TM 9-4120-378-14
Section IV. UNIT TROUBLESHOOTING
4.12 GENERAL.
4.12.1 This section provides information useful in diagnosing and correcting unsatisfactory operation or failure of the
air conditioner. Each malfunction is followed by a list of probable causes and actions to take to remedy the malfunction.
You should perform the tests/inspections and corrective actions in the order listed.
4.12.2 This manual cannot list all malfunctions that may occur nor all tests or inspections and corrective actions. If a
malfunction is not listed or is not corrected by listed corrective actions, notify your supervisor.
4.12.3 Control Circuit. The cause of a system's failure to operate can be greatly narrowed if control that caused the
failure can be isolated. It is the function of safety devices to open the circuit under certain conditions; therefore,
additional checking may be required to determine whether the safety device is open because it is bad or because it is doing
what it is supposed to do. The following steps contain instructions for checking the control circuit.
a. Disconnect power from the air conditioner.
b. Test continuity across each control in the affected circuit, using an ohmmeter. Refer to the appropriate schematic
diagram and wiring diagram (Appendix F) as a guide to the connections in the circuit.
c. Replace defective parts.
4.12.4 Safety Devices. When testing the control circuit and other equipment you must take into consideration the fact
that open safety devices may not be bad. It maybe normal for the device to be open under the existing conditions, or it
may indicate trouble elsewhere in the air conditioner.
Refrigerant under pressure is used in the operation of this equipment.
HIGH VOLTAGE is used in the operation of this equipment. DEATH ON CON-
TACT may result if personnel fail to observe safety precautions. Never work on
electrical equipment unless there is another person nearby who is familiar with the
operation and hazards of the equipment and who is competent in administering first
aid. When the technician is aided by operators, he must warn them about dangerous
areas.
Whenever possible, the input power supply to the equipment must be shut off before
beginning work in the equipment.
