How a Car Heater Works

Typical Car heater system

Before trying to fix your car's heater,  you should understand how your car  heater system works. On this page, an explanation  of how your car  heater system functions, and then, further down, some pointers  on heater system troubleshooting. A car heater is designed to warm the passenger  cabin of your car; this system makes use of excess heat from theengine's internal combustion process.  A car's Engine , in fact, when in operation produces so much excess heat that if  excess heat is not removed, it would destroy the engine. It is your car's cooling  system that removes the excess heat; some of an engine's excess heat is released  through the exhaust system.

Most of the rest of an engine's excess heat is absorbed by a circulating liquidcoolant, a mix of water and antifreeze.  The heated liquid coolant is carried from the engine through the hoses to theradiator, which transfers the heat  from the coolant to the outside air through a convection process. The heater core  in your car is similar to the radiator in the front of your car; in fact it looks  like a small radiator. The difference is the heater is mounted inside the car and  air is blown through the fins of the core. The heater hoses transfer engine coolant  to the heater core, this allows the heat from the engine coolant to be utilized  and warm the passenger compartment air.

The heat transferred lowers the temperature of the liquid coolant, which is then  circulated back to the engine to absorb excess heat again, a continuous system.  Whereas the radiator is located at your car's front grill, the unit that transfers  heat to the passenger cabin (heater core) is located inside the dashboard near theair cabin filter. This  unit, something of a mini-radiator, is referred to as the heater core. Heated liquid  coolant circulates through tubes in the heater core, and a heater fan blowing across  those tubes, as well as through little fins encasing the tubes, directs warmth through  the heating vents into your car's passenger cabin.

Heater Problems

Because your car's heating system works off of thecooling system, sometimes,  heating system malfunctions are caused by problems in the cooling system. One of  the first things to check when your car heater is not working is yourengine coolant level. If your car  has a coolant leak in the cooling  system, the heater will not be able to produce adequate heat. In any event, to keep  your car running optimally, you should regularly check the coolant level. For saftey  reasons, this absolutely must be done only when the engine is completely cooled  down. This safety point cannot be over-emphasized.

Opening the cooling system of a hot engine presents a terrible burn hazard, as  the fluid in your car's cooling system is dangerously hot and pressurized when the  car has been in operation. It is best to let the car cool overnight before inspecting  the coolant level. Most cars have coolant reservoirs with opaque white plastic tanks  and measuring lines allowing you to see if the coolant is at the recommended level.  Coolant expands when heated, and for that reason, most coolant reservoirs have a  Full-Cold and a Full-Hot line.

If there is too little coolant in the reservoir, you should be alert to the possibility  that there could be a leak somewhere  in your car's cooling system, but you may nonetheless remove the reservoir cap and  add coolant to the Full-Cold line. Obviously, if a very short time after you refill  the coolant reservoir, the coolant level is low, there is a leak in your car's cooling  system. Many points in your car's cooling system are liable to develop leaks through  which coolant can escape. Too little coolant in the cooling system will result in  a malfunctioning heater. To inspect for a leak in your car's cooling system, you  should understand that the main physical components involved in the cooling system:

• Engine block
• Thermostat
• Upper and Lower Hoses
• Radiator
• Radiator Cap
• Radiator Fan
• Water Pump
• Heater Core
• Heater Hoses
• Heater Blower Fan Motor

A leak in the heater core occurs most often in escaped coolant on the front passenger-side  floor of the passenger cabin. Most Car antifreezes are either green or red,  though they might also be another color, and that despite a sweet smell they are  toxic and should never be ingested. Particular care must be taken to dispose of  used coolant properly, as the sweet smell can attract children and pets, and disposing  of used coolant at random contaminates the environment. The best way to repair a  leaking heater core is to replace the core. Even more common than a leaking heater  core, however, are leaking heater core hoses.

Car Heater Hoses

The heater hoses are held in place by spring loaded hose clamps and can be removed  with the proper tool. Visible signs of leakage are the most obvious indicator of  heater hose leaks, but you should also physically inspect the hoses for signs of  deterioration. Squeezing one hose at a time, you should feel that the hose is soft  and flexible. There should not be any irregular bulges in the hoses. You should  not feel any dry rot, which manifests as brittleness and/or cracking or weaknesses  in the hoses. If you detect any of these conditions the hoses must be replaced.  Consult your owner's manual orservice manual,  as it will likely have details specific to your car's heating system.

Before you replace any hoses measure the length and diameter of your old hoses  so you will know the size your new ones must be. Many cars use three different sizes  of heater hoses; the standard diameters are 1/2", 5/8" and 3/4". When removing the  old hoses, take care not to use any yanking or turning motion that could damage  the heater core. Repair technicians often score the old hoses open with a blade  and then gradually coax them loose before removing them.

Controlling the heater system varies in most cars, but primarily there are two  designs, the first design is the "manual control system", which constantly requires  manual adjustment from the driver to maintain the desired temperature. And the automatic  temperature control system which is a computerized management system, this system  can keep the cabin at a selected temperature or split the set temperature from the  driver or passenger side compartments. When a heater core fails it can leak coolant  inside the car on the driver or passenger side floor board. Replacing a heater core  is different on every vehicle, for the exact procedure on your particular car consult  a repair manual.

Replacement can vary from undoing 5 screws and replace it, to the " they  started with the heater core, then, built the rest of the car" kind of job which  removing the entire dash is not unheard of and can take many hours. A heater control  valve is used to stop the coolant from flowing into the heater core when the heater  system is off or the air conditioner is turned on. When the engine is cold the heater  will not work a heater core must have heated engine coolant to work.

Common Problems

• When a vehicle is low on coolant it can cause the heater to stop functioning.
• When the car is running you can hear bubbles flowing through the heater core, (like a fish tank) this is due to air becoming trapped inside the heater core, in time the air should dissipate to silence the noise.