Cummins/Onan 750 DFZ Generator Set

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Wrench

1. Operate Phase Selector switch to read generator output current and voltage.
2. Insert a screwdriver into the Voltage Adjust R21 potentiometer on the control front; loosen the locking nut with a wrench.
3. While observing the voltmeter, slowly turn the screwdriver clockwise to increase or counterclockwise to decrease voltage; adjust to rated nameplate voltage.
4. Retighten the locking nut without changing the adjustment.
5. Operate Phase Selector switch to the Off position.

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Accurate 2% voltmeter

1. Open control panel doors, locate VRAS-2 (upper left), and locate terminal board TB1 and R82 potentiometer.
2. Connect an accurate 2% voltmeter to VRAS-2 terminal board TB1-2 and TB1-3 terminals.
3. While observing the voltmeter, insert a screwdriver into R82 potentiometer and slowly turn to increase or decrease voltage until adjusted to rated nameplate voltage.
4. Disconnect voltmeter from TB1 and close control panel doors.

1. Close main line circuit breaker and apply approximately 1/4 of rated load.
2. Make sure engine speed is constant.
3. Turn GAIN potentiometer clockwise slowly until engine speed is not constant.
4. Turn potentiometer counterclockwise until a constant speed is achieved.
5. Turn counterclockwise an additional 1/2 division.
6. Use SPEED ADJUST potentiometer for fine speed adjustments of less than ±100 RPM.

1. Turn idle speed potentiometer counterclockwise to its stop, then clockwise 10 turns.
2. Turn run speed potentiometer counterclockwise to its stop, then clockwise 10 turns.
3. Turn gain potentiometer fully counterclockwise.
4. Turn droop potentiometer fully counterclockwise for isochronous operation.
5. Turn droop screw to approximately 40 for 3 percent droop.
6. Turn droop screw to approximately 80 for 5 percent droop.

⚠ High voltages in the control present an electrical shock hazard which can cause severe personal injury or death.

Tools: Screwdriver, Wrench

1. Operate Phase Selector switch to read generator output current and voltage.
2. Insert a screwdriver into the Voltage Adjust R21 potentiometer on the control front; loosen the locking nut.
3. Turn screwdriver to set the adjustment screw to the mid-position and retighten the locking nut.
4. Open control panel doors, locate VRAS-2 (upper left), and locate R32 potentiometer.
5. While observing the voltmeter, insert a screwdriver into R32 potentiometer and slowly turn to increase or decrease voltage until adjusted to rated nameplate voltage.
6. Close control panel doors and operate Phase Selector switch to the Off position.

⚠ Ignition of explosive battery gases can cause severe personal injury. Do not smoke while servicing batteries.

1. For DFW/DFY use two 12-volt batteries; for DFZ use four 12-volt batteries.
2. Connect two batteries in series (negative post of first battery to positive post of second).
3. Connect positive battery cables before connecting negative battery cables to prevent arcing.
4. Connect negative cable to a convenient bolt on the engine; connection must be clean and paint free.
5. If an automatic transfer switch without a built-in charge circuit is used, connect a separate trickle/float charger.

⚠ Filters should be handled with care to prevent damage.

Tools: compressed air

1. Loosen the eight attaching bolts and lift off the air cleaner head.
2. Remove the air filter element from the filter housing.
3. Blow low pressure compressed air (30 psi/207 kPa) through element from the clean side.
4. Hold nozzle at least 1 inch (25 mm) away to avoid damaging the element.

Tools: compressed air

1. Unsnap four latches holding head, lift off head and remove filter element.
2. Remove and discard precleaner cartridge.
3. Blow low pressure compressed air through pleated paper cartridge from the inside.
4. Hold nozzle at least 1 inch (25 mm) away to avoid damaging the element.
5. Replace pleated paper cartridge at every fourth cleaning.

⚠ Do not use antifreeze with an anti-leak formula; the stop leak element can prevent or retard coolant flow through the filter.

1. Close the shutoff valve.
2. Unscrew the coolant filter and discard.
3. Apply a light coat of lubricating oil to the gasket surface.
4. Install new filter and tighten by hand until seal just touches filter head.
5. Tighten an additional one-half to three-fourths turn.
6. Open the shutoff valve.

⚠ Failure to remove AC power presents a shock hazard and can cause serious personal injury or death.

⚠ Contact with hot coolant can result in severe burns.

1. Remove AC power from coolant heater.
2. Allow heater to cool before proceeding.
3. Remove the head and valve assembly.
4. Clean any scale deposits out of the tank.
5. Remove heating element and scrape off any accumulated scale.
6. Restore AC power to heater after system has been filled with coolant.

⚠ Excessive air pressure while starting the water flow could split the radiator core. Apply air pressure gradually.

Tools: flushing gun, compressed air

1. Open upper and lower radiator hose connections and install the radiator cap.
2. Attach flushing gun nozzle to lower radiator hose connection and fill radiator with water.
3. Gradually apply air pressure to avoid damaging the core.
4. Shut off air and allow radiator to refill; repeat until water runs clean.
5. Remove thermostat to flush block; attach flushing gun to upper radiator hose.
6. Restrict lower hose opening until block fills; apply air pressure and force water out.
7. Replace thermostat and all hoses and refill cooling system.

Tools: compressed air

1. Remove wing nut, flat washer and rubber washer; lift cover away from filter assembly.
2. Lift out breather element, vapor element and gasket.
3. Clean all parts with approved solvent; dry with compressed air (30 psi maximum OSHA).
4. Inspect all parts, replace if necessary.
5. Reassemble filter assembly, replace cover and secure.