Modesto came back this morning. We were still getting 1 hot blower and 1 cold blower.
As it turned out, although hot water was reaching the south heating coils input, it was not getting into the actual heating duct (as we could tell from touching those coils).
Modesto tapped the actuation valve with a hammer and it seemed to loosen it up. We will record temperature over the weekend.
Also we noted that the damper valve near the south-east vent was adjustable, but had no effect on the output air velocity so we assume its busted inside - Modesto will crack it open to investigate.
We also reduced the flow of hot water to the north blowers since they always seemed to be hotter. This may balance the actuators somewhat.
Modesto also replaced the thermostat on the west wall, but no real effect. I have adjusted the setpoint from 74 to 71F around 1800 today.