P38A Cruise control

I am still going through the various bits and have now come to the cruise control...…
I have replaced the piping, ECU, brake pedal switch & inverter. The old vacuum pump was working but would not fully retract the cable so I have picked up another one from our "trusty" auction site. It looks in good nick, I have tested it (pump & dump) and it fully retracts the bellows, as soon as I disconnect the test power it re-inflates. Is this normal or should it hold vacuum until the dump is activated?

cheers

https://www.dropbox.com/s/worvy52u71hcqv7/Testing CC Vac pump.pdf?dl=0

Try that, might help

That is the link I also found to test the unit/units. I am assuming after reading it again that the bellows should hold vacuum after the power is removed and remain until the dump is actuated. Hmm, all new pipes and sealed the brake line to prevent loss. I guess there must be some kind of non return valve in the actual de-compressor unit (similar to the EAS one) to prevent the vacuum escaping. Oh well, the replacement was only £20:00 so I wasn't expecting tooooo much.