Service Call: A commercial customer calls to indicate that the air-conditioning unit in a small office building was running but suddenly shut off. The technician introduces himself to the customer and carefully listens to what he has to say. Before being invited inside, the technician puts protective covers over his shoes. The technician then goes to the space thermostat and finds it set at 74°F; the space temperature is 77°F. The fan is not running. The fan switch is moved to ON, but the fan motor does not start. It is decided that the control voltage power supply should be checked first. The power supply is in the roof condensing unit on this particular installation. The technician explains to the customer the reason for leaving the building and proceeds outside. Safety Precaution: The technician places a ladder against the building away from the power line entrance. Electrical test instruments are taken to the roof along with tools to remove the panels. The breakers are checked and seem to be in the correct ON position. The panel is removed where the low-voltage terminal block is mounted. A voltmeter check shows there is line voltage but no control voltage.