I noticed today the AC compressor on my W116 was not cycling. I taped an electronic temperature sensor to the suction line fitting at the compressor and saw it stabilize around 30*. The ETR switch in my car is set for 37* I believe. Is my switch bad or am I misunderstanding AC theory and the fitting is going to be way colder than the evaporator?

Is it staying off or on?
I'd want to put a set of gauges on it to see what the pressure readings were doing before I started nosing around the temperature switch.

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Jim

The compressor stays on full time.

I'm really looking to understand if the fitting at the compressor is 30 degrees, does that mean the evap is the same temperature?

As requested:

Ambient air 70*
Engine @ 1500 rpm
Low side: 20
High side: 150
Aux fan ON and additional fan in front of condenser.

Temp probe @ suction fitting 33*
Temp probe in evap: 57*
EDIT - I moved it to the coil loop at the end and was able to get 50*. I think my finger was skewing the results high though.
Thermometer in center vent: 48*

Obviously my temp probe in the evap is not making contact with the fins very well.

Any other thoughts?

Looks like you are running r134 refrigerant?

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Jim

No sir, R-12 with a parallel flow condenser, Sanden compressor, and new expansion valve.