Working on my ac. So far...

Verivied 12v getting to klima
Verified that pushbutton unit sending signal to klima
Verified slight resistance at pin 7 to check clutch coil resistance
New blower motor.

I want to do another test and check clutch coil resistance at connector on the compressor. It has wires going into it - Yellow White White. I checked for resistance on the pin on the compressor where the yellow wire fits and got slight resistance. Nothing registered on my multimeter on either of the two pins where the white wires fit.

I reconnected Yellow White White wires to compressor then jumped 5 and 7 in the klima socket and started it up. Ac clutch still did not engage.

I suspect the coil, but I would like to verify it. Is there a simple way to check for voltage with a test light or multimeter?

I listed Duovalve in the title because all of a sudden, the coolant expansion tank is well above the normal level. Does anyone know of a connection between a failing duvolve and the ac system? The duovalve in my car is the second one. I replaced the original back in 2008 (when I didn't need two sets of eyeglasses to work on my cars)

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900