The primary components of an automotive heating system are the heater core, the heater control valve, and the blower motor or the fan. These three items work together and push warm dry air out of three different destinations.
These are the vent ducts that point to the driver and passengers the defroster ducks that point towards the inside surface of the glass and a floor heater duct that usually points down towards the carpet or flooring.
The heater duct is mounted low and pointed down because hot air rises. When the warm air is released at its lowest point possible it will then rise towards the headliner and warm the interior compartment on its way up.
How the heating system works
As the coolant circulates through the heater core this heat is transferred from the engine coolant to the tubes and then the fins of the heater core itself. This is very similar to the automotive radiator that is mounted in the front of the vehicle. Air is then blown through the core by the blower motor where it then picks up the heat from the surfaces of the thin metal fins that make up the heater core.
It transfers the heat to the passenger compartment by blowing it through the duct work that was described above. After the heat is removed from the coolant it is circulated out of the heater core through the outlet where it is returned to the engine to be re-circulated by the water pump and reheated.
Heater core problems
Overall heater core problems are generally caused by leakage or clogging. Depending on the location of the heater core often the first signs of a leak would be engine coolant collecting on the passenger side floor. Another telltale sign that your heater core is leaking is a sweet smelling aroma when the heater is turned on.
Another indication of heater core problems would be that the ability to remove fog from the inside of the windshield has been reduced. If the blower motor is picking up coolant and blowing it on the inside of the windshield it will not be effective at removing fog. Sometimes when this happens the driver's complaint is a constantly dirty sticky windshield.
A sign of a block heater core would be a driver's complaint of no heat output. You can check for a blockage by checking the temperature of the inlet hose and comparing it to the temperature of the outlet hose. If the inlet is very hot and the outlet is cool this would be a sign that no flow is passing through the heater core.
In some cases when a heater core is blocked it can be reversed flushed to clear the blockage. Often this will just buy you some time because a blocked heater core is a sign of interior corrosion and will eventually need to be replaced. I have another article that covers some additional automotive heating system problems. Or visit this next link for more of the latest posts to the blog for auto repair.