Passenger Comfort Vehicles use a Heater Core to transfer engine heat to the passenger compartment

Engine supplies the heat for the heater core

A blower moor moves air past the heater core to warm incoming air

In this picture the Fan is moving 100 cubic feet of air through the Heater Core Heat flows from hot engine parts to the colder coolant (A), past the Thermostat (B) to the , and then to the cooler air passing through the radiator (C) The heater core is built like a mini radiator

What controls the temperature of the Heater?

Some heaters have a water valve located in the heater hoses

Heater valves can be operated by vacuum, electricity or cable. Many systems DO NOT USE heater control valves Most systems use a Blend Air Door to direct and/or block air from moving though the heater core. What moves coolant through the Heater?

Convection is the main force moving coolant through the heater core Heat will always move from Hot to Cold

Water Pumps mostly move coolant through engine block and radiator.

What prevents the Heater from getting Hot?

Heater Control valves can fail. ‐ Temperature of heater hose should be hot on both sides of the valve What prevents the Heater from getting Hot? Blend air doors are moved by cable, vacuum, or electric motors. Blend air doors can get stuck. What prevents the Heater from getting Hot?

Heater cores can plug from neglected coolant Very minor contaminants can core’s Back flushing the heater core can restore heater operation. What prevents the Heater from getting Hot? Thermostats that are stuck open will keep engine coolant from warming or greatly delay how long it takes to warm up. Low coolant level will allow air to collect in top of engine and this blocks the circulation of water through the heater core

Heater cores will fail to circulate coolant any time air pockets form

Air pockets can form any time the cooling system is opened for service such as removing coolant hoses, replacing thermostat, changing Run engine to operating temperature and check coolant level, heater operation (and engine operating temperature) EACH TIME coolant system is serviced Heater Core Failure Heater cores will need replacing if they are plugged, or leaking.

Plugged heater cores will be obvious when back‐flushing (low or no water flow)

Leaking heater cores will either leak antifreeze into passenger compartment

Or out of the evaporator drain