The valve is held closed with battery voltage. It does this for sure only in the "Min" position of temp control. In this case if one put a volt meter across the two terminals, while in one's hand (not connected to nothing), one would get battery voltage (or close).
In any position but min the ground is applied in a pulsed fashion! Off..on..off..on..etc. depending on the temp decision. Using a graphing multimeter (GMM) it looks like a square wave of varying duty cycle and frequency.
Grab the hose either side in a convenient spot. Take a section of old hose and cut it such that it can be placed under the vicegrips so the visegrips don't hurt the installed hose. Don't squeeze at bends, squeeze in the middle of the most convenient long straight section.
Bosch Master, ASE Master, L1
33 years MB technician