Air Conditioner (A/C) Relay

March 28, 2017

The air conditioner (A/C) relay, is a relay used to send electrical power to the air conditioning compressor, and air conditioning compressor clutch when the system is turned on. It operates just like any other relay, and is often controlled by a button labeled ‘A/C’.

Symptoms of Wear or Failure of the A/C Relay

  • Air conditioning compressor works intermittently (randomly): as the relay wears out, many times they will turn on the A/C compressor at random intervals. This is because the electrical contacts inside the relay may not be totally worn, but they do not have a good connection.

  • Vents blow only warm air: while this could be a few other issues, and most commonly is, the A/C relay may have failed, preventing the A/C compressor from receiving the signal to start. This will be accompanied by the absence of the normal ‘click’ sound heard when turning on the A/C.

  • A blinking A/C light will alert you to an air conditioning issue, but not normally if the relay has failed.

Related Repair Advice

  • While simply replacing the relay seems cheap, fast, and easy, the result is normally just as cheap. If you suspect the relay has failed, it should be tested prior to replacement.

  • If the relay clicks when the A/C is turned on, this does not mean that power is flowing through the relay, it only means the relay is receiving electrical power. This is another reason testing is important, as the relay could seem good, but not route power to the A/C compressor.

  • There are other switches that control the A/C system, and a few of them will prevent the A/C from running by interrupting the signal to the A/C compressor. This is yet another reason why diagnosing the issue properly before buying parts is essential.

  • Many vehicles that use A/C compressor control valves always have the compressor running, and some will not use an A/C relay. Instead, the amount of work the compressor can do is limited by the compressor control valve, and moderated by the engine control module.

About the Author

RepairPal is the leading online source of auto repair resources and estimates. With many ASE Master certified mechanics on staff who have decades of experience, RepairPal knows all the fine points of car repair.

No comments yet…

Sign in to comment

Related Questions

See what others have asked about this, or visit the Questions page to ask your own question.
Does the ac have a relay switch, if so is it a suzuki part or can it be purchased elsewhere?
The ac on my truck will work sometimes and then other times it blows out hot air. is this a result of low freon,...