I took down control cover. damper does not move from open if I adjust fridge temp control. would you suspect control or damper? I could check voltages if had schematic. any thoughts?

I am having the same problem. I have a kenmore side by side, model number: 253.51399105. I have had a repair man out for this problem twice. He is telling me that the damper door is not shutting and always seems to find it jambed. When he leaves it works fine but about an hour after he leaves I am back where I started. I have tried a couple of things. I thought that maybe while he is here that it defrosted a little and then when he closed everything back up it iced up and couldn't move. So I shut everything down for about 4 hours and sure enough the damper door would work again. Close everything up and turn up the temp and an hour later back to square one. I am thinking of taking the compressor and blowing air into the vent to maybe blow out any ice in the damper. Would you advise this or do you have another idea? Thermometer I put inside measures anywhere from 30 first thing in the am to 40 at night. What are your thoughts????