Method for controlling electric heater of vehicular HVAC system

A method for controlling an electric heater of a vehicular heating, ventilation, and air conditioning (HVAC) system, the method comprising:

• turning on, by a controller, the electric heater;
• determining whether an ambient air temperature of a vehicle is higher than or equal to a threshold ambient air temperature, and a battery temperature is lower than or equal to a threshold battery temperature;
• determining whether battery efficiency is lower than or equal to threshold efficiency;
• and
• turning off the electric heater when the battery efficiency is lower than or equal to the threshold efficiency, and keeping the electric heater on when the battery efficiency is not lower than or equal to the threshold efficiency;
• wherein the electric heater is configured to receive electric energy from the battery;
• and
• wherein determining whether the battery efficiency is lower than or equal to the threshold efficiency comprises comparing the battery temperature with a plurality of reference temperatures and comparing an instantaneous discharge current of the battery with a plurality of reference discharge currents.