The gl-235 is a differential temperature control for solar heating of pools, spas and hot tubs. This model provides differential control with an adjustable, calibrated water temperature high limit. Automatic nocturnal cooling (for pools that overheat in in hot climates) and recirculate freeze protection functions can be enabled/disabled via internal jumpers. Input power can be either 115 or 240 vac. Includes 1-1. 5 inch three way valve.