Pre-Test Preparations

Determine whether there is a system malfunction or if the system was improperly operated. It is possible for the system to go into a maximum heat or cooling mode which will rapidly change the passenger compartment comfort level if the operator changes the selected temperature setting by four or more digits.
Check for proper coolant level, water valve operation, refrigerant charge, drive belt tension, engine vacuum connections, radiator air flow, radiator fan operation and the in-vehicle sensor air intake suction.
Allow engine to reach normal operating temperature, then perform test procedures, then after all test procedures are completed, ensure proper operation of system.