Almost every single electrical system on a car is powered through some kind of switch or electrical relay, and the AC system and compressor are no exception. The AC compressor relay is responsible for supplying power to the AC compressor and clutch. Without this relay, the AC compressor will not have power and the AC system will not function.
The AC compressor relay is no different then other electrical relays - its electrical contacts will eventually wear or burn out, and the relay must be replaced. When the AC compressor relay has failed or is beginning to fail, it will begin to display symptoms that indicate it may be time for it to be replaced.
1. Inconsistent cooling
The AC compressor is powered by the relay. If it is not functioning properly, then the AC system will not be able to produce cold air correctly. When a relay is starting to fail, it may give weakened or intermittent power to the compressor, which will result in weakened or intermittent function of the AC. The AC may function fine in one instance, and then shut off, or deliver inconsistent performance in another. This may be a potential sign that the relay may be going out.
2. AC compressor is not turning on
One of the most obvious signs that the AC relay may have a problem is that the compressor is not coming on at all. In most cases, when the AC is turned on you will be able to hear the compressor switch on. It will usually produce a familiar clicking noise from the clutch being activated. If when you turn it on you do not hear the clutch being turned on, then perhaps it may not be getting power, due to a failed relay.
3. No cold air
Another symptom that the AC relay has potentially failed is that there will be no cold air at all from the AC. If the relay fails, the compressor will not operate and the AC system will be unable to produce any cold air at all. While there are several reasons as to why an AC may stop producing cold air, a failed relay can be one of the most common.
If you are experiencing issues with your AC system and suspect that your AC relay has either failed or is beginning to fail, we recommend having it diagnosed by a professional technician. If your AC relay is found to be faulty, they will be able to replace the AC relay if necessary.
This article originally appeared on YourMechanic.com as Signs of a Bad or Failing AC Compressor Relay and was authored by Eduardo Ruelas.