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Q: Heater blows cold when temp gauge is halfway. both heater core hoses are hot.

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the Haynes manual mentions a heater control valve but does not show a photo of it, or where it is located. Will it blow hot air if it has not been bled off? Manual mentions bleeding off the cooling system. What does this have to do with heater working? I live in the southwestern Sonoran desert so the heater does not get used a lot.

My car has 100000 miles.
My car has an automatic transmission.

If both heater hoses are hot then the core is getting hot coolant flowing through it. You should check the temperature blend door actuator behind the glove box on heater case to see if it is operating the temperature blend door or not. If the actuator is not moving then replace actuator and retest the heater output.

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