TM 9-2320-366-34-1
1-14. ELECTRICAL SYSTEM (CONT)
Figure 1-21. Material Handling Crane (MHC) System
h. Material Handling Crane (MHC). The primary electrical components of the MHC System are the REMOTE
CONTROL UNIT (1, Figure 1-21), junction box (2), overload shutdown box (3), tension load cell (4), left and right side
jack cylinder proximity sensors (5) and several function and lockout solenoids. When the operator selects an MHC
function using the REMOTE CONTROL UNIT, electrical current is sent through the junction box and to the appropriate
solenoid. When energized from the REMOTE CONTROL UNIT, the function solenoid controls hydraulic pressure to
the function selected by the operator. When the function solenoid is de-energized, hydraulic pressure is removed and
the function stops.
The overload shutdown system controls the lockout solenoids. The lockout solenoids prevent
operation of certain MHC functions when an overload condition is sensed. Overload conditions are sensed, in
combination, by the tension load cell and a microprocessor inside the overload shutdown box which monitors boom
angle and extension. When an overload condition is sensed, the boom up/boom down, hoist up, telescope out functions
are locked out. The hoist down and telescope in functions will still operate and allow the operator to safely lower the
load to the ground. When the power switch on the remote control box is used as an emergency shutdown, all MHC
functions are locked out. The left and right side jack cylinder proximity sensors prevent operation of the MHC until both
jack cylinder outrigger pads are lowered fully to the ground.
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