The electric heater fan is responsible for pushing hot air out of the unit, which causes the back draft to pull new air in. The air is circulated this way to keep the unit from overheating and help it maintain the proper core temperature. When the fan stops working, the air will simply sit and become stagnant, causing it to eventually overheat and burn out. You can order replacement parts on some heater units directly from the manufacturer. There are several main things that could be causing your fan to not operate properly, which includes, but is not limited to, bad wiring or connections, a failed temperature gauge, or a dead fan motor.
Step 1 - Open the Case and Test Circuits
The first thing to do is use your hex driver or screwdriver to open the case so you can see the electric heater fan. Use your voltage regulator to carefully check the connections, starting at the circuit board and moving to the fan and thermostat. Find and single out the problem area, where the lines are not getting the proper voltages. Your readings on one end of the circuit should be the same on the opposite end of the same circuit unless it runs through a resister. A resister can change the voltages between two connections to prevent overcharging specific components in the device.
Step 2 - Replace the Temperature Guage if Needed
Some units use a temperature controlled electric heater fan. This means that the fan doesn't turn on unless the temperature hits a certain degree of heat output. You can test the fan itself by connecting it to a live power source, and you can do this with several wires connected to the power source. If your fan normally doesn't come on until after the heater gets hot, then it could very well be the temperature gauge. You can also test these connections with your voltage regulator to check for functionality. If the unit does turn the fan on due to the temperature gauge, and it is a failed circuit, simply use a soldering gun to replace the part.
Step 3 - Replace the Fan
If you test the electric heater fan and it does not read as a completed circuit, it is likely that the motor is burnt out. Simply remove the fan from the housing with your hand tools and use the soldering gun to disconnect it from the board. Reverse this process to put your new fan into place and mount it back into the housing. Be sure it is secured properly to avoid the fan from pulling random wires into the blades. Be sure to check any resistors with your voltage regulator as well. If these have been internally burnt out, the unit still will not work after the fan has been replaced.
Step 4 - Close Up the Case
Once the temperature gauge and the electric heater fan have been checked and replaced, if needed, close your case back up. Be sure to place wires and parts back where they originally were to prevent fire and electrical hazards in the future.