MAINTENANCE MATTERS
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Keeping cool as your coach cools


Coaches have long been built with air-operated fan clutches to control the engine coolant fans. The correct functioning of the fans and clutches are crucial to the overall performance of your MCI motor coach. Our simple troubleshooting guide should help you better understand both the two- and three-speed fan clutch on your E4500 and J4500 motor coaches.

Maintaining your coach's cooling system contributes to the longevity of the vehicle. These components are all designed for many thousand miles of trouble-free operation, but if the coach stays in a continued overheating state, it causes accelerated wear on the engine and all cooling-system components. While the Horton fan clutches are air-operated, solving the air-related issues also requires understanding the electrical circuits that control the air system.

For CAT engines with three-speed clutches

In the event of a fan clutch failure, please verify that the following applications are functioning correctly:

  • The engine ECM supplies 12 volt signals to actuate air solenoids.
  • The brake solenoid (top solenoid when looking in engine remote j-box) is normally closed. Applying voltage will open the solenoid and supply air to the brake chamber.
  • The direct clutch solenoid (bottom solenoid when looking in engine remote j-box) is normally open. Applying voltage will close the solenoid and exhaust air from the direct chamber.
  • Pressure should never be applied to both the brake and direct inlets at the same time (one-second overlap during fan test switch engagement is normal).
  • ECM programming should never supply 12 volts to the brake solenoid, while not applying voltage to the direct solenoid — this condition would cause air to be supplied to both chambers.
  • There is a pressure switch (located in engine remote j-box) which senses pressure on the direct clutch inlet line.  When pressure is applied to the direct inlet, the pressure switch opens, thus closing the brake solenoid.
  • The pressure protection valve (located in engne remote j-box) is set to open at 120 psi and close at 103 psi (+/- 5 psi).
  • As a general check, solenoids should be quickly and completely opening, closing and exhausting air. When using the fan-test switch to engage from a brake application, air should be felt exhausting from the brake solenoid (through the black plastic tube) immediately as the test switch is actuated (~1 second lag acceptable.)
  • Pressure-protection valves are set to close at 90 psi on coach 62534 and prior.
  • Verify the compressor cutout pressure on coaches built prior to 64455 is 131 psi (+/-2), or have 137 psi (+/-2) effective with unit number 64455. Coaches with Bendix air dryers (cutout pressure is 125 psi) have an external governor. The cut-in pressure for this governor will always be 20 psi below the cut-out pressure — 131 psi cutout, 111 psi cut-in. Haldex air dryers have an internal governor that can also be calibrated.

For Detroit Diesel engines with two-speed clutches

  • The engine ECM supplies GND signals to actuate air solenoid.
  • The direct clutch solenoid (bottom solenoid when looking in j-box) is normally open. Applying GND will close the solenoid and exhaust air from the direct chamber.
  • The pressure protection valve (located in rear j-box) is set to open at 120 psi and close at 103 psi, +/- 5 psi. Pressure-protection valves installed on coach 62534 and prior were built with a valve set to close at 90 psi.
  • Air pressure greater than 100 psi should be supplied to the clutch at all times during actuation.
  • As a general check, the solenoid should be quickly and completely opening, closing and exhausting air.
  • Verify the compressor cutout pressure is 130 psi, 135 is acceptable. Coaches with Bendix air dryers have an external governor. The cut in pressure for this governor will be always 20 psi of below the cut-out pressure — 130 psi cutout, 110 psi cut-in. Haldex air dryers have an internal governor that can also be calibrated. A/C gauges can be used at the schrader valve on the inlet to the rear j-box to measure system pressure.

Reminder: On coaches with 3 speed clutch fans, the brake air line must be disconnected and capped, when the clutch fan is mechanically locked using two 5/16"x18x1 bolts. The alternate method is disconnecting the brake solenoid connector in the rear remote J box, then locking up the clutch mechanically. This can be used for a limited time period only.

For additional information please contact MCI's technical support at 800-241-2947 or reference service information bulletin 2980.

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