Heater suction control valve faulty

[Only4Wheels]

Hi,

The heater in my Ford Transit 1997 Turbo Diesel van was not blowing hot air.
I located the valve that directs the hot water to the heater core. Removing the suction line to this valve caused it to operate, the actuator extended and hot air flowed.
The valve is controlled by another unit. I don't know its name but I'll call it a vacuum control valve. The heater control supplies 12v to the vacuum control when cold is selected and 0v when set to hot.
When it is faulty, tapping the vacuum control value causes it to operate so I suspect the issue is with a sticking unit. Does anyone know the proper name and is there any way to service it?

[Only4Wheels]

Here is a picture of the unit

[Only4Wheels]

In case this helps anyone else. I removed it and took off the top cap turned iit upside down and gave it a few taps. It seems to be working now. If it fails again. I may spray sone brake cleaner (I'm told it leaves no residue) in the hole which I assume an armiture is travelling in.