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A04 Engine Low-Revolution Error
Error detection method
• When engine revolution speed drops to 700min
(complete combustion), an abnormal fl ag is set and the engine stops. An Engine Speed Too Low condition is
assumed when the error fl ag has stopped the engine 5 consecutive times in 1 hour.
Troubleshooting
1
1-1 Has the fuel gas pressure dropped? Is the fuel empty?
Fuel
2
Check
Measure actual revolution speed using a revolution meter. Are the
2-1
revolution
revolutions low?
speed
3
3-1 Is the throttle valve operating?
Mixer
4
Check the ignition coil, cam angle sensor, and crank angle sensor.
Ignition
Check the ignition coil → Remove the connectors from the ignition
pulse
coil one by one during operations. It is normal if changes in
4-1
operational status, such as lowered revolutions, occur.
Cam angle & crank angle sensors → Refer to A23 and A24 for
inspections.
5
Any poor connections, poor contacts or severed wires between the
Wiring
5-1
throttle (step motor) wiring and connector? (Wiring from outdoor main
board connector 6P (black) CN066 to throttle (step motor))
6
6-1 Measure compression (See A06 5-1).
Engine
Check 6-1 again after washing the valve and adjusting the valve
6-2
clearance. Any problem with compression?
6-3 Are spark emissions normal?
6-4 Inspect ignition plug (see A06 2-3)
Replace the ignition coil, cam angle sensor and crank angle sensor one by one to identify the
6-5
defective part.
6-6 Inspect the zero governor (see A06 3-1).
6-7 Is the ignition timing normal? (see A06 5-4)
7
Does the fuel regulating valve (step motor) coil resistance measure
Fuel gas
about 120Ω? (Disconnect relay connector 6P-6 and measure
7-1
regulating
between No. 1 (red) and No. 2/No. 3, and between No. 4 (orange)
valve
and No. 5/No.6.)
Is 4V DC being applied between the outdoor main board connector
7-2
6P (red) CN065 No. 5 and No. 1/No. 2 as well as between No. 3/No.
4 when the power is on (during positioning)?
8
Does the throttle (step motor) coil resistance measure about 120Ω?
Mixer
8-1
(Disconnect relay connector 6P-2, and measure between No. 1 (red)
and No. 2/No. 3, and between No. 4 (orange) and No. 5/No. 6.)
Is 4V DC being applied between the outdoor main board connector
6P (black) CN066 No. 1 (+) and No. 2 (-)/No. 3 (-) as well as between
8-2
No. 4 (+) and No. 5 (-)/No. 6 (-) when the power is on (during
positioning)?
● For work procedure for replacing outdoor main board, see "5. Reference Document".
● For board and Electrical Wiring Diagram, see Chapter 6.
• Outdoor main board: page VI-2
• Outdoor power board: page VI-3
• Converter board: VI-4
• Indoor control board for DC motor models: page VI-5
• Outdoor Unit Electrical Wiring Diagram: page VI-6
-1
or less continuously for 3 seconds during engine operation
IV–6
OK
2-1
NG Restore
Yes 3-1
No
4-1
Yes 6-1
No
5-1
OK
5-1
NG Restore
Yes Repair Wiring
No
8-1
OK
6-3
NG 6-2
OK
6-3
Replace engine
NG
head
Yes 6-6
No
6-4
OK
6-5
NG Replace
OK
6-7
NG Restore
OK
7-1
NG Adjust
OK
7-2
NG Replace mixer
Yes Replace mixer
No
8-1
Yes 8-2
No
Replace mixer
Yes Replace mixer
Replace the
No
outdoor unit's
main board
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Troubleshooting
