Grundfos CR Series Installation And Operation Manual page 14

Diagnosing specific problems
Problem
The pump runs but at
reduced capacity or
does not deliver water
(continued)
Pump cycles too much
Fuses blow or circuit breakers
or overload relays trip
14
Possible cause
8. Incorrect drain plug installed.
9. Improper coupling setting.
1. Pressure switch is not
properly adjusted or is
defective.
2. Level control is not properly
set or is defective.
3. Insufficient air charging or
leaking tank or piping.
4. Tank is too small.
5. Pump is oversized.
1. Low voltage.
2. Motor overloads are set
too low.
3. Three-phase current is
imbalanced.
4. Motor is shorted or
grounded.
5. Wiring or connections
are faulty.
6. Pump is bound.
7. Defective capacitor
(single-phase motors).
8. Motor overloads at higher
ambient temperature than
motor.
Remedy
If the proper drain plug is replaced with a standard plug,
water will recirculate internally. Replace with proper plug.
Check/reset the coupling, see page 10.
Check pressure setting on switch and operation. Check
voltage across closed contacts. Readjust switch or replace if
defective.
Check setting and operation. Readjust setting (refer to level
control manufacturer's data). Replace if defective.
Pump air into tank or diaphragm chamber. Check
diaphragm for leak. Check tank and piping for leaks with
soap and water solution. Check air to water volume. Repair
as necessary.
Check tank size and air volume in tank. Tank volume should
be approximately 10 gallons for each gpm of pump
capacity. The normal air volume is 2/3 of the total tank
volume at the pump cut-in pressure. Replace tank with one
of correct size.
Install pressure gauges on or near pump suction and
discharge ports. Start and run pump under normal
conditions, record gauge readings. Convert PSI to feet
(Measured PSI x 2.31 ft./PSI = _______ ft.) Refer to the spe-
cific pump curve for that model, ensure that total head is
sufficient to limit pump delivery within its design flow
range. Throttle pump discharge flow if necessary.
Check voltage at starter panel and motor. If voltage varies
more than ±10%, contact power company. Check wire
sizing.
Cycle pump and measure amperage. Increase heater size or
adjust trip setting to a maximum of motor nameplate (full
load) current.
Check current draw on each lead to the motor. Must be
within ±5%. If not, check motor and wiring. Rotating all
leads may eliminate this problem.
Turn off power and disconnect wiring. Measure the lead-to-
lead resistance with an ohmmeter (RX-1). Measure
lead-to-ground values with an ohmmeter (RX-100K) or a
megaohm meter. Record values. If an open or grounded
winding is found, remove the motor, repair and/or replace.
Check proper wiring and loose terminals. Tighten loose
terminals. Replace damaged wire.
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.
Turn off power and discharge capacitor. Check with ohm-
meter (RX-100K). When the meter is connected to the
capacitor, the needle should jump towards 0 ohms and
slowly drift back to infinity ( ). Replace if defective.
Use a thermometer to check the ambient temperature near
the overloads and motor. Record these values. If ambient
temperature at motor is lower than at overloads, especially
where temperature at overloads is above +104°F (+40°C),
ambient-compensated heaters should replace standard
heaters.