Section 7

DIAGNOSTIC TESTS

TEST 39 - CHECK OIL PRESSURE SWITCH

DISCUSSION:

Also see “Operational Analysis” on Pages 18-23. The Low Oil Pressure Switch is normally-closed, but is held open by engine oil pressure during cranking and startup. Should oil pressure drop below a safe level, the switch contacts will close to ground the Wire 85 circuit. Engine controller board action will then initiate an automatic shutdown.

If the switch fails CLOSED, the engine will crank and start, but will then shut down after a few seconds.

If the switch fails OPEN, low oil pressure will not result in automatic shutdown.

Figure 7-46. – Oil Pressure Switch

PROCEDURE:

1.Check engine oil level. If necessary, replenish oil level to the dipstick “FULL” mark.

2.Set a VOM to its “Rx1” scale and zero the meter.

3.Connect the meter test leads across the switch terminals, with engine shut down. The meter should read “Continuity”. A small amount of resistance is acceptable.

4.Crank the engine. Oil pressure should open the switch contacts at some point while cranking and starting. Meter should then indicate “Infinity”.

5.If the contacts did not open in Step 5, remove the low oil pres- sure switch and connect an oil pressure gauge in it’s place. Start the engine and measure oil pressure. Pressure should be above 10 psi.

RESULTS:

1.In Step 3, if “Continuity” is not indicated, replace the switch.

2.If oil pressure checked good in Step 5, but Step 4 measured “Infinity,” replace the low oil pressure switch.

3.If oil pressure is below 10 psi, determine cause of low oil pres- sure. Refer to Engine Service manual No. 0E2081 for further engine service information. Verify that the oil is the proper vis- cosity for the climate and season.

4.If all steps check GOOD, go to Test 40.

TEST 40 - TEST OIL TEMPERATURE SWITCH

DISCUSSION:

If the engine cranks, starts and then shuts down, one possible cause of the problem may be a high oil tem- perature condition. Protective shutdown is a normal occurrence if the oil temperature switch exceeds approximately 270°F for gasoline units, or 284°F for LP units.

Figure 7-47. – Oil Temperature Switch

PROCEDURE:

1.Remove Wire 85 from Oil Temperature Switch terminal and start the generator. If engine starts and runs now, but shuts down when Wire 85 is connected to the switch terminal, the fol- lowing possibilities exist:

a.Oil temperature is too high.

b.The oil temperature switch has failed closed or is shorted to ground.

2.Remove the switch and place its sensing tip into oil (Figure 7- 48). Place a thermometer into the oil.

3.Connect the test leads of a VOM across the switch terminals. The meter should read “Infinity”.

4.Heat the oil. When oil temperature reaches approximately 270- 284°F., the switch contacts should close and the meter should read “Continuity”.

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Generac Power Systems 75, 55, 65 manual Test 39 Check OIL Pressure Switch, Test 40 Test OIL Temperature Switch
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65, 75, 55 specifications

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