How does the U. Plenum Water heater work?

[nfsdave]

From a picture, it looks like there is an electrical connection that controls it. What gives it a signal - outside temp.? I'm told that it doesn't operate in the warmer months. True? The reason I ask is that the top Motordyne plenum spacer kit has a copper heating unit and implies that this replaces the OEM heater. I'm always suspicious of electrical add ons that look cheap. Thanks