Thermo King KD-II SR, Manual

Page: 67 / 182

Electrical Maintenance (Rev. 04/03)
53
Wire 7EA supplies control voltage from the unit to the cur-
rent relay at terminal 4. When the current relay is energized,
control voltage passes through the contacts to terminal 2
and wire 7EB to energize the motor start relay. The C3
capacitor, which is connected in parallel with the control
coil of the motor start relay, works with the motor start relay
to act as a smoothing device to reduce chatter in the motor
start contactor.
Motor Start Contactor Control Coil Circuit
7EA energizes the motor start contactor through the start
relay when the current in T2-T2A exceeds 27 amps
A branch of wire 7EA also supplies control voltage to one
side of the motor start relay contacts. When the motor start
relay is energized, control voltage passes through the closed
contacts and wire 7EB to energize the motor start contactor.
The contacts in the motor start contactor close when it is
energized through the motor start relay. T3E and T3F are
energized and the start capacitors provide the phase shift
and boost in power necessary to start the motor under a
load.