SYMPTOM RELATED DIAGNOSTICS

ON/OFF FAN CONTROL VERBAL COMPLAINT (continued)

Test 257

Checking for a short to voltage

5.Turn the ignition key to the ON position.

6.Turn the override switch to the OFF or normal position.

With the coolant temperature below 170°F (77°C) if the fan turns freely, proceed to Test 1024. If the fan does not turn freely, visually inspect the J1B connector for dirt, corrosion, and evidence of an open. If there is no evidence of an open, replace the V-MAC II module. Retest to be sure the problem has been corrected.

Figure 331 — Voltage from Pin Y2 to Ground

1.Disconnect the serial link jumper.

2.Remove the override switch from the dash.

3.Disconnect the cab harness from the switch.

4.Connect the serial link jumper into the serial communication port.

5.Measure the voltage from J1B module connector pin Y2 (the Auxiliary No. 1 output line) to a good ground.

If 12 volts are present, there is a short to voltage between the override switch connector and the J1B module connector. Locate and repair the short. Retest to be sure the problem has been corrected.

If 12 volts are not present, replace the override switch and retest the fan drive.

Test 512

Testing the system when cold

1.Reconnect the J1A, J1B and J2 connectors.

2.Reconnect the engine harness to the fan clutch solenoid connector.

3.Start the engine. Turn off the air conditioning. Allow the air pressure to build up to at least 90 psi.

4.When operating conditions are such that the fan is OFF or should be OFF, stop the engine.

Test 1024

Testing the system when hot

1.View the Customer Data Table in V-MAC II to determine the temperature at which the fan should engage.

2.Start the engine. Turn off the air conditioning. Allow the coolant temperature to increase.

3.Monitor the engine temperature with a diagnostic tool and with the dashboard temperature gauge. If the two temperatures do not agree, there may be a problem with the gauge which makes it appear that the fan is not turning on at the proper time.

4.Once the engine temperature exceeds the customer’s setting, the fan should turn ON.

5.After the fan has turned ON, the fan should turn OFF approximately 7°F (4°C) below the engagement temperature.

If the fan engages and disengages at the proper temperatures, there is not a problem with the electrical and pneumatic portions of the fan control system.

If the fan does not engage and disengage at the proper temperatures and the engine temperatures agree, replace the V-MAC II module. Retest to be sure the problem has been corrected.

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