a hvac system for a vehicle has a condenser , an evaporator , a compressor , a variable accumulator comprising a piston and an actuator , and a control system operatively connected to the actuator . fluid flows in a circuit from the condenser , to the evaporator , to the compressor , and to the condenser . the variable accumulator is arranged between the evaporator and the compressor . the control system operates the actuator to displace the piston to alter at least one characteristic of the hvac system .