Weather has been cold below freezing, which when turning on the heater even on high only blows cold air. Had heater serviced/fixed three years ago for hefty fee. Which part(s) would have to be replaced and how difficult of a procedure?
My car has an automatic transmission.
The lack of heat being generated by your system may indicate a clogged heater core. The [heater core]((https://www.yourmechanic.com/services/heater-is-not-working-inspection) is a small radiator like unit that circulates the hot coolant from the engine through the heater core which then uses this warm coolant to heat the inside of the car with the help of the blower motor that blows the warm air through the vents inside the car. The other possibility is that the thermostat may not be allowing the engine to reach a normal operating temperature and since the engine’s warm coolant is the essential source of the heater core supplying heat to the inside of the vehicle, this can impact the warmth of the heat inside the vehicle. I would suggest having an expert from YourMechanic come to your location to diagnose your heating system.
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