Cooling Fan ON Conditions

205

TM 9-2320-312-24-2

Troubleshooting Section

Engine start-up

The coolant temperature is less than 92 C

(198 F).

The "A/C Pressure Switch Fan On Time" is

The fan has been ON for at least 30 seconds.

programmed to less than 30 seconds.

The inlet manifold air temperature is less than

During engine start-up, the ECM will keep the fan

ON for two seconds after the engine has reached

53 C (127 F).

the programmed low idle (700 to 800 rpm). The fan

The strategy for the exhaust brake is not active

will be ON continuously if the electrical circuit to the

cooling fan air solenoid valve has an open circuit or

and the "Fan with Exhaust Brake ON" parameter

if the ECM Fan Relay circuit is opened.

is programmed to "YES".

The A/C high pressure switch is not active.

Cooling Fan ON Conditions

The PTO on/off switch is in the OFF position and

The ECM will turn the cooling fan ON under any of

the following circumstances if engine speed is less

the "PTO Activates Cooling Fan" parameter is

than 2750 rpm:

programmed to "Continious".

The engine is not running.

The manual fan override switch is OFF.

Engine cranking

A/C High Pressure Switch Input Connected to

A/C Control Unit.

The coolant temperature is greater than 96 C

A control unit for the A/C that is supplied by the

(205 F).

OEM may be used. The control unit for the A/C

Active diagnostic code for the coolant temperature

determines when the cooling fan should operate.

This is based on the following input information:

sensor

The inlet manifold air temperature is greater than

A/C high pressure switch

87 C (189 F).

low pressure switch

The inlet manifold air temperature is greater than

evaporator thermostat

72 C (162 F) while the boost pressure is greater

than 70 kPa (10 psi).

The output for the fan for the control unit to the

The manual fan override switch is on.

A/C is designed to interface with the ECM. The

output for the fan may be connected to the input

The "Fan with Exhaust Brake ON" is programmed

for the A/C high pressure switch. The input for the

A/C high pressure switch is Input 11 of the ECM

to "YES" and the exhaust brake has been on at

connector J1/P1 terminal 41. The fan is in the ON

least two seconds.

position when the A/C high pressure switch is in

The "A/C Switch Fan On-Time" is programmed

the OPEN position. This type of control has a time

delay. Typically, the "A/C Switch Fan On-Time" is

to a value above 0 and the A/C high pressure

programmed to one second since the control unit

switch is open.

for the A/C provides an additional time delay.

The ECM is counting after the A/C high pressure

switch has closed.

The Cooling Fan Control can be Operated

Independently of the ECM.

The "PTO Activates Cooling Fan" parameter is

Operation of the cooling fan control can be

programmed to "Continuous" and the PTO on/off

controlled independently of the ECM. The OEM

switch is on.

installed air conditioning high pressure switch may

be used for independent cooling fan control. A cab

The last four items in the previous list are dependent

mounted override switch in the solenoid circuit can

upon the programming of the Customer Parameters.

also operate the cooling fan.

Note: The ECM will turn OFF the cooling fan for 10

seconds during engine shutdown.

Troubleshooting

Before troubleshooting the cooling fan circuit,

Cooling Fan OFF Conditions

determine the type of fan drive system that is used.

The fan drive can use the following controls in order

The cooling fan will be turned OFF by the ECM

to control the fan:

if engine rpm exceeds 2800 rpm or when all the

following circumstances are met: