OK, first view of the R-12 performance in my 124. I've only driven it one day, so this isn't based on a lot of data. Thursday was a sunny and modestly warm day by Dallas standards, with a high temperature of 95 degrees.

The R-12 performed better during the morning commute, generating vent temperatures in the low 40s during my suburban stop-and-go commute. In comparison, R-134 would only drop to the upper 40s under the same conditions.

I ran some errands at lunch, when the temp was well into the 90s. Vent temperatures were perhaps 2-3 degrees lower than R-134 under the same conditions. I saw about 47 degrees with the blower running at a medium-high speed.

Heading home after work in mostly stopped traffic the vent temps were in the low-mid 50s - again, perhaps 2-3 degrees better than R-134.

When charging, the high side pressure was about 50PSI lower than R-134 under similar conditions.

Subjectively, the R-12 seems to cool down faster than the R-134. The air gets cold in less time. Though it does get a bit cooler, the difference isn't significant enough to notice without measurements. In both cases the car was comfortable at all times.

I don't think hard wiring the condenser fan will make any real difference. I have the newer red switch in place. The fan always comes on within a few seconds of bringing the car to a stop. It's pretty much running all the time that it will be useful.

I expect a parallel flow condenser would improve the performance of both R-12 and R-134 on the 124 chassis. However, another limiting factor is the compressor. The early 124 cars used a Nippondenso 10p15c compressor. Now, this is a nice little compressor, but the accent is on little. It has a displacement of 145cc. In contrast, the R-4 commonly used on the 123 diesels has a displacement of 176cc. In my opinion this makes a 123 a better candidate for conversion than an early 124. There's a reason Benz later switched to the larger 10P17c compressor.

OK, 'nuff rambling for today,

- JimY