Handbook 752 Air Conditioning and Climate Control PTC Heater PTC stands for positive temperature coefficient, a term that describes the electrical properties of the ceramic material in this type of heater. Because the engine’s coolant does not provide heat until the engine has warmed up, many Toyota vehicles use an electrically-powered PTC heater to provide immediate warmth on extremely cold days. Based on the voltage and current applied, the PTC heating element warms to a specific temperature. At the target temperature, its electrical properties change to maintain that temperature.
The heating unit is placed in the air stream immediately after the heater core so it can apply supplemental heat to the air when needed. The PTC heater’s heating elements are controlled by relays. When coolant temperature is low, the A/C ECU (also referred to as the A/C Amplifier) can activate one or more of the relays to provide supplemental cabin heating. Heat Ranges The PTC heater in some Toyota vehicles has three heat ranges that are applied based on engine coolant temperature, ambient temperature, engine speed, air mix setting and electrical load. Some vehicles have an additional PTC heater installed in an air duct of the blower housing.
This additional PTC heater helps increase the air temperature in the ducting. Technical Training 11