Warm Cabin Air - HCV Does Not Close Fully

2002 Tacoma w/ V6.
With air conditioning off, with the fan on and the temperature control set all they way to "Cool", the air coming through the vents is about 8-10 degF warmer than outside. Clearly some air is passing through the heater core. I'm the original owner and I suspect this has been going on for years, but has only become a problem since we moved to Phoenix.

The blend door actuator appears to be operating correctly, so I assume the problem must be with the door itself farther up inside the guts of the heating system. A shop estimated about 2 full days labor to take the dash apart to get in there. Ouch!

I've taken the heater control valve out for inspection and it opens/closes without problem - EXCEPT - that with the cabin temperature control all the way to "Cool", the valve is not quite fully closed. This seems to be by design since the lever on the HCV comes up against a stop tab before the valve gets to the fully closed position. If I remove the cable from the HCV I can tweak the valve lever to jump over the stop tab to fully close the valve. This seems like it would eliminate coolant flowing through the heater core and greatly improve the situation since I'm not wanting to dump thousands of dollars into a proper fix. I could just hook things back up normally when summer is over and the Gates of Hell are closed again. But would blocking this small amount of coolant flowing through the heater core cause other problems?

 

Pinch the heater hose off and see if it answers your question,,, it doesn't take much coolant at a 180+ deg. to disrupt the cooling of the AC.

 

I don't need to pinch the hose, I can force the valve to close fully. I'm hoping someone smarter than me can tell me if that would cause damage rather than going down the trial & error route.

 

Only thing it'll hurt is you won't have as a efficient heater in the middle of summer,

unless you torque it to hard trying to shut it off and finish off the valve by breaking it.