Thermo King MD-MT, Operator'S Manual

Page: 77 / 192

Electrical Maintenance
77
Door Sentry II
Door Sentry II is a factory option that is designed
to improve temperature control when the doors
are opened during delivery.
The system uses six relays and two door switches.
Four of the relays (XK1, XK2, XK3, and XK4)
are located on a relay module and are controlled
by the Zone 1 (condensing) door switch. The
other two relays (XK5 and XK6) are controlled by
the Zone 2 (remote) door switch. The relay
module and relays are mounted on the terminal
board plate on the inside of the control box cover.
Opening Zone 1 Door
Opening the Zone 1 door closes its door switch
and grounds the coils of relays XK1, XK2, XK3,
and XK4 to energize them. The following occurs:
1. Relay XK1 de-energizes the throttle solenoid.
The condensing unit goes to low speed.
2. Relay XK2 disables the Zone 1 liquid line and
hot gas solenoids.
3. Relay XK4 energizes the Zone 2 liquid line
solenoid and heating or cooling circuits to
allow heating or cooling to continue as
required by the Zone 2 thermostat demand.
4. During CYCLE-SENTRY Auto Start/Stop
operation Zone 1 will operate in a Null mode
but the condensing unit will continue running
until Zone 2 thermostat demand is satisfied.
When the Zone 2 unit thermostat is satisfied,
the condensing unit may shut down.
Opening Zone 2 Door
Opening the Zone 2 door closes its door switch
and grounds the control coils of relays XK5 and
XK6 to energize them. The following occurs:
1. Relay XK5 opens the power circuit to the
Zone 2 thermostat. Zone 2 heating or cooling
stops. The power circuit to the Zone 1 Door
Sentry module is also opened disabling the
Zone 1 Door Sentry Door Sentry functions.
2. Relay XK6 opens the power circuit coming
off the Zone 2 On/Off switch. The Zone 2 fans
stop.
Opening Both Zone 1 and Zone 2 Doors
Because power to operate the coils of relays XK1,
XK2 XK3 and XK4 is removed when the Zone 2
door opens, Zone 1 unit heating or cooling will
not be interrupted when both doors are opened at
the same time.
Functions of Door Sentry Relays XK1
through XK6
XK1 de-energizes the throttle solenoid.
XK2 disables the Zone 1 liquid line and hot gas
solenoids.
XK4 energizes the Zone 2 liquid line solenoid and
heating or cooling circuits to allow heating or
cooling to continue as required by the Zone 2
thermostat demand.
XK5 de-energizes the Zone 2 thermostat and
disables Zone 1 Door Sentry functions.
XK6 opens the power circuit at the Zone 2 On/Off
switch. This cuts power to Zone 2 fans.
1. XK1 3. XK3 5. XK5
2. XK2 4. XK4 6. XK6
Figure 31: Door Sentry-II Relay Identification
AGA745
6
5
4
3
2
1