Originally Posted by jcyuhn

He has reasonable cooling at road speeds, it's the idle that's not so great. With a low side pressure of 55PSI there is no way to get good cooling at idle. Recall your middle school science class - the boiling point of a liquid varies with pressure. Lower pressure equates to lower boiling point. In the case of R12 the temperature at which it boils is approximately equal to the low side pressure (expressed in PSI) - one of the cool things about R12. Hence his evap is only at 55 degrees at idle, and the air coming off it is typically ~10 degrees warmer, depending of course on fan speed. Here's a link to R-12 & R-134 pressure/temp charts: http://www.ackits.com/aacf/ptchart.cfm

My 123 300D had the same OM617 & R-4 combo, and I had the same challenges. It was OK at speed - not great, but OK. At idle it really didn't cool well enough and the car really wasn't comfortable in the heat of a Dallas summer.

My solution involved selling the 123 and acquiring a 124.