2011 Hyundai Accent AC compressor doesn't kick in

Question

I own a 2011 Hyundai which is known as Accent model in the US. The problem is my AC doesn't work, namely the AC compressor clutch doesn't engage when turned on. What happens is when the AC button is pressed the LED indicator light comes on, and I clearly can hear a relay under the hood clicking. I've measured the voltage on the compressor single-wire electrical connector and it's effectively zero whether the AC is on or off. I also checked if there is any pressure in the system and both H and L valves gave me a distinctive sound on pressing.

I suspect the ECU might cut off the power on the wire due to low refrigerant pressure but why would the relay click then? Wouldn't one expect the signal to be cut off before the relay as it's much weaker than after? Things are complicated by the fact that the wiring has apparently been redone by one of the previous owners. So my question is should I dig into AC wiring or just get the system recharged?

UPD 1: checked the wiring diagram and, indeed, the ECU controls the relay, not the compressor wire. So either there are 2 quick clicks (on/off) which I perceive as one or the wire is damaged. Think I'll proceed with checking the voltage on relay winding connector (the ECU control signal) and the compressor wire integrity.

UPD 2: the system didn't have enough refrigerant, so after a proper charge it works ok now.

Answer 1

First I would confirm you have proper charge. You will need gages for this. Just listening for a hiss is insufficient. Then I would check the primary circuit to the relay as you decided to do. Then you can jump your secondary circuit at the relay to see if the pump activates. Caution should be taken when checking primary circuit when it is computer controlled. Since it sounds like you don't have equipment for this you might consider having it dissed out by a reputable AC shop.