Central vac turns on randomly, but mostly just stays off if it's off, or stays on if it's on.
There is a 24v low current transformer that energizes a sense circuit at each outlet of the central vac. Plugging in to the outlet shorts the circuit causing voltage to drop to near 0v, triggering the vac to turn on.
In my mind, the 24v holds open a normally closed SPST relay, preventing the vac from running. Shorting the 24v allows the relay to close and turns the vac on.
The simple stinkin board costs $145. I'm thinking either the relay, or the transformer is the culprit (there isn't much else on the board). How do I test this, or should I just throw a $5 relay at it and see if that fixes it?
This dumb part should be like $20. Also, the failure mode shouldn't be "run". Also, it shouldn't fail.