No, if you have voltage at the monovalve, the PushButton Control Unit (PBCU) is fine, the solenoid is bad.
The monovalve is held closed by current flowing through the coil, it opens when no current is present. If it is opening with voltage (meaning you have water going through, and hot air coming out the vents), the solenoid is bad or the valve is sticking.
Make sure the spacers are correctly installed, the same way they came out, and that the coil is dry and clean. Sometimes when the monovalve diaphram leaks, you get corrosion in the coil chamber, so the armature can't move properly, so it stays open.
Check for continuity across the pins, too -- if you have an open circuit, you will need to replace the coil.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!