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Detailed Introduction on Fan Motor

By Susi | Published on Dec 10,2015

Working Principle

Working Principle of electrical fan is magnetic dynamics. The main part of fan is AC motor.

Energized coil force to rotate in a magnetic field. The form of energy conversion: the electrical energy is mainly transferred into mechanical energy, and because the coil has a resistance, so that there is an inevitable part of the electrical energy converted into internal energy. Energized to produce a rotating magnetic field to drive the rotor to rotate.

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Fan motors are the unsung “heart” of HVAC equipment. They work unobtrusively and quietly for years, often under tough conditions. They don’t need a lot of love, but they do need periodic attention and it’s up to you to provide it. The cost of overlooking regular testing and maintenance of motors can be an HVAC system that grinds to a halt, so be sure to check the motor on every maintenance and service call.

Check the Power and Windings

When you arrive on a jobsite in which a unit’s fan motor is not working or the high-limit switch has tripped, the first thing to check is power to the motor and/or unit. If there is proper voltage, check the low-voltage control circuit. Check for proper voltage at the transformer and check for a fuse in the low-voltage circuit. Make sure the circuit breaker is not tripped (or the fuse is not blown). If the circuit breaker is tripped (or fuse is blown) or if the transformer is bad, it could indicate a short in the motor. In that case, check the windings in the motor before turning the power back on.


The main causes for the ac fan motor not working basically are: winding circuit, lack of oil holding shaft, abnormal capacitance, etc. From the maintenance of fan motor, the last two kinds of fault is much more common. The maintenance steps are: test plugs, motors, capacitor, and then processing.

The first step, measure the running condition of electric fan and control winding. First rotate the electric fan timer. When hearing a clicking sound, it means the timer is normal. If not, it means the timer get broken. If the timer is normal, set the multimeter to R x 100 Ω files, using one hand holding two multimeter to clamp fan power plug, another hand to push electric fan gear switch and measure the operation of the fan motor and speed regulating winding resistance. Most of the electric fan normal resistance value is between 600-1000 Ω. The difference of resistance value in each gear is 100. If resistance value is consistent, the electric fan running speed winding is normal. But, it can't say fan motor is at work because motor, start winding, as well as winding have the possibility of a partial short-circuit. If there is no resistance, the possible reasons are: a motor winding burned and caused circuit break; thermal fuse get open circuit (disassemble the motor and have a look, and if it just open circuit, joint thermal fuse and can get it back to normal; all gear switch are broken, but it not likely happens.


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A broken fan motor can make your air conditioner useless and your ride miserable. Luckily, a broken 12-volt fan motor can be replaced at home. Here's how to take out the old fan and put in a new one, complete with step-by-step photos.

It's hot. Really hot. A wave of shimmering, sauna-hot air hits your face and takes your breath away as you open the door and settle into the car. Too bad there wasn't a tree anywhere near this steamy, black asphalt parking lot. Who would think a car's interior could get this hot?

You immediately thumb the a/c controls and wait patiently for relief. A brief moment of warm air from those vents turns the sweat beading on your forehead into crunchy little salt tattoos. Within seconds, the air begins to cool off, and so do you. Not a moment too soon.


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