Thermo King MD-MT - CYCLE-SENTRY Diagnosis; Relay and Control Module (CSM) Fault Diagnosis

141
CYCLE-SENTRY Diagnosis
Condition Possible Cause Test Procedure
Run relay will not energize when
required
Open 7A circuit from selector switch
to run relay
Test 7A circuit
Defective selector switch Test circuit from 7M or 7MA to 7A on
switch in the CYCLE position
Open 7M or 7MA circuits Test 7M and 7MA circuits
Open diode from 77, R7C, 7C or 7X
to 7V at multi-temp relay board
Test diode D3, D7, D8, and D9
Defective start run relay Test or replace start run relay
Defective CSM Replace CSM
Defective speed relay (2K or R2K)
not supplying power to the 7X or 77
circuit when thermostat calls for
high speed
Check speed relay (2K or R2K) with
thermostat in high speed mode
Open or high resistance in the
chassis ground circuit to the option
board
Check the chassis ground circuit
from the option board to the battery
Defective run relay Test or replace run relay
Unit will not automatically
preheat but preheats manually
Defective CSM Test or replace CSM
Unit will not automatically
preheat, but run relay does
energize
Defective preheat relay Test or replace preheat relay
Defective CSM Test or replace CSM
Open H circuit from preheat relay to
glow plugs
Test H circuit
Open 2A circuit from alternator to
preheat relay
Test 2A circuit
Fuel solenoid energizes on
continuous operation but will not
energize on CYCLE-SENTRY
operation
Defective run relay Test or replace run relay
Open 8D circuit from run relay to
fuel solenoid
Test 8D circuit
Unit will not automatically crank
but cranks manually
Defective CSM Test or replace the CSM
Unit will not automatically crank
but preheats automatically
Defective start relay Test or replace start relay
Defective CSM Test or replace the CSM
Open 2A circuit to start relay Test 2A circuit
Open 8S circuit from start relay to
starter
Test 8S circuit
Unit cranks prematurely before
proper preheat has occurred
Defective engine temperature
thermistor
Test engine temperature thermistor
Shorted BL1 and BL2 wires from
option board to engine temperature
thermistor
Check BL1 and BL2 wires
J1 in position B Place J1 in position A
Defective CSM Test or replace CSM