So I think I finally determined is that my problem with no heat was due to a sticking heater control valve. When I took it out of the car, I noticed it would just lock in a closed position for an indeterminate length of time and then pop open.
I have two other heater control valves that seem to operate fine, but when they're in the closed position, they seem to leak just a little tiny bit when I blow on the valve.
I'm trying to decide if this bit of blow by would be acceptable, or should I try and Source in new rebuilt one? Unfortunately a rebuilt one would be pricey.
Thoughts?
Bill M