FIELD (UNIT) MAINTENANCE
LARGE CAPACITY FIELD HEATER
FIELD (UNIT) MAINTENANCE INTRODUCTION
The procedures in this section have been arranged in order in which the items appear in the Unit (O)
Maintenance level column on the Maintenance Allocation Chart (MAC) which is provided in WP 0092.
Step by step procedures have been provided for all actions authorized to be performed by the Unit in
General. Preferred repair methods consist of replacing wires, terminals, connectors, etc. , rather than
splicing wires, bending ends to form terminals, and other makeshift procedures, although the latter may
be appropriate for emergency field repairs.
Soldering Connections. Wire connections must
be made mechanically sound before they are soldered.
Solder alone does not provide sufficient strength to prevent breakage. Joining surfaces of connections to
be soldered must be clean and bright. If a separate flux is used, it should be rosin base flux and should
be brushed onto the joint before soldering. If a flux-core solder is used, it should be a rosin core electrical
solder. If uncored solder is used, it should be a lead-tin solder. Wires should always be heated to the
point at which the solder will melt completely and flow into all parts of the joint. Excessive build up of
solder "gobs" on the joint should be avoided or removed.
Insulating Joints. The preferred method of insulating electrical joints is by the use of heat-shrink tubing.
To apply, cut a piece of heat-shrink tubing of suitable diameter to a one-inch length for covering joints at
terminals or connectors, or to a length about 1/2 inch (1.3 cm) longer than the joint to be insulated, and
slide the tubing over the wire before making the joint. After the joint is made, slide the tubing so that it
covers the joint, and shrink in place with moderate heat.
Splicing Wires. To repair broken or cut wires that are otherwise sound, the mating ends can be stripped
and spliced. A commercial butt splice can be crimped onto the ends to join them, or a `Western Union"
wire splice can be made. The latter is made by stripping 1/4-1/2 inch (6.5-12.7 mm) of insulation from the
wire ends, holding the ends parallel and facing opposite directions, then twisting each end around the
other wire at least three turns. Solder and apply insulation as described above.
Crimping Terminals. To install a terminal on the end of a wire, strip 1/4-1/2 inch (6.5 12.7 mm) of
insulation from the end of the wire, apply a one-inch piece of heat-shrinking tubing (if the terminals are of
the uninsulated type) and insert wire end into the shank of the terminal. Crimp the shank, and install heat-
shrink tubing, if necessary.