Hyundai Sonata Heater Won't Workby TJ Hinton
Your 2013 Hyundai Sonata is equipped with a cabin filter located behind the glove compartment liner. Return air from the cabin passes through this element, which is designed to remove dust particles and foul odors from the cabin air. If you find that your heater performance drops off when using the "Recirculation" function on your climate-control panel, remove the liner and clean or replace the cabin filter.
Failures in the blower, blower control and associated wiring are common. Before checking the blower itself, check the blower circuit fuse and relay. If the relay is bad, replace it. However, if the fuse is bad, you also need to check the blower resistor, blower motor and associated wiring. While fuses can sometimes fail because of use and vibration, a blown fuse can also signal problems in the blower or insulation breakdown in the blower control circuit, including the blower switch. The blower fuse is a 40A multi-fuse in slot No. 12 in the engine compartment fuse panel. Check the diagram under the fuse panel lid for the fuse labeled "Blower." Change the fuse and test the system, and if it still fails to operate or blows the fuse again, proceed to check the other components that control the blower.
Blows Only Cold Air
Low coolant level in the radiator causes poor circulation through the heater core, leading to poor heating and even a complete lack of heat from the vents. Check the coolant level, and top off as necessary with a 50 percent solution of water and ethylene-glycol coolant formulated for aluminum radiators, then retest the system. If the heater still doesn't blow hot, then you may have a bad heater control assembly or temperature actuator causing the problem.
Air and Mode Control Failure
If you find that the air intake will not shift between outside and interior air, then you have an issue with your heater control assembly, mode actuator or intake actuator. The control assembly and actuators control the various doors within the air handler that control the intake source, and diverts air from the blower through the heater core then through the floor, console and windshield vents. Shift the vent controls and listen for a slight clunk as the control doors respond to different temperatures and vent selections. If there are no noises and concurrent shifts in vent output, then your problem is likely in this area.
Other components and situations can cause also cause problems. The heater hoses can break down internally and allow the hose to delaminate and release bits of rubber that can act as a check valve to prevent flow. Sedimentation and buildup of detritus caused by corrosion elsewhere in the system can clog up the heater core and prevent circulation. With the engine hot and the heater on full hot, feel the temperature of the heater hoses. If one hose feels decidedly warmer than the other, you have a circulation problem in the core or the hoses.