A Hyundai Sonata heating system consists of the engine thermostat, heater blower fuse, main panel, heater core, blower motor resister, air regulator doors and the blower motor. The process of elimination should be used to diagnose the system. It is not a difficult diagnosis if done in a logical progression. The most common problem accounting for 80 per cent of heater failures is the heater blower resister. Its purpose is to regulate the blower fan speeds.
- Skill level:
- Moderately Challenging
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Things you need
- Set of socket drivers
- Phillips screwdriver
- Set of sockets
Diagnose the system from a functional standpoint, determining what works and what doesn't. Start the engine and allow it to heat up. Check the temperature on the gauge. If the engine fails to warm up to over 71.1 degrees C, the thermostat is stuck open and the engine is not supplying enough heat. Replace the thermostat.
Turn the fan on and see if it works. Air should be coming out of the vents and you should hear the fan running. If the fan is running but no air is being expelled from the vents, there may be an actuator door problem. Move the vent switch from floor to defroster and all positions in between. If they do not work properly, there is a problem in the control.
Check the fuses in the fuse box by the driver's side kick panel. If all positions work except one, an air door motor is malfunctioning. Open the glove box and remove all the screws around the glove box inside liner using a Phillips screwdriver. Pull the box out so you can see all the air door motors on the HVAC case. Operate the vent switch on the dash while you watch the air door motors operate. If one does not move in any position on the dash, replace the motor.
Check the operation of the blower motor. If it doesn't work, unplug the blower motor resister. This is a component installed in immediate proximity to the blower motor. This is usually the cause for blower failure in this vehicle. It is usually about two inches to the left of the blower motor. You will notice a small rectangular flat board with two or four screws--depending on the year of the vehicle--securing it to the HVAC case.
Pull the electrical plug out of the component. Set the voltmeter to the 20-volt scale and attach the black lead to a good ground. Turn the ignition switch to the run position and probe the terminals on the harness side of the harness for power, using the red lead. If there is no power, check the fuse for the blower motor in the fuse block on the driver's side under the dash and replace it if it is blown. If it is good, the fan control switch on the dash is defective. If there is power at one of the terminals plug it back into the blower motor resister. Pull the plug off the blower motor and probe it for power. If there is power, the blower motor is faulty. If there is no power, the blower motor resister is faulty.