49
Table 18 — Troubleshooting (cont)
LEGEND
FAULT
HEATING
COOLING
POSSIBLE CAUSE
SOLUTION
Only Compressor Runs
X
X
Thermostat wiring
Check G wiring at heat pump. Jumper G and R for fan operation.
Check Y and W wiring at heat pump. Jumper Y and R for compressor
operation in Test mode.
X
X
Fan motor relay
Jumper G and R for fan operation. Check for line voltage across BR
contacts.
Check fan power enable relay operation (if present).
X
X
Fan motor
Check for line voltage at motor. Check capacitor.
Unit Does Not Operate in
Cooling
X
Reversing valve
Set for cooling demand and check 24-vac on RV coil and at control.
If RV is stuck, run high pressure up by reducing water flow and while
operating engage and disengage RV coil voltage to push valve.
X
Thermostat setup
Check for ‘O’ RV setup not ‘B’.
X
Thermostat wiring
Check O wiring at heat pump. Jumper O and R for RV coil.
Insufficient Capacity/
Not Cooling or Heating
Properly
X
X
Dirty filter
Replace or clean.
X
Reduced or no airflow in
heating
Check for dirty air filter and clean or replace.
Check fan motor operation and airflow restrictions.
High external static. Check duct design and downstream interference.
X
Reduced or no airflow in
cooling
Check for dirty air filter and clean or replace.
Check fan motor operation and airflow restrictions.
High external static. Check duct design and downstream interference.
X
X
Leaky ductwork
Check supply and return-air temperatures at the unit and at distant
duct registers if significantly different, duct leaks are present.
X
X
Low refrigerant charge
Check superheat and subcooling.
X
X
Restricted metering device
Check superheat and subcooling. Replace.
X
Defective reversing valve
Perform RV touch test.
X
X
Thermostat improperly
located
Check location and for air drafts behind thermostat.
X
X
Unit undersized
Recheck loads and sizing check sensible cooling load and heat pump
capacity.
X
X
Scaling in water heat
exchanger
Perform scaling check and clean if necessary.
X
X
Inlet water too hot or cold
Check load, loop sizing, loop backfill, ground moisture.
High Head Pressure
X
Reduced or no airflow in
heating
Check for dirty air filter and clean or replace.
Check fan motor operation and airflow restrictions.
High external static. Check duct design and downstream interference.
X
Reduced or no water flow in
cooling
Check pump operation or valve operation/setting.
Check water flow adjust to proper flow rate.
X
Inlet water too hot
Check load, loop sizing, loop backfill, ground moisture.
X
Air temperature out of range
in heating
Bring return-air temperature within design parameters.
X
Scaling in water heat
exchanger
Perform scaling check and clean if necessary.
X
X
Unit overcharged
Check superheat and subcooling. Reweigh in charge.
X
X
Non-condensables in
system
Vacuum system and reweigh in charge.
X
X
Restricted metering device
Check superheat and subcooling. Replace.
Low Suction Pressure
X
Reduced water flow in
heating
Check pump operation or water valve operation/setting.
Plugged strainer or filter. Clean or replace.
Check water flow adjust to proper flow rate.
X
Water temperature out of
range
Bring water temperature within design parameters.
X
Reduced airflow in cooling
Check for dirty air filter and clean or replace.
Check fan motor operation and airflow restrictions.
High external static. Check duct design and downstream interference.
X
Air temperature out of range Too much cold vent air. Bring entering air temperature within design
parameters.
X
X
Insufficient charge
Check for refrigerant leaks.
Low Discharge Air
Temperature in Heating
X
Too high airflow
Check blower.
X
Poor performance
See ‘Insufficient Capacity’ above.
High Humidity
X
Too high airflow
Check blower.
X
Unit oversized
Recheck loads and sizing check sensible cooling load and heat pump
capacity.
FP
—
Freeze Protection
HP
—
High Pressure
LED —
Light-Emitting Diode
LP
—
Low Pressure
RV
—
Reversing Valve
