Congrats on the purchase.
3 Things.
#1) Fix the freon leak, get a can of dye and a black uv light to find out where the 134a is coming out(usually the compressor or the the schrader valves)
#2) Does the car temp gauge works, and if it does, do you reach normal operating temps? If that is a yes too, check the heater valve to see if it is disconnected/not working).
The heater valve works via vacuum and motorized actuators by the passenger side of the heater motor/core body with multiple vacuum hoses T-ing off and connecting to other actuators that will create a vacuum when your temp control knob is twisted to heat or cool the passengers of the vehicle.
With that said, the heater valve is located right behind the intake manifold, near the firewall, it's plastic and should have 2 rubber hoses running from the back of the head to the valve, then from the valve to the heater core. There should also be a hard plastic line running to it for vacuum to operate the opening and closing of the unit, verify that is on and not causing a vacuum leak.
Once that heater valve has vacuum, it opens and heated coolant will run through the heater core and produce heat.
You can always remove the vacuum line and by hand, move the lever open and you should then start feeling heat in the cabin, and reinstall the vacuum line once tested.
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/359171-im-confused-heater-valve.html
#3) Broken heater clips
https://rennlist.com/forums/924-931-944-951-968-forum/515482-broken-heater-clip-hot-air-blowing.html
Report your finding to us in this forum, and we can help you from what you find out.