Hi; 1999 ford e-250 cargo van with heat problem. Replaced passenger side heater damper motor. Motor run, but still wants damper to be in 1/2 heat & 1/2 cool. Is there anything else a regular driveway mechanic can do to fix the problem?

Optional Information:
1999 E-250 cargo van van 5.4L

Already Tried:
replace heater damper motor