Condenser Fan Motor
The condensing unit fanis responsible for pulling air through coils of the condensing unit. They pull air through the condensing unit coils. It runs the gamut in horsepower ratings from low fractional horsepower in small residential units all the way up to 1 horsepower (and larger) 3 phase motors in large commercial HVAC units. It is usually direct drive to a propeller blade which creates the air flow. Its job it to move air. A specific quantity of air through the condensing unit coils so that a heat exchange process can take place and rig the condensing unit of the heat it absorbed indoors or in the case of the heat pump in heating mode to absorb heat from the outside air and send it inside. It is the process of refrigeration and all the components work together to achieve one result and that is to move heat from one place to another.
In straight air conditioners the air conditioner fan is used mainly in the summer or when the air conditioner is running. During the winter this fan sits idle until the air conditioner is turned back on in the spring when temperatures begin to rise.This can be a problem for the air conditioner motor. Sitting all winter without any motion the bearings and shaft in the air conditioner motor can seize up or rust. It is important that the air conditioner motor be checked to ensure it is running especially when it is first turned on after sitting idle all winter. This is a good reason to have air conditioning spring maintenance performed by a professional.
The heat pump motor, on the other hand, sees run time during the winter because the heat pump motor needs to run to produce heat. The heat pump motor, like the air conditioner motor, is direct drive to a propeller blade which pulls the air through the condensing unit coils. Sometimes, people will hear the heat pump unit running but the fan will not be turning. This is usually when the heat pumps kicks into defrost mode in the winter and should only be a temporary occurrence that only happens when the heat pump unit is in defrost mode.
Condensing Unit Fan Problems & Troubleshooting
Sometimes problems can develop with the condensing unit fan that needs the attention of an HVAC professional or sometimes a handy DIYer. Since the condensing unit fan is an electric motor and out in the open and subject to the weather and changing weather conditions including temperature extremes the condensing unit fan must be rugged and durable enough to handle these extremes including rain which can kill any motor quickly if water gets inside it. Many HVAC manufacturers take great pains to protect the fan from the elements including keeping the fan from getting wet. Here are a few common problems that happen with fans which generally need the attention of a professional HVAC technician simply because the condensing unit is really a dangerous place to work around as the condensing unit can start automatically and severe injury can result so there is a danger unless one is trained at working safely around the condensing unit.
The condensing unit fan blade sticks and will not turn when the unit kicks on. Usually this is a result of moisture and rust which will prevent the motor from turning even though is has power on it. Sometimes a quick flip with a screw driver (being very careful when doing it) will get it started again.
Another cause of a frozen blade can be the result of a bad or weak capacitor as the motor needs the torque boost a capacitor provides to the single phase motor.
Another problem with the motor can be a bad contactor or relay and a bad contactor will also effect the compressor. If it is a bad relay it is likely a heat pump and not an air conditioner as most heat pumps control the motor through the heat pump defrost control board. In the case of the heat pump the relay is located on the defrost control board and looks like a black cube. The entire board needs to be replaced as the black cube is integral to the board.
Some additional notes on condensing unit motors. If the motor is replaced then it is always prudent to replace the run capacitor at the same time first to ensure the run capacitor is properly rated for the new motor and secondly to make sure the capacitor will last as long as the motor (at least ideally). Additionally, a closed case motor is preferred to prevent water from getting inside the motor where the windings and other electrical components are located. On condensing unit fan replacements there is usually a plug on the bottom or top of the motor. The part of the motor facing down should have the plug removed to allow water to drain out of the motor in case water gets into it. Additionally it is important to make sure the fan blade rotation is correct. The air should be blowing up from the unit as the fan blade pulls air through the coil and discharges it out the top. Many aftermarket motors have a wiring diagram on the motor for reversing rotation so that air is being pulled through the motor.
Condenser Fan Motor - Conclusion
If you have a failed motor it will cause severe issues with the refrigeration system especially when the temperatures and the load is high. The compressor will trip either on a high pressure switch or on its own internal overloads because of excessive pressure and heat. This excessive heat can be hard on a compressor and the internal components of the compressor so a healthy condensing unit fan is important for the proper operation of the refrigeration system and the durability of the compressor. Make sure the condensing unit fan is maintained properly and you will likely avoid several problems with the other major components of air conditioner or heat pump condenser system.