First, shut off the unit and remove the control cover to expose the switch. Then connect a test light with alligator clips to the two wire terminals in the low-pressure control. Now, connect the compound gauge to the suction-line service valve and restart the unit as the unit must be running when performing this check. Watch the test light and compound gauge while closing the liquid-line service valve and let the system pump down. Watch for the low switch opening, then open the liquid-line valve and watch for the high switch closing. (It must close as soon as the compound gauge rises to the cut-in pressure.)

CAUTION: Perform these checks for a brief time only to avoid damage to the unit.

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