Various ways to test effect.

Actually, you do not need the temp wheel in any position for the A/C compressor to be on. All you need is to not be in the economy position.

The PBC will ground the signal from the Klima/MAS/BASE (depending on year/model) telling it to turn the compressor on in any PBC position except econ. The temp wheel does not decide whether to have the compressor on. That decision is totally based upon the PBCs evaluation of the evap temp sensor and possibly intervened with eng temp.

The temp wheel only is a variable sensor whose signal is compared to other sensor values in deciding how much to blend regulated heating and regulated refrigeration.

If you wish to see the regulation by temp switch, heating it would probably be easier to see as the control of the heater core temp is influenced by the temp setting on the wheel. If you look at the water control valve signal it should be 100% closed duty cycle at "Min", it should be 0% duty cycle at "Max", and the duty cycle should vary in between by the temp wheel setting and the temp of the day.

BTW, the easiest way to view the compressor on signal to the Klima/Mas/Base is at the low pressure switch on the drier. It passes through the normally closed pressure switch on the way to the compressor control section of the power relay Klima/Mas/Base.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician