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.
A chattering or ticking noise: I've talked a lot in the past about the rumble, pop, and bang noises of a loud furnace. The thing is, a noisy air conditioner is also a sign of trouble, specifically with your compressor. Just before this component fails, it starts hard-starting, which means struggling to turn on. When you first turn on your AC, do you hear a chattering or rattling noise If so, the electrical relay switch that starts your compressor may be wearing out. As with all electrical components
A clicking, rumbling, or rattling noise: Similar to the noises above, a clicking sound when the AC starts could mean that the compressor motor mounts have failed and the motor that distributes cool air from within the compressor has come loose and started thrashing around inside the sealed area that houses it.
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.
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.