A/C works, Blower Works, No Heat. Where should we start?

Let the engine warm up. What is the temp reading on your temp gage, in degrees F? I consider 210--220 degrees f, a warmed up engine. I realize the temp may vary a little from one vehicle to the next, but, you get the general idea. You may have to check your thermostat? also, with warm engine, feel of heater hoses, are they warm or hot? The hoses should be on the firewall, under the hood. If so, maybe problem with temp actuator or control. Any applicable hvac trouble codes?

Check the coolant level and purge air out of the system.

Would most likely be your actuator. The unit that switches the air coming in from hot to cold. Check YouTube videos on where it is located and several possible DIY fixes.