AC Voltage Regulator for Motor

For my CNC mill I've bought an ash vacuum cleaner.

I've found a lot of people who made their own Dyson Cyclone vacuum cleaner.

When I finally have my CNC, I'll convert my ash vaccum to a cyclone vacuum. :)

But now to the ash vacuum cleaner...

As I turned it on the first time, I thought "woooow, I'm standing behind a starting jet plane!!".

It's really loud and has insane power (I think about 2000W). There's only one switch for turning it on or off. 

So I start to search something to regulate the power and found a regulator on ebay.

I also bought a netfilter with 2 fuses, a main switch, plug socket, a LCD display with volt/amp meter and last but not least - a nice case.

It was the first time I didn't made a plan at the computer and check the arrangemet of the components digitally. 

I took the case placed the components on it and thought "this will work".

I applied a wide tape on the case and drawed the pattern of the components on it.

Cutted them out

Inserted the components, made the wiring and attached power to it.

The box is working fine. I can regulate between 36-230VAC.
Except when there's no load, the display shows strange values or does not even work...
Think this is because of the regulator...

Mental Note:
I'm not going to trust this device fully, because of the ac regulator bought on ebay... You never know how good the quality is and you have no certificates of that component.
So I'll not use this device unattended.