The climate control is no longer working in my parent's 83 300D. Is it possible to swap it with the unit from a 1985 300TD (the dead car)?

The unit in the 300D does nothing. No fan, etc. The car has a new heater fan put in last winter. Anything else that I should look for?

Thanks in advance.

__________________
Paul

1991 300TE (280,000)
1985 300TD (432,000 miles - retired)
1976 300D (225,000 - retired)
1975 300D (165,000 - retired)