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T
HEORY
HSM-24/5S (208-240V, 230V)
Electrical power is supplied into the unit to the main terminal block, the
contactor and the ON/OFF switch. When the ON/OFF switch is selected to the ON
position, line voltage is supplied to the A1 and A2 terminals of the contactor. The
contactor activates and supplies power to L1 and L2/N terminal blocks, the fans,
and the 12 VDC power supply.
12 VDC is supplied to fuses FB1 and FB2 from the power supply. The DC+ and DC-
terminal blocks are the connection points for the lights.
Line voltage is supplied to the L1, L2/N, and COM terminals of the temperature
controller from the L1 and L2/N terminal blocks. The RTD temperature sensor
provides a resistance signal into the temperature controller corresponding to
surface temperature of the shelf it is mounted to. The temperature controller
monitors the requested temperature from the temperature control knob setting
and the shelf temperature from the RTD temperature sensor. When a call for
heat is made, the temperature controller closes the NO contacts of the relay. L1
voltage is supplied to the terminal block and then to one of the black wires of the
heating pad. The other black wire from the heating pad is connected to the L2/N
terminal block. The white wire from the heating pad is connected to the terminal
block with no other connection. The two coils in the heating pad are connected in
series. The indicator light illuminates signaling the call for heat from the
temperature controller.
When the shelf has reached the requested temperature, the temperature
controller opens the NO contacts of the relay. L1 voltage is no longer supplied to
the heating pad. The indicator light goes out.
H ea t e d S h el f M er c h a n di s e r
S e r v ice Man u a l
MN-390 54
R ev 1
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