Do a test:
Move the antifreeze valve to one stop and then turn on the pump. If you have suction, the antifreeze valve is open.
Then turn the antifreeze valve to the other stop and test for suction with the pump on again.
If you have suction at both settings, the valve is broken and that is the cause of your problem.
If one of the settings shows no suction, that is the closed position. Leave the antifreeze valve in that position and make sure the other valve is in the opposite position.
The system will never operate with both valves in the same position. They must be opposite each other so that the pump draws from the water tank or an antifreeze bottle. Never both. Never none.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!