Probably either fldVintage or fldSize is a text field. If so, then surround the value with quotes, like fldVintage = '1953'
e.g.
strsql = "select fldsize, fldtype, fldvintage, unitcost from qryCheckCost where fldvintage='" & Me.fldVintage & "' AND fldSize = " & Me.fldSize
I...