There are many electrical components inside an air conditioner unit. From relays to contactors to electric motors and wiring it has to work together and working properly for your air conditioner to run smoothly. It is almost like a ballet and the air conditioner sequence of operation follows a specific sequence to work properly For the purpose of brevity the focus of this article will be on the condenser and the electrical components in an air conditioner condenser. From the disconnect box on the wall next to the condenser all the way through the control panel and into the components we’ll cover all the various electrical components and how they work together to make your air conditioner work.
Fuse Box or Disconnect
The fuse box or disconnect for the air conditioner condenser is required by NEC code and should be within reach of the condenser. The fuse box should have a way of protecting the circuit for the condenser. Despite the breaker in the main panel an air conditioner disconnect box needs to be fused or have some sort of trip protection in case of an electrical problem occurs inside the condenser with an electrical component. The protection should be sized according to the ampacity of the air conditioner as rated by the manufacturer. This information is available for unit ampacity and fuse size on the name plate on the side of the condenser. The wire supplying the air conditioner unit should be sized according to NEC tables at 125% of RLA or Run Load Amps which is also rated on the unit plate with other air conditioner nomenclature. The fuse should be sized no larger than 175% of RLA of the unit and with exceptions can be raised to no more than a maximum of 225% of RLA. This allows for the fuses to be able to overcome the start amps of the unit. Start amps are usually referred to as LRA or Locked Rotor Amps which can far exceed the RLA for the first split second when the unit starts. Refer to Article 440.22 of the NEC for more information on this but those are the basics for disconnects, fusing and wiring for the disconnect. On a side note – the fuses used in a fused disconnect should be dual element fuses and often referred to as slow blow fuses. These fuses are designed to handle the inrush current on equipment start-up.
Wiring and Components in the Condenser
Wiring inside the condenser can be classified as control wire and line voltage wire. The control wire in residential air conditioner systems originates at the thermostat and is 24 volts. This controls all the relays and contactor in the air conditioner and runs through any safety or limits in the condenser. What type of safeties can be in the condenser? Refrigeration pressure switches are commonly used in the higher rated equipment. Some manufacturers put high pressure refrigeration switches in all their condensing units. In higher end condensers you will also find low pressure refrigeration switches. These switches will trip the system shutting it down because extreme high pressure and low pressure in the condenser can cause serious issues and it is better to shut the system down as it needs repair to correct the problem. Additionally an air conditioner condenser can have a delay switch in the control circuit to prevent the condenser from short cycling in various cases. Short cycling is bad for the electrical components in the air conditioner condenser especially the compressor which can be irreparably harmed if short cycling occurs.
The line voltage wiring carried the voltage and amps to the fan motor and the compressor. It is very important that all the connection in the line voltage circuit are very tight. Lose connections cause problems with build up of heat and corrosion on the connections. Eventually the heat and the corrosion will cause the wire to break off from the connection altogether and failure of the compressor or fan motor. In the line voltage circuit inside a condenser of a residential air conditioner are a contactor, run capacitors for the compressor and condenser fan motor, and the condenser fan motor and the compressor. If the system requires a start capacitor the start capacitor for the compressor will also be in the circuit for the air conditioner condenser. There will be a potential relay in the circuit that will also be wired to line voltage as the potential relay uses line voltage and not control voltage.
These are the main electrical components in the air conditioner condensing unit. Additional information on air conditioner condensers can be found in the air conditioning category and the refrigeration category.