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What you will learn from this article Air Conditioner Condenser Electrical Components:

  1. Brief description of air conditioner condenser electrical components
  2. Code requirements for the condensing unit feeder circuit, fuse box, and wire running to the condenser
  3. Wiring inside the condenser
  4. Description of various electrical components inside the condenser
  5. Lots of resource and related links to help you learn more.

Air Conditioning and heating equipment uses high voltage. Caution is always advised when working around high voltage. When in doubt call a professional. Safety First!!

Air Conditioner Condenser Electrical Components

Air Conditioner Condenser Electrical Components - There are many electrical components inside an air conditioner unit.air conditioner condenser electrical components From relays to contactors to electric motors and wiring. It all works together to make your air conditioner 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.

Related Link: Read more about condensing units (opens in a new window)

Fuse Box or Disconnect

Air Conditioner Condenser Electrical Components

Air Conditioner Condenser Service and Repair

The disconnect is attached to the wall behind the condenser. Line Set Runs Neatly Up the Side of the House to the Attic.

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 at least have some sort of trip protection in case an electrical problem occurs. An electrical problem 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 nameplate on the side of the condenser. The wire supplying the air conditioner unit should be sized according to NEC tables. The wire should be able to handle 125% of RLA or Run Load Amps which is also rated on the unit plate with other data.

NEC and Electrical Data

Air Conditioner Condenser Electrical Components

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. With some exceptions 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.

Related Link: Read more about the NEC and HVAC including Branch Circuit Conductor Sizing  for air conditioner and heating equipment (opens in a new window)

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(s) 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. This happens because extreme high-pressure or low-pressure in the condenser can cause serious issues. 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.

Resource Link: Learn about control circuits for air conditioning and heating systems (opens in a new window)

Other HVAC Electrical Components

Start Capacitor with Potential Relay condenser

Start Capacitor with Potential Relay - Air Conditioner Condenser Electrical Components

The line voltage wiring carries the voltage and amps to the fan motor and the compressor. It is very important that all the connections 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 will occur. 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.

Resource Link: Learn how start capacitors help motors start when extra torque is needed (opens in a new window)

Air Conditioner Condenser Electrical Components - Crank Case Heaters

Many air conditioners and heat pumps have crankcase heaters to prevent migration of refrigerant to the compressor crankcase in low ambient temperatures outside. The crankcase heater is designed to protect the compressor from liquid refrigerant on start up. Liquid does not compress therefore liquid can and will damage mechanical components inside the compressor. The crankcase heaters keeps the oil in the crankcase hot to prevent the liquid refrigerant from damaging the compressor through liquid slugging.

Some crankcase heaters are controlled with a temperature switch so when the temperature outside drops the crankcase heater is switched on while other crankcase heaters remain on all the time with no switching at all except the breaker or disconnect for the condenser.

In the event of a power loss, many manufacturers recommend letting the air conditioner sit for 24 hours after power is restored. This is to allow the crankcase heater to dissipate any liquid in the compressor that may be in the compressor as a result of vapor condensing when the power loss occurred.


Finally, in conclusion, 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.

High Performance HVAC

Air Conditioner Condenser Electrical Components


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Technical Resource: Refrigeration and Air Conditioning Technology

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