31Service Manual – SC900 24 - Electrical System
Problem Cause Notes & Correction
No Scrub system, but
drive and vacuum
operational.
• No Brush
• No Solution
• No Detergent
• Drive active
• Vacuum active
K1 circuit fault The K1 circuit controls all of the scrub functions, and is related
to the low-voltage cutout feature, which is controlled by the
hour meter.
• Check the K1 relay:
− If the relay is open, either the relay is faulty, or the hour
meter is faulty.
− If the relay is closed, then the brush switch is faulty.
Hour Meter Failure If the hour meter does not provide “ground” to the K1 relay, it
will disable all scrub functions as though the battery voltage is
too low for operation
No Solution, but brush
motors run
Solution circuit or
optional module
The solution solenoid and optional detergent pump are
enabled only when the brush is active.
• For all models, make sure that the solution shutoff valve is
not closed.
• For non-EcoFlex models, make sure the shunt jumper
below the solution lever is in place. If so, then check the
solenoid.
• For EcoFlex models, if both solution and detergent
solenoids are non-functional, the module is likely faulty.
No Brush function, but
solutionows
Brush circuit failure Becausesolutionisowing,youcaneliminatetheK1andS4
circuits as a cause.
• If both brush motors are off, then the most likely cause is
the K2 power relay.
• Ifonlyonemotorhasfailed,rstcheckitscircuitbreaker,
and then check the motor. Swap the two motor connectors
to isolate whether it is before or after the connector.
No vacuum, but all
other systems function
Vacuum circuit If any other systems are running, then you know the KSI
circuit is functional. This leaves solely the vacuum circuit itself
as the cause.
• Check the vacuum switch at the squeegee lever
• Check the vacuum relay (K3)
• Check the vacuum breaker (CB4)
• Check the motor
Battery Testing
A battery problem is usually recognized by the machine operator as a decrease in the machine’s running
time. This condition is usually caused by one or more “dead cells” in the battery system.
There are 2 ways to nd a dead cell:
• Use a hydrometer to check the specic gravity (or “state of charge”) of the uid in each cell. A dead cell is
one that reads 50 points (or more) lower than the other cells.
• Use a volt meter to check the voltage of each battery. Look for a battery with a voltage that is 1 or 2 volts
less than the other batteries. Check under the following conditions:
– With the batteries fully charged,
– With the scrub and drive motors running,
– With the batteries discharged, but still above the voltage cutoff threshold.
If the batteries in the machine are more than 1 year old, it’s usually best to replace the whole set, rather
than replacing just one battery.
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