You have water flow if you have heat. The water valve (monovalve)is what controls the water. The valve is controled by the pushbutton control unit in order to achieve the asked for temperature.
The valve has three stages of control. it has power to it all the time and the PBC (pushbutton controller)grounds it to shut the valve. The three stages are: Min = the ground is always engaged the valve is always closed. Max = the valve is not grounded and the valve is always open. The third stage is everywhere else. In this position the valve is pulsed in increasing duty cycle as the called for temp is asked for. The controller compares the temp sensors and the asked for setting and pulses the water control to mix with A/C to get the appropriate temp. The farther the existing conditions are from the asked for state the longer the off or on cycle.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 03-30-2000).]