Over this winter noticed exhaust fan in microwave did not seam to be doing anything.Checked from outside and flapper on vent at back of micro was not coming open.Seamed to be blocked.Waited till home and pulled micro. vent was to low for opening in camper.Trimmed about 1/4" from top of vent adpter on mico slid vent up in attachment.Taped and screwed in place.Works fine now.Not sure if something moved or was allways this way.