Thanks for all the responses... the culprit here was a huge amount of
calcium buildup and corrision... the two bad loop's manifold valves
were completely eaten apart, that is, the shaft was no long connected
to the closing seal... so, up or down, nothing was happening as far as
opening or closing the circuit. Should have checked that earlier, but
this was a new manifold installed just 8 months ago.
That solved, the question remains as to why so very much corrosion in
such a short period of time...????