ECM Controlled Variable Speed Fan Clutch Group For 785B, 789B, And 793B Off-Highway Trucks{1356} Caterpillar

Off-Highway Truck/Tractor:

785B (S/N: 6HK523-UP)

789B (S/N: 7EK392-UP)

793B (S/N: 1HL412-UP)

Introduction

A variable speed fan clutch is available for the following sales models of Off-Highway Trucks:

• 785B

• 789B

• 793B

This variable speed fan clutch group is controlled by the engine Electronic Control Module (ECM). The variable speed fan clutch group is belt driven by the crankshaft pulley.

The fan clutch uses oil pressure to modulate engagement. The fan clutch allows uniform increases or decreases in the fan speed without any shock loads. The change in fan speeds is caused by permitting slippage of the oil cooled clutch plates.

The fan clutch will operate at the minimum speed when there is no oil pressure. 100 rpm to 300 rpm is the minimum operating speed. 800 rpm to 1000 rpm is the operating speed when a constant oil pressure is applied.

The variable speed control of the fan clutch is accomplished by a solenoid valve that supplies control pressure to the fan clutch. The solenoid is normally open. The solenoid normally bypasses the control oil back to the engine. A minimum temperature reading will cause the solenoid valve to modulate. A high pressure reading in the air conditioner will cause the solenoid valve to modulate. In both cases, oil pressure causes the fan clutch to engage.

Clutches with a standard drive and with an analog fan clutch were previously available. The standard drive can be converted to the ECM system. The analog fan clutch can also be converted to the ECM system.

Note: Do not perform any procedure that is outlined in this special instruction until this information is read and understood.

Reference: For additional information, consult the following publications.

• Service Magazine January, Page 14, "Modification Of Electronic Control Module (ECM) Controlled Variable Speed Fan Clutch Bracket-Shaft Assembly For Easier Fan Speed Sensor Removal"

• Service Manual, SENR8603, "Variable Speed Fan Clutch"

Description Of Change

The former fan clutch uses an analog system. The former clutch relies on a pulse width modulated signal from two temperature sensors in order to control the fan speed.

The analog system uses an aftercooler temperature sensor. The sensor can only turn on the fan to the FULL ON position. The ECM controlled fan clutch removes this sensor. The ECM controlled fan clutch replaces the old sensor with an improved sensor in order to improve control of the fan speeds. The fan clutch uses digital sensors to replace the pulse width modulated sensors. The ECM also uses two additional sensors in order to monitor the fan speeds. These sensors also control the fan speeds. These sensors are the speed timing sensor and the fan speed sensor.

The ECM system uses the coolant temperature sensor that is currently operating in the ECM. The analog system uses a different coolant temperature sensor. The old pulse width modulated sensor should be removed when the engine is updated to the variable speed fan clutch.

The aftercooler temperature sensor, the air conditioner switch, and the brake oil temperature switch must also be updated. The new components are listed in Table 1.

Illustration 1	g00290080
This is an Illustration of the 131-8681 Fan Control Group . (1) Refrigerant compressor. (2) 111-9560 Pressure Switch Assembly . (3) 9X-7378 Seal .

Illustration 2	g00290081
This is an Illustration of a typical Fan Control Group. (4) Aftercooler temperature switch. (5) 122-3192 Tube Assembly . (6) 102-7532 Electronic Control Group .

Illustration 3	g00290082
This is an Illustration of a typical Oil Cooler Lines Group. (7) 123-6710 Block . (8) 3E-5370 Temperature Sensor Group .

Illustration 4	g00290083
(9) 102-7532 Electronic Control Group . (D) Detail in Illustration 5

Illustration 5	g00290084
This is the detail (D) from Illustration 4. (9) 102-7532 Electronic Control Group .

The sensors provide digital signals to the ECM. The ECM varies the current level from 0.4 amperes to 1.9 amperes to the fan clutch solenoid valve. The current to the solenoid is high when the cooling requirements for the engine are at a minimum. The maximum current holds the solenoid valve in the bypass mode. As a result, oil pressure is not applied to the fan clutch. The 111-9560 Pressure Switch Assembly monitors the pressure in the air conditioner system. This switch assembly is required even if an air conditioner is not installed. An electric fault is generated without the switch. Operation of the air conditioner requires additional cooling. When the pressure that is in the air condenser exceeds 1585 kPa (230 psi), the switch closes. The ECM system then sends a low current to the solenoid for maximum fan speed. The temperatures from the sensors to the ECM are shown in Table 2.

Four thermostats that are located in the regulator housing are used in order to regulate the engine's temperature. When the engine coolant is below the operating temperature, the coolant bypasses the radiator. The coolant flows directly to the water pump. When operating temperatures have been achieved, the thermostats open and coolant flows to the radiator. As the temperatures rise, the ECM controls the fan clutch.

Reason For Change

The Advantages Of The ECM Controlled Fan Clutch Over the Analog Controlled Fan Clutch

The ECM controlled fan clutch provides an easier modulation than the analog controlled fan clutch. The ECM also allows a slower engagement of the fan. The slower engagement prolongs the life of the fan belts.

The advantage of the ECM controlled fan clutch also includes two additional sensors. The speed timing sensor supplies data to the control system. When the speed timing sensor senses an overspeed condition, the ECM will set the fan speed to a maximum. The fan speed sensor measures the actual fan speed. If the actual fan speed is within 50 rpm of the desired fan speed, the ECM will not adjust the current to the solenoid valve. If there is a problem with the fan speed sensor, a fault is generated. Current to the solenoid is then controlled based only on coolant temperature. At this point, the ECM does not measure the actual fan speed. The ECM does not adjust the current according to the sensor output.

Advantages Of The ECM Controlled Variable Speed Fan Clutch Over The Standard Fan Drive

The standard fan drive is continuously driven during the engine's operation. The variable speed fan clutch allows the fan to spin at low RPM levels when the fan is not active. As a result, less fuel will be consumed and more horsepower will be available to accelerate the engine up to the point when the fan is engaged.

During cold weather and idle conditions, a standard fan drive may overcool the engine. The overcooling is caused by drawing unneeded air across the radiator and the engine. In comparison, the variable speed fan clutch will draw very little air through the radiator when the air is not needed.

Modifications

Modification Of The Shaft Bracket For The Easier Removal Of The Fan Speed Sensor

When a variable speed fan clutch is installed, the fan speed sensor is not easy to access. The fan speed sensor may be difficult to remove. If a failure in the fan speed sensor occurs, the fan clutch must be removed in order to replace the sensor.

A modification can be made to the 109-8086 Shaft Bracket in order to allow the easier removal of the 125-1132 Fan Speed Sensor . This modification should be performed when the following conditions occur:

• A machine is being retrofitted from a standard fan drive to the ECM controlled variable speed fan clutch.

• A machine is being retrofitted from an analog controlled fan to the ECM controlled variable speed fan clutch.

• The modification is convenient on all machines that already have the ECM controlled variable speed fan clutch.

Procedure

Machine two radii to a length of 12.7 mm (0.50 inch) through the 109-8086 Shaft Bracket . See Illustration 6.

Illustration 6	g00290233
This is an Illustration of the dimensions that are needed in order to modify the 109-8086 Shaft Bracket . (A) 8.13 mm (0.320 inch). (B) 20.83 mm (0.820 inch). (C) 29.69 mm (1.169 inch). (D) 20.83 mm (0.820 inch). (X) 12.7 mm (0.50 inch) radius (two holes).

Modification Of The Adapter For The Easier Installation Of The Variable Speed Fan Drive

Note: This modification is valid only for the 793B Off-Highway Truck.

The installation of the variable speed fan drive group is complicated by the interference with the radiator. Use the following procedure to modify the 133-5908 Adapter (part of the 133-5969 Fan Drive Group ).

Illustration 7	g00290238
This Illustration identifies the 133-5969 Fan Drive Group components. (1) 133-5909 O-Ring Seal . (2) Hub Assembly. (3) 133-5908 Adapter . (4) 006-1800 Screws . (X) 12.7 mm (.50 inch) from the base of the shaft to the top of the shaft. (Y) 45 degrees 2.0 mm (.08 inch) chamfer.

Procedure

1. Remove the eight 006-1800 Screws (4) that fasten the 133-5908 Adapter (3) to the hub assembly (2). Retain the screws.

2. Remove the adapter from the hub assembly.

3. Remove the 133-5909 O-Ring Seal (1) from the adapter (3). Inspect the seal for damage. Retain the seal if the seal is acceptable for future use. If necessary, replace the seal.

4. Machine the shaft of the adapter until the crosshatched area that is shown in Illustration 7 has been removed. 12.7 mm (.50 inch) should remain.

5. Around the outside edge of the machined shaft, machine a chamfer (Y). Thoroughly clean the adapter.

6. Install the seal (1) in the adapter (3) .

7. Apply a light coat of 9S-3263 Thread Lock Compound on the threads of the eight 006-1800 Screws (4). Place the adapter (3) in position on the hub assembly (2) and install the eight screws (4). Tighten the screws to a torque of 242 ± 19 N·m (180 ± 15 lb ft).

Adaptability

The ECM controlled variable speed fan clutch went into production with these machine serial numbers:

• 785B ......................... 6HK523-UP

• 798B ......................... 7EK392-UP

• 793B ......................... 1HL412-UP

The variable speed fan clutch is adaptable to all Off-Highway Trucks that are equipped with the electronic unit injector system. Table 3 and 4contain the parts that are needed to change to an ECM controlled variable speed fan clutch.

Note: Some of the parts may be interchangeable with the former parts that are already installed on the machine. Verify the parts' requirements before you order any parts.

If an Off-Highway Truck is not equipped with ports in the front engine cover, the parts that are listed in Table 5 need to be ordered.

Reference: See Illustrations 8 and 9.

Illustration 8	g00290244
This is an Illustration of the 123-6919 Oil Lines Group . (1) 106-4685 Cover Assembly .

Illustration 9	g00290245
This is an Illustration of the 106-4685 Cover Assembly . (A) Rear View. (B) Side View. (C) Front View.

Reference: Consult the Service Manual, SENR8603, "Variable Speed Fan Clutch" for additional information.

Before the installation of an ECM controlled fan clutch in the 785B, 789B, and 793B Off-Highway Trucks, ensure that the Vital Information Management System configuration is compatible with the variable speed fan clutch. After the installation of the variable speed fan clutch, the settings for the ECM must be changed. The change is performed by using the Electronic Control Analyzer Programmer or by using the Electronic Technician service tools. The fan clutch is located in the "Read-Change Parameters" screen. The option should be set to the ON position.