Welcome to the Board.
I had the same issue with Air recyling function, it was not working. It was a POD (vacuum element), the recycling funciton pods (2 of them) are located right behind your glove compartment. You have to take the glove compartment out to access them. They open and close a big rectangular door on top of the blower motor. The diaphram could have been reptured on these pods, these are douple stage PODS ~$40 a piece.
As for as the heat to the floor vent is concern that is also another pod on the side of the center console, I believe it is on passanger side and it is a single stage pod ~ $25.00.

It is not a bad idea to check the vacuum system with mity vac, it could be as simple as lose vacuum hoses to the pods or as complex as 7 port vacuum control unit behind the dash.

If I were you I will take the glove compartment out first and check the vacuum connection (2 on each pod) to the recyl POD first, then do the mity vac test, and folow the leak.

Good luck and keep us posted.

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87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)