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Engine Coolant Level
Heater Hoses
Heater Box
Gaskets and Seals
The Heater Core
The Blower Motor
Heater Control Valve
Select a part to view solution for common problems associated with the item.
Advice: The efficiency of the heating system is dependant on a full cooling system. A small leak anywhere in the cooling system can cause the heater core to be dry long before you notice any kind of overheating problems. A dry heater core is not going to give off any heat. When dealing with a heater that is not heating, before replacing any parts, ensure that the coolant level is full.
Operation: The heater hoses carry the hot engine coolant to and from the heater core. Advice: One of the first things to do when replacing the heater core is to disconnect the inlet and outlet heater hoses. These hoses are often hard to get to on the firewall behind the engine. Some v6 engines are designed to rock forward after disconnecting the engine torque struts to give you better access to the back spark plugs. Using this technique will give you better access to the heater hoses as well. Check the repair guides for the vehicle that you are working on. Recommendations: Repair guides
Operation: The heater box houses the heater core as well as blend doors and blend door actuators. On AC equipped vehicles the AC evaporator is also housed in the heater box. Advice: The most difficult part of a heater core job is gaining access to the heater core. Most likely, the area you will be working in will be cramped under the dash and it will seem like there are 100 screws holding the box together, half of them hidden from view. Take your time and don't get frustrated. An exploded view diagram showing the location of all of the mounting screws is worth it's weight in gold at this point. Check the repair guides for the vehicle that you are working on. Recommendations: Repair guides
Operation: Inside of the heater box there will be several gaskets and seals that are designed to direct the airflow across the heater core and/or AC evaporator. Advice: Pay close attention to the condition and placement of the seals and gaskets inside the heater box. Most of the time they can be reused, but failure to place them properly or replace them if necessary will have a negative impact on the efficiency of the unit.
Operation: The heater core is responsible for radiating the heat from the engine coolant passing through it to the air being forced over it by the blower motor. Advice: The orientation, size and length of the heater core and the inlet and outlet tubes is critical to the heater core fitting properly into the heater box. Carefully compare the new heater core to the old one before attempting installation. Some replacement heater cores come with plastic inlet and outlet tubes. Use care not to crack them during installation.
Operation: Engine coolant is a 50/50 mixture of antifreeze and water. Besides protecting against freezing, antifreeze also has lubricant and anticorrosive additives that help to prolong the life of the cooling system components. Advice: Most heater core replacements take place due to a leak in the heater core. A leaking heater core is usually due to corrosion. Corrosion in the cooling system is usually due to worn out antifreeze. The ingredients in antifreeze that protect against freezing are pretty much permanent, but the lubricants and anticorrosive wear out over time. Most manufacturers recommend flushing the cooling system and refilling with fresh coolant every two years. Some manufacturers recommend a specific type of antifreeze, such as GM's Dex-cool. Check the repair guides for the vehicle that you are working on. Recommendations: Repair guides Antifreeze
Operation: The blower motor is responsible for driving the fan that blows air across the heater core. Advice: If the blower motor is not working, first you must determine if the blower motor is at fault or if the problem lies in the speed control circuit and/or wiring. One of the quickest ways (depending on accessibility) to test a blower motor, is to hot wire it. If you disconnect the wiring harness and apply battery voltage to the blower motor terminals and it does not spin, then you know that the motor is bad. If it spins, you know the problem is somewhere else in the system. Most blower motors will have two wires or terminals, a positive and a ground. Check the repair guide's wiring diagrams to determine which is which. If you do get it backwards, don't worry. Reverse polarity will only cause the motor to run backwards. For testing purposes, if the motor spins in either direction, the problem lies elsewhere. The one wire design gets it's ground through the blower motor mounting, so the single wire or terminal is your positive connection. Recommendations: Repair guides
Operation: The heater control valve regulates the flow of engine coolant through the heater core. In older vehicles it was used along with some simple blend door manipulation to moderate the temperature inside the vehicle. On modern vehicles engine coolant flows constantly through the heater core and temperature is controlled through an elaborate blend door system. If a heater control valve is found on a modern vehicle, it's purpose would be to shut down coolant flow during the summer months for maximum air conditioning system efficiency. Advice: If the vehicle that you are working on has a heater control valve, it will be installed in one of the heater hoses. Not all cars have a heater control valve. Locate the heater hoses and follow along their lengths. If you do not find a heater control valve, don't worry. Most modern vehicles Use blend doors in the heater box to turn the heat on and off.
*This image does not represent the actual look of your selected vehicle. Please refer to any car manual to see specific part.