Why they used one pole shunt contactor in ac condending unit?

I would prefer to see how it is wired before guessing but here goes: On a single phase home ac condenser you need to make/ break only one leg of power to cycle the compressor and fan on and off and that is a less expensive alternative for the manufacturer than a 2 pole contactor would be ( so much for the single pole part of the question). As far as the shunt here is where I am guessing: Air Conditioning and refrigeration compressors have heaters in their oil sumps to prevent refrigerant from migrating to the oil and diluting it which would lower the oils lubricating properties. In the old days these heaters were powered 24/7/365. But now these heaters are turned on only in the compressors off cycle ( via the shunt) because when the compressor is operating the oil is warm enough to prevent refrigerant migration and by cycling the heater to be on only when its needed they are gaining electrical efficiency and thus improved SEER.