Outside Cold Air Return on Furnace A/C

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We just purchased a home built in 2003.  One thing we found that I have never seen before is a 8" return air duct work that comes from the outside of the house to the main truck on the return side of the heating A/C unit.  The duct work does have a manual damper which I closed for the time being.  From what I understand, this is to supply fresh air to house.

1.)  When should the damper be open?  All year around - summer and winter?  Should the damper be slighy open?

2.)  Also I found a timer on the side of the heating and A/C unit  (ones where you would use on christmas lights).  Im not sure what this timer is for.  

Thanks   John from Ridgefield Washington.  

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