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 TM 55-1905-223-24-17
2
A to C-Same as step 1.
3
B to C = Same as step 1.
(3) Always check voltmeter readings against supply voltage ratings on HVAC equipment electrical
nameplates. If a low voltage exists at an HVAC unit, check the voltage again at the electrical
supply entrance to the distribution panel to be sure a "voltage drop" does not exist in the branch or
feeder circuit leading to the unit.
(4) Applying or operating a unit or specific component continuously at either voltage extreme (+10% or
-10%) is poor practice and a shorter component life is to be expected.
b. Overload Devices.
(1) Fuses.
WARNING
Turn electrical power OFF at primary breaker to fuse block.
(a) Check for defective fuses as follows:
1
Secure all power to the fuse block.
2
Remove fuses from the circuit.
3
Check the "continuity" of each fuse with an ohmmeter. Apply an ohmmeter lead to each end of
the fuse.
4
An "OPEN," or infinite, reading indicates a defective fuse that must be replaced.
5
A "CLOSED," or ZERO, reading usually indicates that the fuse is good. Install the fuses back
in the circuit.
(b) If a fuse has indicated a "CLOSED" condition, but is still suspected as being defective, do the
following:
WARNING
Turn electrical power OFF to avoid personal injury.
1
Secure all power to the fuseblock.
2
Remove the wires from the load side of the fuses.
2-35
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