2002 Sierra Heater Problems

[Daniel.]

I own a 2002 Sierra. Since last year I notice that it is colder at the floor level on the passengers side. There is a lot of heat comming out of the ducts on both side but the heater assembly under the dash on the passengers side is very cold to the touch. I seem to think that a damper is not closing properly inside the heater assembly. Can somebody help me with this problem.