If it is the relay, then this is typically situated on the compressor. There are different arrangements of relay. It sounds like you have one with a round cut-out. If this is operating every few seconds or so, it can be due to a faulty relay or a faulty compressor. If the relay is a gravity device it is possible to give rough and ready check with a multi-meter. If the relay is fine then check the Compressor windings for short-circuits. If possible read the current flowing in the windings and ask for further details
Chris_Y, December 2004