With the car hot, feel both heater hoses. One hot, one cold means clog. If both are hot, it's a blend door issue. Clogged core is the likely culprit. Flush it gently in both directions, refill, then carefully bleed the system using the bleeder on the top of the thermostat housing. Helps to have the nose up a little. Ramps or a sloped driveway will be good.
Two doors, four doors, wagons, and ragtops.