Well, I hate to tell anyone to go ahead without a good diagnosis unless I'm really 100% sure, at least 90% sure. i'm only about 75% sure in this case. the aux pump is possibly bad, but you should still have adequate heat without that working. The power and ground shouldn't have any effect due to the failsafe mode i mentioned before. Low coolant I'm sure you would have noticed, that of course is a possibility on all cars with a heater using the engine coolant (liquid) for heat. Maybe a flap problem in the heater case, but not really common. The heater core will usually way overpower the evaporator section of the A/C, so I don't think it's a failure of that nature.
One thing bothers me, and that's that this isn't a real mono-valve, it's a duovalve, that's why you have driver and passenger settings for the heat. It seems liekit would have to be a dual failure of the valve, both sides went bad, unless there is something that can fail that would affect both sides, but I don't think there is. Another problem I see is that these hardly ever fail. I know I have replaced them before, been so long I can't remember what for.
As a final test, get the engine warmed up and run the defroster, then check to see if the hoses that run to the interior are getting hot or warm at all. The engine side hose should get a little warm, even without good flow through the valves. You could also take the hose off coming from the engine to check for some (?) kind of obstruction, also check the return hoses for any kind of kink in it which may obstruct flow.
Gilly

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