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42
Table 29 — Troubleshooting (cont)
FAULT
COOLING HEATING
CHECK
POSSIBLE CAUSE
SOLUTION
No compressor or fan
operation
X
X
Power LED on
Bad thermostat
connection / faulty
thermostat
Check thermostat and wiring. Check unit terminal
block for 24 VAC between " Y" and " C" and " G" and
" C" .
Power LED off
Low or no supply power
Ensure that the supply voltage to the unit is with in the
range shown on the unit data plate.
Faulty control transformer
Check for 24 VAC between " R" and " C" on the unit ter-
minal block. For 75 and 100 VA transformers, check
that the transformer circuit breaker has not tripped.
Check low voltage circuit for overload conditons or
short circuits before replacing the transformer.
No fan operation - PSC
motor
X
X
Fan relay
energized
Faulty motor
Check supply voltage from the fan relay to the motor.
Check that all motor wires are secure. With power off
spin the motor shaft - noise, resistance or uneven
motion can be signs of motor failure.
Fan relay not
energized
No fan operation signal
Check for 24 VAC across the fan relay coil. Check all
wiring connections.
Bad fan relay
If the relay coil is energized but the relay does not pull
in, check the resistance across the relay coil - an open
circuit is an indicator of a faulty relay.
No fan operation -
constant torque motor
X
X
No fan operation signal
Check for 24 VAC between " G" and " C" . Check all wir-
ing connections.
Loose wiring
Check all wiring connections at motor and control box.
Faulty motor
Check supply voltage to the motor. Check that all
motor wires are secure. With power off spin the motor
shaft - noise, resistance or uneven motion can be
signs of motor failure.
No fan operation -
constant airflow motor
X
X
No fan operation signal
Check for 24 VAC between " G" and " C" . Check all wir-
ing connections. Make sure that the thermostat con-
nection plug is securely connected.
Loose wiring
Check all wiring connections at motor and control box.
Check that power and control harnesses are securely
connected.
Interface board problems
Make sure that the interface board is not damged and
that all DIP switches are in the proper configuration
(refer to the blower performance tables).
Faulty motor
Check supply voltage to the motor. Check that all
motor wires are secure. Move the " TEST" DIP switch
to " ON" and the other switches to " OFF" on the
" ADJUST" switch block on the interface board - the
motor should run at 70% torque whrn " G" is called.
With power off spin the motor shaft - noise, resistance
or uneven motion can be signs of motor failure.
Unit not shifting into
cooling
X
Reversing valve
solenoid energized
Faulty solenoid
Check that the reversing valve solenoid is receiving 24
VAC. If so, check the resistance of the solenoid - an
open circuit may indicate a burned out solenoid.
Reversing valve
solenoid not
energized
Miswired/faulty
thermostat
Check that the reversing valve theromstat wire is con-
nected to the " O" terminal of the thermostat. Check for
a contact closure between " O" and " R" .
Loose wire on " O"
terminal
Check that the wires from the thermostat to the unit
are securely connected and that the wires from the
electrical box to the reversing valve are connected.
Excessively cold supply
air temperature in
cooling or excessively
hot supply air
temperature in heating
X
X
Reduced airflow
Dirty Filter
Replace filter.
Fan speed too low
Consult blower performance table and increase fan
speed if possible.
Excessive duct pressure drop Consult blower performance table and increase fan
speed if possible.
Excessively warm
supply air temperature
in cooling and/or
excessively cool air in
heating
X
X
Airflow too high
Fan speed setting too high
Consult blower performance table and reduce fan
speed if possible.
High or low water
temperature
Inlet water temperature out of
range
Check unit capacity vs. water temperature.
Air leakage
Leaky ductwork
Inspect ductwork.
Loss of refrigeration
capacity
Low refrigerant
Check refrigerant pressures with gage set.
High humidity
X
Airflow too high
Fan speed setting too
high
Consult blower performance table and reduce fan
speed if possible.
Loss of refrigeration
capacity
Low refrigerant
Check refrigerant pressures with gage set.
Short cycling
Unit oversized
Check unit performance against building load calcula-
tions.
Poor thermostat location
Make sure that thermostat is not located by a supply-
air duct.