I’ve a VMB4RY (build 1217) and a VMBLCDWB (build 1307)
My heating pump has a water pump, a compressor and a ventilator
The water pump must always be ON for the compressor and/or the ventilator authorized to run.
Push button 1 of VMBLCDWB toggles the Relay1 (pump)
Push button 2 toggles the ventilator
Ventilator relay operates the compressor with a “Momentary action”
The relay1 (pump) “Forced off when opened” the ventilator
So, it works very good, the ventilator nor the compressor run when the water pump is stopped.
The only problem is at power up or after a power failure : pushing button 2 activates the ventilator and compressor without the pump be running! The first solution I’ve found is to activate the pump then the ventilator and after that first “manual” intervention, the system works.