defrost not working

[gramps77]

After finding a cracked vacuum line going into the firewall, I was able to get my vents to transition again from vent to heater but defrost is not working. How many lines are there in the system and where else should I be looking.
The vent pointing down for heater selection and then dash vents transition just fine and its very obvious. Defrost simply just never happens.
I realize we are going into summer, but after my dash replacement, Id like to button it all back up with it all working