Carrier 50HQP072-120 specifications Unit Does Not Operate

Table 18 — Troubleshooting (cont)

	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			X	Reversing valve	Set for cooling demand and check 24-vac on RV coil and at control.
Cooling					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/		X	X	Dirty filter	Replace or clean.
Not Cooling or Heating
		X		Reduced or no airflow in	Check for dirty air filter and clean or replace.
Properly
				heating
					Check fan motor operation and airflow restrictions.
					High external static. Check duct design and downstream interference.
			X	Reduced or no airflow in	Check for dirty air filter and clean or replace.
				cooling
					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	Check location and for air drafts behind thermostat.
				located
		X	X	Unit undersized	Recheck loads and sizing check sensible cooling load and heat pump
					capacity.
		X	X	Scaling in water heat	Perform scaling check and clean if necessary.
				exchanger
		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	Check for dirty air filter and clean or replace.
				heating
					Check fan motor operation and airflow restrictions.
					High external static. Check duct design and downstream interference.
			X	Reduced or no water flow in	Check pump operation or valve operation/setting.
				cooling
					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	Bring return-air temperature within design parameters.
				in heating
			X	Scaling in water heat	Perform scaling check and clean if necessary.
				exchanger
		X	X	Unit overcharged	Check superheat and subcooling. Reweigh in charge.
		X	X	Non-condensables in	Vacuum system and reweigh in charge.
				system
		X	X	Restricted metering device	Check superheat and subcooling. Replace.
Low Suction Pressure		X		Reduced water flow in	Check pump operation or water valve operation/setting.
				heating	Plugged strainer or filter. Clean or replace.
					Check water flow adjust to proper flow rate.
		X		Water temperature out of	Bring water temperature within design parameters.
				range
			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		X		Too high airflow	Check blower.
Temperature in Heating		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.
	LEGEND
FP	— Freeze Protection
HP	— High Pressure
LED — Light-Emitting Diode
LP	— Low Pressure
RV	— Reversing Valve

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