vent/blower malfunction

Ive read several threads in here for the vent/defrost blower moving around within the cab no matter where it is set. I have 96 ram with same problem. All threads say to check vaccuum lines but has anyone figured out the area in which to check. I have already done the under the battery one for the air/cruise to get that working but am at a loss for the blower malfunction. Thanx in advance for any help

most of the vac lines in question will be behind the dash, connected to the vacume switch, which is directly behind the nob that you turn to select which vents are blowing. also, you could check the vac supply line that goes from the intake manifold, through the firewall, and then to the vac switch. also, there is a check valve located in the main vac line (the one that goes to the switch). if I remember correctly, it's located under the hood, before the vac line goes through the firewall.
the dealer should have an upgraded check valve available.

purchased the check valve, and had it installed. there was no check valve in the system and had to be added. 30 SECOND JOB ADDING IT IN BEFORE THE VACCUUM LINE WENT THRU THE FIREWALL. Working fine now.