It was a small shut off sol valve that was being controlled by an electronics board - opening and closing to feed small amounts of refrigerant to the head. Seems like the head must have some sort of temp sensor in there but as it was sealed up we couldn't really see.

This is the sort of thing I mean http://www.fluesystems.com/pipe_free...nfo/arctic.htm

Seems suitable for this overclocking use as the refrigerant appears to be metered to suit the load.

Frank