Very useful info, thanks. Yes, the switch I ordered was a temprature switch that screws into the receiver-dryer and switches on the fan. One tech with whom I spoke advised wiring the fan directly into the compressor clutch circuit so it comes on when the a/c comes on. I have the switch jumpered so the fan runs all the time in summer.
He also advised that he simply bypasses the ecr unit on 123 cars to avoided the expense of replacing them. If the temperature gets too cold, I can switch off the a/c.
I have been poring over the schematics of the climate control system ( as opposed to pouring sweat while it was off) and have concluded that the engineer was exacting revenge for the Allied destruction of the M/B works in WWII.
When Dr. Porsche was captured by the French, he designed the Renault 4CV as a POW, which has been known ever since as “Porsche‘s Revenge.”
Thanks again for the info. Saved me much time and hair-tearing.

__________________
Stage Wizards Lighting and sound designer
1981 SD 328,000
1985 300TD, 266,000
1984 300 TD, 267,000