Sounds like the temperature blend door actuator or the door itself failed. That controls the temperature of the air by directing it through the heater core or through the evaporator. If you can control the fan speed, and can control if air goes from the floor to the dash vents and to defrost but cannot control if it is hot/cold that is the problem.
I would try pulling the control head out and testing it and pray you find it is bad.
If not you will be pulling the dash assembly loose to get to the top of the heater case. The book tells you to remove the HVAC case but it is actually easier to just pull the bolts and trim out of the panel and pull it back enough to get to the actuator. No draining coolant or needing to deal with the AC charge that way.
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Tuesday, June 20th, 2017 AT 2:24 PM