A method of maintaining a fluid flow rate in a heating, ventilating, air conditioning, and refrigeration (HVAC-R) system while maintaining superheat in the HVAC-R system at a desired level includes: continuously measuring an operating fluid temperature of the HVAC-R system and calculating superheat at a pre-determined rate, determining if the calculated superheat is stable, measuring and recording an operating fluid pressure of the system each time the calculated superheat is stable, recording an average operating fluid pressure each subsequent time the superheat is stable, calculating an output PWM and reducing fluid flow through a metering valve when an actual PWM is greater than the calculated output PWM by adjusting a PWM signal to a microvalve in the metering valve, and increasing fluid flow through the metering valve when the actual PWM is less than the calculated output PWM by adjusting the PWM signal to the microvalve.