Laverne and Shirley: The Haunted House (1977)

The gang heads to an old abandoned house in which Carmine informs the girls they could pick up a couch for free. But their friends seem to disappear one by one while inside the haunted mansion. (Synopsis from ShareTV.org) Originally aired March 22, 1977.

The episode isn't readily available online, but here's a recap and analysis from the Night After Night Podcast: