Vehicle at running temp, turn on heat, no heat – stomp on gas, there is heat – ??? 2004 Jeep Liberty

When I turn my Jeep on and let it get to normal running temperature I turn on the heat it blows cold air I stomp on the gas there's Heat let off the gas it goes back to cold air what could be the problem

My car has 104000 miles.
My car has an automatic transmission.

– Vehicle at running temp, turn on heat, no heat