ELECTRICAL PRECAUTIONS

  Electrical failures are a common field maintenance problem due to the wet environment, shock and vibration, and the possibility of improper power from an engine generator set.

  For the safety of operating and maintenance personnel, the electrical system should be grounded to the frame, and the frame in turn grounded by means of a chain or metal link to the ground if a generator  set in is mounted on the vehicle. All components should be grounded from one to the other, such as the generator set to condensing section to evaporator section. Cables to remote sources of power should carry an extra wire for grounding purposes at the supply plug.

  At the time of manufacture, each system should be given a high potential test to insure against electrical flaws in the wiring. All relays and terminals should be protected against the weather, and all wiring should be covered with protective loom to guard against abrasion. All switches should be of the sealed type, recommended by the manufacturer for use in wet environments. Plus type line connectors should be of the waterproof type. Electrical cables connecting split units should have a watertight cable cover, or should be run in conduit. All wiring should be fastened securely to prevent chafing, and should be clearly identified by wire marking and/or following the color code specified by the National Electrical Code.

  Adequately sized extension cords, plugs, and receptacles must be used to avoid excessive voltage drop. Voltage at the compressor terminals must be within 10% of the nameplate rating, even under starting conditions. Many single phase starting problems on small delivery trucks can be traced to the fact that power is supplied to the compressor from household type wiring circuits through long extension cords, neither of which are sized properly for the electrical load. Single phase and type motors which are used for belt driver a compressor during over-the-road operation must be equipped with a relay to break the capacitor circuit, rather than a centrifugal switch. The variable speed operation experienced during truck operation may cause a centrifugal switch to fail because of excessive wear at low operating speeds. All start capacitors must be equipped with bleed resistors to permit the capacitor charge to bleed off rapidly. preventing arcing and overheating of the relay contacts.

  When units are operated from several power sources be sure all plugs and receptacles are wired in the same sequence, so that the compressor rotation will not be reversed.