Diagnosing Specific Problems - Grundfos CR Installation And Operating Instructions Manual

19. Diagnosing specific problems

DANGER
Electric shock
Death or serious personal injury
- Before starting any work on the product, make
sure that the power supply has been switched off
and that it cannot be accidentally switched on.
Problem
1. The pump does not run.
30
Possible cause
a) No power to motor.
b) Fuses blown or circuit breaker tripped.
c) Motor starter overload protection burned or tripped
out.
d) Starter does not energize.
e) Defective control devices.
f) Motor is defective.
g) Defective capacitor (single-phase motors).
h) Pump is blocked or seized.
Remedy
Check voltage to motor terminal box. If no
voltage to motor, check starter panel for tripped
circuits and reset circuits.
Turn off power and remove fuses. Check for
continuity with ohmmeter. Replace blown fuses
or reset circuit breaker. If new fuses blow or
circuit breaker trips, the electrical installation,
motor and wires must be checked.
Check for voltage on line and load side of
starter. Replace or reset burned motor
protection. Inspect starter for other damage. If
protection trips again, check the supply voltage
and starter holding coil.
Energize control circuit and check for voltage to
the holding coil. If no voltage, check control
circuit fuses. If voltage, check holding coil for
short circuits. Replace bad coil.
Check that all safety and pressure switches
function correctly. Inspect contacts in control
devices. Replace worn or defective parts or
control devices.
Turn off power and disconnect wiring. Measure
the lead-to-lead resistances with ohmmeter (RX-
1). Measure lead-to-ground values with
ohmmeter (RX-100K). Record measured values.
If an open or grounded winding is found, remove
motor and repair or replace it.
Turn off power and outlet capacitor. Check with
ohmmeter (RX-100K). When the meter is
connected to the capacitor, the needle should
jump towards 0 ohms and slowly drift back to
infinity (h). Replace capacitor if defective.
Turn off power and manually rotate pump shaft.
If shaft does not rotate easily, check coupling
setting and adjust as necessary. If shaft rotation
is still tight, remove pump and inspect.
Disassemble and repair the pump.