No, you can not see anything.

The valve always has power to it and is "on" when there is no ground on the other pin to close the circuit. When "on" water flows. When the ground side is engaged by normal control or by jumper there should be no wster flow.

The only easy way to tell if the valve works is to see what happens to the duct temperature. Squeeze off the flow with some vice grips to verify that it will cool down.

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