[dl montana]

I've been chasing a frost in the freezer problem. After changing the defrost thermistor and the control board the defrost problem seemed to be fixed, but the refrigerator side would not cool properly. There was very little air flow from the damper even though I verified the damper door was completely open. When I would open the freezer door, the air flow would improve significantly. That led me to the air return behind one of the drawers in the refrigerator side. When I looked into the return with a mirror, I saw what appears to be a piece of plastic film, almost like a piece of black plastic sheeting, covering the opening. Once I moved the film with a small screwdriver, the cooling function for the fridge side returned to normal. Now, my question is, should that piece of plastic be there, or is it something that worked its way over the opening? After moving it, when I look through the return air opening I can see the freezer evap coils. Question 2, would the lack of return air flow cause the icing problem that I origionally thought was a defrost circuit problem?