The 120 psig both sides w/ AC off on a 70 F day sounds high to me. In my two 300Ds' (one w/ R4 compressor, other w/ Sanden), I usually measure 70-90 psig and is usually hotter here. 25 psig low side running is not abnormally low on a 70 F day. I usually measure 15 - 45 psig, depending on ambient temperature. I am currently using Duracool, which is similar temps to R-12, and recall similar pressures w/ R-12.

I second that the aux fan not running makes a big difference. We were stuck in a 2 hr traffic jam on I-5 in my 1984 300D on a 115 F day and the AC wasn't blowing very cool, so had to open the windows. Once we started moving, the AC was cold. I later found that the fan temp switch was bad/erratic. I tested 3 temp switches on the stove and found all go close at 86 F => "all summer" here. I don't know if other sensors or actuators get to vote on turning on the rad fan, perhaps the AC clutch also has to be engaged.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans