Thermo King MD-MT, Operator'S Manual

Page: 65 / 192

Electrical Maintenance
65
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 75.
If the Zone 1 evaporator will not shift to Defrost,
or if the Defrost cycle will not terminate, see the
following defrost checkout procedures.
Zone 1 Evaporator Does Not Defrost
1. Check the evaporator temperature:
Make sure the evaporator temperature is
actually below 42 F (6 C) if the unit will not
Defrost. Use a test thermometer to check the
evaporator temperature.
2. Check the operation of the defrost termination
switch:
If the unit fails to Defrost, place a jumper wire
between the 12 circuit and the CH circuit at
the defrost termination switch. Press the
M
ANUAL
D
EFROST
key. If the unit shifts to
Defrost, check for a defective defrost
termination switch. If the unit still fails to
Defrost, move to step 3.
3. Check for an open in the 12 circuit between
the defrost termination switch and the TG-V
controller. If the 12 circuit is not open, move
to step 4.
4. Check for an open in 11 circuit between the
TG-V Controller and the defrost relay. If the
11 circuit is not open, move to step 5.
5. Check the defrost relay:
If the unit fails to Defrost, check the PS circuit
at the defrost relay socket for 12 volts. If the
PS circuit has 12 volts, the defrost relay is
defective and should be replaced. A lack of
voltage indicates an open in the PS circuit.
6. If the defrost relay works and the evaporator
fan stops, but the unit continues to cool; check
the 26 circuit, the 29 circuit, the CIS, the LLS,
and the HGS.
Zone 1 Evaporator Will Not Terminate
Defrost
If the defrost termination switch does not open
and terminate Defrost less than 45 minutes after
Defrost was initiated, the TG-V Controller should
terminate Defrost.
The Multi-Temp TG-V Controller will record
alarm code 14 if the 11 circuit stays grounded and
the defrost termination on time limit is
unsuccessful.
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.