HiCustomer Thank you for asking your question on JustAnswer.
With the engine at full operating temperature are both heater hoses hot? You should not be able to hold them more than 5-10 seconds without having to let go.
If both hoses are hot then there is a problem with the temperature blend door or actuator in the heater case. The blend door actuator will need to be removed and checked for functionality to see if it turns when commanded with the temperature switch. If it turns then the control side is OK and the actuator will need to be checked under load for stripped teeth and the blend door will need to be checked for binding or possible broken actuator connection point. If it does not turn then the electrical portion of the system will need to be tested to verify there is proper voltages for the command and feedback circuits between the temp switch and the actuator. The actuator is somewhat difficult to access, the passenger airbag needs to be removed as well as the defroster duct trim and keyless entry module. Click the links below for access instructions.