No Heat on 2001 Pontiac Grand Prix

I'm not getting any heat in the car. The a/c seems to be working fine. No overheating issues. Antifreeze is full.
Any ideas??
Thanks

2 answers
Customer Concern: No heat, both heater core hoses hot. Manual Heater Vent Air Conditioning (HVAC) system.

Tests/Procedures: 1. Test voltage backprobed at the temperature door actuator Brown wire ignition power, Yellow wire ground, Dark Blue wire control 0-12 volts. If there is a Light Blue wire it is not used.

2. Test terminal contact.

3. Remove temperature door actuator. Test for stuck temperature door.

4. Replace temperature door actuator.
Tech Tips: Temperature door actuator is located behind right side of dash behind and left of blower motor housing on end of the HVAC housing.
Bad thermostat.