Q: The A/C in my car worksand the air blows, but will not switch to heat

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I can turn the A/C on and turn the dial to heater temperature, and the heater will not work.

My car has 75000 miles.
My car has an automatic transmission.

If there is no, or little heat, typically that means that either the heater control valve, located in engine compartment around the firewall, is not functioning, the heater core is plugged, causing lack of flow of heated coolant through the core, and/or the blend door in the ventilation network under the dash is not switching to allow air to blow over the heater core versus blowing over the a/c evaporator. But, you should also check for low coolant level because that can cause this issue, too. The control valve can typically be ruled in or out based on a visual inspection of position. Blockage might be inferred by comparing the temperature of the inlet hose to the heater core versus the outlet hose. If valve is OK and coolant is flowing, that means the blend door is malfunctioning. I would recommend you request a no heat diagnostic during which a certified Mechanic will identify the root cause of the problem and explain the required repair and the cost.

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