Honda Repair: Honda Accord Heating/AC problem, honda accord, water valve

Question
I have a 2000 Honda Accord. Recently, it has been getting "stuck" in heating or
air conditioning mode, regardless of the thermostat setting.  I can change the
fan speed by adjusting the thermostat, but I can' t change the temperature of
the air. Some days I get only hot air, other days I get only AC. The air keeps
flowing,  even when the system is turned completely off. My dealer has not been
able to "duplicate" the problem, since it does occasionally work correctly.
I feel there must be a damper door or a cable that gets stuck.  Any ideas?  

Answer
Cindy, I would suggest removing the water valve which is located at the firewall under the hood. You'll see a water hose going into it and one coming out and a cable which controls whether or not coolant flows to the heater core. I've seen the valves fail internally so operate it out of the vehicle and watch inside the valve and see if the door moves smoothly and free. From looking at it work in the vehicle it'll look fine. Try that and let me know, RICK