There are 2 switches on the dryer on a 123.

The pressure switch is in the compressor circuit, it keeps you from frying the compressor if you have insufficient charge. The switch has large hex flats and does require evacuation to replace since it has to see the pressure of the refrigerant to work.

The temperature switch is threaded into the brass block on top of the dryer. This is the switch that triggers the fan. It has two quick disconnect terminals in line with the switch. A common DIY hack to have aux fan all the time is to unplug the switch and connect the two terminals together. This pulls in the fan relay anytime the key is on. The switch is simply threaded into a blind hole in the dryer (no connection to the refrigerant passages) since it only is sensing the temperature of the dryer body.

The temperature switch is cylindrical and if your dryer is stock the rear end of the switch is pointing straight at the radiator. It unscrews but as vstech and I found out it is easy to break. Phil has them.

Reminds me, I put mine back together with duct tape, and I need to replace mine. It works but I don't want to leave it like that.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech