2009 Equinox Sport. The car is warm but, the air blows cold until the car is moving. I am assuming the thermostat is stuck until the flow is increased but, would like to verify or troubleshoot better. Any assistance is appreciated.
First thing to do is check the coolant level, low coolant, even slightly low can affect heater performance.
Thermostat stuck open would make the heater air cooler once you started down the road as the increased air flow across the radiator would cool the engine down even more.
You could have poor coolant flow through the heater core that gets better when the RPM increases. This could be a partially clogged heater core, or the vanes in the water pump could be deteriorating.