If your car heater is not working as well as it used to or has stopped working completely, it may be due to a plugged core. The heater core is similar to a radiator, and is a part of the vehicle's cooling system. Hot coolant that passes through other parts of the engine passes through the heater core as air passes through the heater and into the cabin to warm the vehicle. A clogged core prevents coolant from passing through it, thus limiting the amount of heat it can transfer. Cleaning the core removes these clogs, but if it doesn't work, you may need to replace it with a new one.
Part 1 of 3: Fix a Pressure Source
Step 1. Find the heater core in the car's firewall
The heater core inlet and outlet tubes are generally located in the firewall, separating the engine from the vehicle cabin. Their location varies from vehicle to vehicle, so if you can't find the inlet and outlet hoses, read the service manual for your specific car.
- There are two nozzles, one for the coolant flow in and one for the flow out.
- Follow the coolant hoses through the cooling system to find the nozzles.
Step 2. Disconnect the hoses from the heater
Coolant hoses are usually attached with hose clamps that are loosened with a screwdriver or wrench. Remember that when you disconnect the hose from the heater, the water and coolant will come out of it, so be sure to place a container just below the hoses, under the car.
- If you damage the hose clamp while loosening it, you can buy replacement parts at your local auto parts stores.
- Be careful not to splash coolant on the floor, as it is harmful to the environment.
Step 3. Point the inlet hose toward the container
To clear the blockage in the heater core, you will have to force air or water through the system. When you do, the coolant, water, and dirt inside the system will come out through the inlet hose.
Make sure the hose is well positioned so that everything that comes out falls into the container
Step 4. Insert a water or air hose into the outlet hose
If you have an air compressor, you can use air to remove the remaining coolant and dirt inside the heater core. Otherwise, you can use a garden hose for the same purpose. Attach the hose or air source to the outlet hose from the heater core.
You will still have to use the water hose to clean the system, but the air compressor has more force to break through the clogs
Step 5. Seal the line
Strive to seal the line at the connection between the hose or the air line with the outlet of the heater core. Wrap the area with tape or use silicone clips; both options are effective in creating the seal.
- If there is a major blockage in the line, the pressure could rupture and leak the hose back, instead of penetrating the blockage.
- A good seal around the hose pushing air or water through the system will force the pressure to point to the clog.
Part 2 of 3: Drain Dirt and Coolant
Step 1. Turn on the hose or air compressor
Turn on the air or water with the air source or sealed hose as far as you can at the outlet of the heater hose. Allows pressure to enter the system to remove obstructions. Coolant and dirt will drain from the heater inlet into the container below the vehicle.
Leave the hose or air source on for a few minutes to make sure it pressurizes the entire system
Step 2. Allow the coolant and dirt to drain
Turn off the air source or water hose and allow the fluids to finish draining into the container you have placed under the car. Make sure the container doesn't overflow if you use a hose.
The system may continue to drain for a few minutes after the air or water flow is turned off
Step 3. Repeat the process with the water hose
If you used an air source to remove the initial clog, you should now use a hose and repeat the process. Filling the system with water and allowing it to drain will remove the bad coolant.
- You can pour the liquids into a separate airtight container between cleanings to make sure it doesn't overflow.
- Clean the system one or two more times before proceeding further.
Step 4. Reconnect the inlet and outlet hoses
Place the heater inlet and outlet hoses on the nozzles and secure with the clamps. This will reseal the system and allow it to refill. Make sure to secure the clamps well. Otherwise, the water pressure will cause the hoses to come off.
- Replace any broken or rusted clamps before reinstalling the hoses.
- Hoses generally only go to one nozzle, so it's easy to determine which one goes where.
Step 5. Fill the cooling system
Open the radiator cap and fill the cooling system with a mixture of 50% water and 50% coolant. Make sure you use the correct type of coolant for your car. Once you fill the system to capacity, screw the radiator cap back in place.
- You can buy a coolant and water premix or make your own mix.
- If you don't know what type of coolant is right for your car, ask a salesperson at your local auto parts store for help.
Part 3 of 3: Prepare to Clean the Heater Core
Step 1. Park the vehicle on level ground
You should never jack up a vehicle on an inclined surface. Otherwise, the cat could fall. Find a firm, level surface that can support the weight of the front of the car once it is centered on the jack.
- Asphalt concrete and concrete are the best surfaces to jack up a car.
- Never lift a car on grass, dirt, or gravel.
Step 2. Allow the engine to cool completely
The cooling system is pressurized when it heats up, so loosening or disconnecting the heater core hoses while the engine is hot can cause it to spray hot coolant and injure you. Wait a few hours after the engine was last running before starting this project.
- Run your hand over the hood of the car. If it is just warm, the engine is probably very hot.
- It may take several hours for the engine to cool down completely.
Step 3. Raise the vehicle
Slide a forklift or scissor jack under the car at one of its designated spots. Raise and lower the lever (forklift jack) or turn (scissor jack) to lift the car.
- If you don't know where to find the designated points on the car, read the owner's manual for more information.
- Once the vehicle is raised, slide the jack stands under to support the weight of the vehicle.
Step 4. Place a container under the vehicle for the drained fluids
You will need to clean all the coolant and debris from the heater core and part of the cooling system in a container on the floor. Make sure the container can hold at least the capacity of the vehicle's cooling system.
- Read your vehicle's service manual to determine its coolant capacity.
- Make sure the container you use is leak-free and preferably sealable to transport the coolant to a recycling center.