at the time, the fins were bent beyond repair by flying debris. Even though the condenser didn't leak refrigerant, I replaced it with a new Denso condenser, which cost around $60 with shipping. In my opinion, replacing the condenser while the system was open was well worth the money to improve efficiency and prevent leaks in the future.
So once I reassembled the system, I evacuated it overnight with a vacuum pump to remove any air or moisture and I refilled it with 4 ounces of double end capped PAG oil, which apparently has better lubricating properties and isn't hydroscopic. I then added 19 ounces of pure R134A refrigerant, which is within the factory spec of 17.6 to 19.4 ounces.
After all of that work, the AC worked pretty good, I would say at least as good as when the car was new, although this car's AC never worked great, especially at idle.
But about 1 month later, I decided to try Envirosafe Industrial R134A replacement. It is basically a 60/40 blend of propane and isobutane, so it's a flammable refrigerant and I wouldn't suggest trying it.
So I took the car to a shop to have the refrigerant recovered, then I took the car home, evacuated the system for over an hour to remove any remaining R134A refrigerant, and filled the system with about 7 ounces of Envirosafe Industrial R134A replacement, which they told me is approximately equal to 19 ounces of R134A.
I immediately noticed that the system cooled off quicker, and it got colder at idle. Also, this refrigerant runs at a lower head pressure than R134A, so the AC compressor doesn't draw as much power to compress it. Not only will that improve gas mileage, but it should extend the life of the system too.
But as soon as I drove it on the highway, I noticed that the compressor cycled on and off more. With R134A it pretty much ran constantly on a hot day, but with this refrigerant it cycles on and off instead of running constantly, which should save some gas.
I also "feel" like the AC doesn't create as much drag while it is running with this refrigerant due to the lower head pressure, but I can't prove that.
Anyways, let me know what you think about this
