Service Manual

Part Numbers
NN10520
Purpose
The oil pressure switch on the 724 turns on the hourmeter. This ensures
that the hourmeter is not accidentally left running.
How It Works
When the engine is not running, the switch is open. Once the engine has
been started, oil enters through a small hole on the threaded end. This
presses on a diaphragm which moves a switch contact on the dry side of
the diaphragm. When pushed far enough, the contacts close. Note: The
contact is adjustable so that the switching pressure can be varied. It is set
to close from the factory at 5 psi + 2 psi.
Testing
1. Disconnect the switch from the system.
2. Verify the conditions in the table.
3. If the switch is opening when the machine is idling, verify that you have
proper oil pressure at idle (consult your engine manual.) If so, slowly
rotate the adjusting screw on the back of the switch until the switch
just closes.
4. If the switch is operating intermittently, check for a loose electrical wire,
or an obstruction to the orifice on the threaded end of the switch.
Part Numbers
NN10813
Purpose
This switch is optional on the 200 series tractors and could be used to turn
on an hourmeter.
How It Works
When the engine is not running, the switch is open. Once the engine has
been started, oil enters through a small hole on the threaded end. This
moves the diaphragm which moves a switch contact on the dry side of the
diaphragm. When pushed far enough, the switch contacts close. Note:
The contact is adjustable by turning the small set screw at the base of the
terminal. It is set to close at 1 psi ± ½ psi from the factory.
Testing
1. Disconnect the switch from the system.
2. Verify the conditions in the table.
3. If the switch is opening when the machine is idling, verify that you have
proper oil pressure at idle (consult your engine manual.) If so, slowly
rotate the adjusting screw on the back of the switch until the switch
just closes.
4. If the switch is operating intermittently, check for a loose electrical wire,
or an obstruction to the orifice on the threaded end of the switch.
Switch
Oil Pressure
Engine Switch
No Oil Pressure Open
Oil Pressure OK Closed
Switch
Oil Pressure
Engine Switch
No Oil Pressure Open
Oil Pressure OK Closed
Glossary
GLOSSARY
Demystification Guide 3-33