I have no heat. on 2000 Dodge Grand Caravan

I replaced the thermostat, and still nothing, coolant is topped off, someone said something about a valve on on the firewall that might be stuck open. At this point my mind is boggled. any help would be much appreciated.

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2 answers
You have a broke blend door. You have no valve at the firewall. The blend door is in the HVAC box. Not a inexpensive repair.
caravans are well known for the climate control to go out.
does it switch over to cold air?