Dave -

I think you've got a good plan. Feedback from those who have used a parallel condenser is that R-134 provides reasonable performance. Certainly R-12 is ultimately better, but it may not be truly necessary. At any rate, getting the 609 license is trivially easy - I've had mine since before the internet...

I think the limiting factor in around town performance is the compressor, rather than the refrigerant. At idle, the low side pressure rises to ~45PSI, which means evaporator temp is about 45 degrees. Typically discharge air is 10 degrees above evaporator temp, so think 55 degree air. This is about the upper limit before the air begins feeling clammy rather than cool. I don't know of any way to solve this problem, other than move to the sticks like Larry

One advantage of staying with R-12 is that you don't have to use PAG oil. PAG is nasty stuff - it's a skin and eye irritant, and of course it is very hygroscopic and will certainly introduce water into your system.

One suggestion. The 123 chassis was designed by MB to utilize 80% recirculated air/20% fresh air when in recirculate mode (basically all summer here in Texas). It can be modified to use 100% recirc. I did this back when I owned a 123. I found this mod reduced duct temperatures about 5 degrees on the hottest days. It's quite easy, and well worthwhile. I may have the instructions buried somewhere on my PC.

I've got a vacuum pump and guages, which you're welcome to borrow as well. I bet Larry's are better That said, our offices are across the street from one another (I'm looking at Larry's building as I type this), so it's not like you can save a bunch of driving.

Gotta run to a meeting.

- JimY