Heat pump troubleshooting guides

49 guides. Heating, cooling and defrost problems on heat pumps. Each one lists the likely causes and what to check, in order.

All brands (15)

• 2 flashes: HPS open ≥6 s; 3: discharge >263°F; 4: discharge <90°F after 1 h; 5: defrost failure; 6: discharge sensor short; 7: outdoor sensor open/short; 9: bonnet sensor fail
  Possible causes and checks for: 2 flashes: hps open ≥6 s; 3: discharge >263°f; 4: discharge <90°f after 1 h; 5: defrost failure; 6: discharge sensor s
• Excess ice on outdoor coil
  Possible causes and checks for: excess ice on outdoor coil.
• Extremely high head pressure in heating (dual fuel)
  Possible causes and checks for: extremely high head pressure in heating (dual fuel).
• Insufficient heat in cold weather
  Possible causes and checks for: insufficient heat in cold weather.
• Liquid slugging / compressor damage in heating
  Possible causes and checks for: liquid slugging / compressor damage in heating.
• No mode change / wrong mode
  Possible causes and checks for: no mode change / wrong mode.
• Odour at registers (dirty sock)
  Possible causes and checks for: odour at registers (dirty sock).
• Poor heating but OK cooling (or vice-versa)
  Possible causes and checks for: poor heating but ok cooling (or vice-versa).
• Service problem analysis (Amana chart excerpt)
  Possible causes and checks for: service problem analysis (amana chart excerpt).
• Subcooling too high
  Possible causes and checks for: subcooling too high.
• Subcooling too low vs mfr target
  Possible causes and checks for: subcooling too low vs mfr target.
• TXV bulb/diaphragm failure
  Possible causes and checks for: txv bulb/diaphragm failure.
• Water-source: coil freezing
  Possible causes and checks for: water-source: coil freezing.
• Won't change mode / both coils same temperature
  Possible causes and checks for: won't change mode / both coils same temperature.
• Wrong superheat after line-set change; poor capacity
  Possible causes and checks for: wrong superheat after line-set change; poor capacity.

Carrier (7)

• Amber STATUS or green COMM light not on
  Diagnosing the outdoor AOC board from its two lights.
• Delay before the compressor restarts
  The outdoor unit waits before starting again - usually normal.
• Heat pump will not defrost - HK32EA defrost board
  Outdoor coil ices up and the unit never shifts into defrost.
• Noisy compressor or loud defrost shift - Carrier split systems
  Gurgling, rattling, hard starts, whistles or loud swoosh/groan when shifting in and out of defrost.
• Outdoor ECM fan not running - Carrier 25HNB9/24ANB1
  Compressor runs but the variable-speed outdoor fan stays off.
• Outdoor unit unresponsive after several faults
  After some combinations of earlier fault codes the outdoor unit can stop responding even though nothing is broken.
• Outdoor unit will not run - HK32EA defrost board heat pumps
  Thermostat calls but the outdoor unit stays off on heat pumps with HK32EA defrost boards.

Goodman (3)

• No heat - R-32 GLZS/ALZS heat pump
  Heat pump does not deliver heat in heating mode.
• Outdoor coil iced / no defrost - R-32 GLZS/ALZS heat pump
  Outdoor coil builds ice in heating and the unit does not go into defrost, or defrost does not end properly.
• Reversing valve not shifting - ComfortNet heat pumps
  Heat pump stays in one mode, or suction pressure/temperature is abnormally high because the valve is stuck between positions or leaking.

Gree (7)

• Compressor will not run - Gree ductless
  Outdoor fan may run but the compressor does not start.
• Louver will not swing - Gree ductless
  The horizontal louver does not move.
• Noise or vibration - Gree ductless
  Clicks, gurgles or rattles from the indoor or outdoor unit.
• Outdoor fan will not run - Gree ductless
  Outdoor fan does not turn while the unit is calling.
• Unit will not start - Gree ductless
  Indoor unit shows no lights, no beep, or the breaker trips at power-up.
• Water leaking from indoor unit - Gree ductless
  Water drips from the indoor unit or the line set.
• Weak cooling or heating - Gree ductless
  Unit runs but room temperature is not reached.

ICP (2)

• Comfort Alert module basics
  Green POWER = module powered. Red TRIP = Y1 call but compressor off. Yellow ALERT flashes a code (number of flashes, pause, repeat).
• Defrost not working - test the defrost board
  Time/temperature defrost board: interval 30/60/90 min (factory 90). Defrost thermostat closes at 32F (0C) and opens at 65F (18C). Defrost limited to 1

KeepRite (2)

• Forcing a defrost to test the board - KeepRite N4H4/R4H4/WCH4/NXH5
  Steps to force a defrost cycle and confirm the defrost board, thermostat and reversing valve work.
• Outdoor unit will not run or will not defrost - KeepRite heat pump defrost board (FAST 1173636/1177927/1190281)
  Checks on the time/temperature defrost board used in these heat pumps.

Lennox (4)

• Heat pump not defrosting / outdoor coil iced - Lennox EL16KP1 / ML14KP1
  Ice builds up on the outdoor coil in heating and the unit does not clear it, or defrost ends before the coil is clear.
• Low capacity or abnormal pressures - Lennox EL16KP1 / ML14KP1
  Unit runs but heats or cools poorly, or gauge readings do not match the normal operating pressures.
• Outdoor unit will not start - Lennox EL16KP1 / ML14KP1
  Thermostat calls for heat or cooling but the outdoor compressor and fan do not run.
• Two horizontal lines on display (soft disable) - Lennox communicating
  The control shows two horizontal lines on its 7-segment display (damper module or EIM: green LED 3 s on / 1 s off). The thermostat found a device it d

Mitsubishi (4)

• Indoor board LED1 and LED2 both off - no power
  Nothing on the indoor unit or remote works and both LEDs on the indoor control board are dark.
• Indoor board LED2 blinking - remote controller line problem
  LED2 on the indoor control board blinks. If LED1 blinks too, the indoor/outdoor wire is the problem; if LED1 is steady, look at the remote controller
• Indoor fan does not run
  The indoor blower will not turn. The fan motor is a DC motor fed about 310-340 V DC from the indoor board.
• PLEASE WAIT stays on, or an error shows about 2 minutes after power-up
  For about 2 minutes after power-up the remote shows PLEASE WAIT while the system starts - that is normal. If it is followed by an error code, or the s

Rheem (4)

• Heat pump will not defrost / incomplete or excessive defrost
  Demand defrost is built into the ICC. Defrost starts when coil is below 35°F, compressor has run at least 34 minutes with coil below 35°F and the algo
• Insufficient cooling / pressure problems
  Unit runs but capacity is low; use pressures to narrow down.
• Outdoor fan runs but compressor does not
  Compressor fails to start while the outdoor fan runs.
• Outdoor unit will not run
  Electrical checks for a heat pump that does not start.

Trane (1)

• Forcing a defrost - Trane 5TWR7
  Use to check defrost operation on the multi-speed heat pump.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.