Dave -

Interesting timing on your post. I just changed my 124 diesel wagon from R-134a to R-12 last night.

I went through about the same process as did you. Everything got replaced - evaporator, compressor, condenser - everything. I got lazy and used a stock condenser instead of fitting a parallel flow. Perhaps as significant as all the other repairs, I replaced all the vacuum actuators. The car no longer wastes any cold air out the defroster vents, and 100% reciculate mode is definately 100% recirculate mode. Stinky cars up ahead no longer fumigate the interior of this 124.

Like you, I used a universal synthetic refrigerant oil that operates with both R-12 and R-134a. I elected to initially charge with 134 because it was so much cheaper - better to lose a $10 charge if had a problem.

Surprisingly, the 134a worked pretty well in the 124. This is a combination everybody says doesn't work, but I found it OK. It worked great all spring and into the early summer. It was adequate even on our 100 degree days. If the car had been sitting in the sun, it took about 10 minutes of stop-and-go driving to become fully comfortable inside.

I used an a/c thermometer to measure the temperature of the air discharged by the system. On the highway after dark it would put out 39 degree air, after the blower had slowed . During the day, with the fan speed up reasonably high, it would deliver 50 degree air in stop and go driving. Sitting at long traffic lights in 100 degree ambient temperatures it would creep up to 60 degrees. Accelerating away from the light it would rapidly cool down.

Now that may not sound so great, but surprisingly it kept the car comfortable. I think a lot had to do with fixing the recirculate function. When the car is not drawing in hot, humid air, the system does a better job of dehumidifying the interior of the car. Removing moisture from the air is a big part of why air conditioning makes us more comfortable. I guess very dry 50 degree air will actually do the job on a hot day.

System pressures with the 134a were OK. I charged until the low side came up to ~25PSI with the engine at 2000RPM. High side settled in at ~325PSI under those conditions - a touch higher than I like. But that's in my garage without good airflow over the condenser.

I don't have any performance figures for the R-12 yet, but will follow up when I have some data.

How come you think your temperature numbers are fouled up?

- JimY, fellow a/c hacker