What are three common methods of head pressure control during low ambient?

low pressure switch will detect low evaporator pressure and shut the comp down.

or the over load will stop the compressor if the thermostat didn't ,

Pressure head can be controlled pressure switch. When low ambient and no need for cooling then the chilled water consumption is low or ref consumption will low and the pressure will be increased inside the pipes because of not being used by chilled water system or compressor of DX System in VRVs.

The high pressure in pipes indicate the system to be reduced either by VSD or totally shutoff.