At what engine coolant temperature can the heater be turned on?

[DelLillian]

You can turn on the heater when the engine coolant temperature reaches 80 to 90 degrees Celsius. The car's air conditioning system relies on the heat from the engine coolant to produce warm air. The air conditioning is an important comfort feature in a car, capable of both cooling and heating, and is used almost daily during winter and summer. When the air conditioning is in heating mode, the hot coolant from the engine flows through the heater core. At this time, the air blown by the blower also passes through the heater core, allowing the air conditioning vents to blow warm air. When the air conditioning is in cooling mode, the compressor clutch engages, enabling the engine to drive the compressor. The compressor continuously compresses the refrigerant and delivers it to the evaporator. Inside the evaporator, the refrigerant expands and absorbs heat, cooling the evaporator. The cooled evaporator then cools the air blown by the blower, allowing the air conditioning vents to blow cold air.