Central air-conditioning units are complex, and they require periodic maintenance in order to keep them operating properly. With the combination of refrigerant under pressure, electricity that powers and controls the movement and compression of these refrigerants, and the various controls that are required in order to make everything work as it is supposed to, a small problem with a central air-conditioning system can become a confusing and complex repair. One of the most common questions asked is where the transformer is located on the central air-conditioning system.
Inside transformer and fan control transformer
There are a number of different transformers in a central air-conditioning unit, and the main one is not located on the air-conditioning unit at all. The transformer, located inside of the house on the furnace or fan coil unit for the air-conditioning, is a small black or brown electrical component that is normally located on the inside of the furnace or mounted just outside the furnace. The transformer changes the voltage of the electrical control signals that are transmitted by the furnace's 12-volt circuit board, into 120-volt signals that are transmitted to the air-conditioning unit. This allows the air-conditioner and the fan to communicate at the same time to turn the fan on and off or to cycle the air-conditioning unit.
Transformers on control board of the air conditioning unit
There may also be a transformer mounted outside on the air-conditioning unit. This transformer is usually located near the control wiring for the outdoor condenser coil that is mounted underneath a protective cover plate on the outside of the unit.
Transformers on control board of the furnace
Other transformers may be located on the control board of the furnace or fan coil that are smaller and are soldered into integral parts of the control board. These transformers serve to amplify or decrease voltage from 120-volt alternating current to 12-volt direct current to power different parts of the furnace system such as the inducer motor or the fan motor.
Transformers on compressor
There may also be a transformer located near the compressor wiring or near the capacitor for the outdoor condenser unit. These are typically inside of the center of the coil on the outdoor unit and you may need to remove the cooling fan to access them.