Thermo King 920000, Manual

Page: 61 / 190

Electrical Maintenance
61
Zone 1 Evaporator Defrost Cycle
Diesel Operation
The Defrost cycle can be initiated with the
M
ANUAL
D
EFROST
key, by the air switch, or by the defrost
timer in the TG-V Controller when the defrost
termination switch is closed.
Initiating the Defrost cycle energizes the defrost
relay, which energizes the HGS circuit and the 29
circuit, and opens the LLS-FER circuit. The HGS
circuit energizes the HGS, LLS, and CIS (and the
RTPS and PV when the RTPC is closed). The 29
circuit causes the TG-V to energize the 2K relay,
which shifts the condensing unit into high speed.
Opening the LLS-FER circuit de-energizes the
evaporator fans.
The CIS and HGS divert heated refrigerant vapor
to the evaporator coil, melting frost.
De-energizing the evaporator fans keeps the heat
in the evaporator and prevents warm air from
passing over the load.
NOTE: The unit will not Defrost during normal
unit operation unless the Defrost cycle is
initiated while the evaporator temperature is
below 42 F (6 C).
The defrost termination switch will open and
de-energize the defrost relay when the frost has
melted and the evaporator temperature rises above
52 F (11 C). The TG-V Controller then determines
the mode of operation.
Zone 1 Evaporator Defrost Cycle
Electric Operation
The Defrost cycle on electric standby operation is
similar to the Defrost cycle on diesel operation.
Zone 1 Evaporator Defrost Cycle
Checkout Procedure
To check the Defrost cycle, run the Zone 1
evaporator on Cool until the evaporator coil
temperature is below 42 F (6 C). Push the
M
ANUAL
D
EFROST
key.
If the Zone 1 evaporator shifts to Defrost
momentarily but shifts out of Defrost when the
switch is released, check the TG-V Controller. See
“Field Test Procedure for Multi-Temperature
In-Cab TG-V Controllers” on page 72.
If the Zone 1 evaporator will not shift to Defrost,
or if the Defrost cycle will not terminate, see the
following Defrost checkout procedures.
CAUTION: This unit is equipped with
Auto Start. It will start automatically if the
O
N
key is pressed while the On/Off
switches are in the On position.
CAUTION: CYCLE-SENTRY Equipped
Units—Place the Auto Start/Stop -
Continuous Run switch in the Cont Run
position before performing any diagnosis
and service operations on the unit. The
unit may start at any time without prior
warning if the
O
N
key has been pressed
while the On/Off switches are in the On
position and the Auto Start/Stop -
Continuous Run switch is in the
CYCLE-SENTRY position.
CAUTION: Do not forget to remove the
jumper wires from the unit after checking
or testing unit components.