Bosch LV009 Installation And Maintenance Manual page 37

LV Heat Pump Series
Problem
No compressor operation
but fan runs
No compressor or fan
operation
No fan operation - PSC
motor
No fan operation -
constant torque motor
LV Heat Pump Series
UNIT TROUBLESHOOTING
Mode Check
No fault LED -
X X
contactor energized
Power LED on
X X
Power LED off
Fan relay energized
X X
Fan relay not
energized
X X
Possible Cause
Check for supply voltage at the load
Open compressor side of the contactor. For 3 phase
overload models check phase rotation and
Look for signs of heat on the wiring
insulation. Check that all wiring
Poor wiring connections
connections are secure and properly
Does compressor hum when power
windings using the values shown in
Burned out compressor
the compressor characteristics chart.
Note that the compressor must be
cool (70° F) when checking the
Bad thermostat Check thermostat and wiring. Check
connection / faulty unit terminal block for 24 VAC
thermostat between "Y" and "C" and "G" and "C".
ensure that the supply voltage to the
Low or no supply power unit is with in the range shown on
Check for 24 VAC between "R" and
"C" on the unit terminal block. For
75 and 100 VA transformers, check
that the transformer circuit breaker
Faulty control transformer
has not tripped. Check low voltage
circuit for overload conditions or
short circuits before replacing the
check supply voltage from the fan
relay to the motor. Check that all
motor wires are secure. With power
Faulty motor
off spin the motor shaft - noise,
resistance or uneven motion can be
Check for 24 VAC across the fan relay
No fan operation signal
coil. Check all wiring connections.
If the relay coil is energized but the
relay does not pull in, check the
Bad fan relay resistance across the relay coil - an
open circuit is an indicator of a faulty
Check for 24 VAC between "G" and
No fan operation signal
"C". Check all wiring connections.
Check all wiring connections at
Loose wiring
Check supply voltage to the motor.
Check that all motor wires are
secure. With power off spin the
Faulty motor
motor shaft - noise, resistance or
uneven motion can be signs of motor
Troubleshooting | 37
Action
voltage at all 3 phases.
torqued.
is applied? If not check the
resistance of the compressor
windings.
the unit data plate.
transformer.
signs of motor failure.
relay.
motor and control box.
failure.
8 733 905 683 (2016/09)