Troubleshooting Heat Pumps

Troubleshooting heat pumps and easy repair guide, when the heat pump does not cool or heat, makes a noise, freezes up, cycles or simply doesn’t work.

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The article about heat pumps troubleshooting covers the most common problems, causes and solutions found on residential air-source heat pumps. Keep in mind that any problem or maintenance that you are not comfortable doing, should be done by a professional. The heat pumps are complex HVAC devices that contain many components so for any problem there might be a variety of reasons with one or more elements involved.

Since the heat pumps are electro-mechanical devices, there will be two types of failures that can occur; electrical and mechanical, and for each category of problems different skills are needed for the successful and safe repair.

Electric problems are related to loose wires, broken connections, open, grounded or short circuits, fuses issues, problems with the controls and switches…

Good examples of the mechanical problems are; dirty heat exchanger coils and an obstructed air flow, refrigerant leak, burned out motors, stuck valves, loose elements, blade or belts, noise…

In this article:

Troubleshooting a heat pump that does not start up

  • Make sure that there is an electric power to the unit.
  • Ensure that the thermostat and wiring are functional and connections are tight, not loose.
  • The circuit breaker did not trip off.
  • Make sure there are no blown fuses.
  • The thermostat is set to the right temperature - not too low.
  • Seized blower motor.
  • Stuck fan relay.
  • Shorted controlled board.

Troubleshooting heat pumps when a compressor fails

The compressor is an electrical and mechanical device welded or hermetic enclosed. Mechanical problems are very hard to check and fix while electric side is easier. Most failures on the electric side are due to an open, grounded or short circuit. Other reasons include a wiring problem, seized motor or problems with the compressor run capacitor.

Compressor noise

As the compressor is the heart of the heat pump, and if it doesn’t run for any reason, there will be no heating or cooling, since the refrigerant won’t be running through the system. One of the first symptoms of the problem is the compressor noise – a noise level that is higher than usual. Check out how to fix the noisy compressor problem.

Hard starting compressor motor

The cause of the hard starting compressor motor is due to the very low voltage caused by the home wiring issues, overloaded breaker box or short in the line. This will cause motor to run with difficulties.

Cooling issues

The most common cooling issues are as follows:

  • No cooling
  • Insufficient cooling
  • Too much of a cooling – fan is blowing cold air

Heating issues

The most common heating issues are as follows:

  • No heating
  • Insufficient heating
  • Too much of a heating

Ice build-up

One of the most common reasons for the ice build-up on the outdoor unit of the heat pump is the cold freezing weather, but this is not a big problem as long as it is maintain properly and because the ice will melt when the defrost mode kicks in. The real problem is icing up and when the unit is not defrosting. Causes of the defrost malfunction are faulty elements such as relays, controls, sensors or reverse valve. Also, if the unit cannot achieve set temperature for the correct defrost, check the outdoor fan for an obstruction or make sure that the refrigerant is not leaking and is on the proper level.

Tips: Proper defrost condensate must be provided. The unit should be installed on the platform (or adequate elevation) to allow drainage, otherwise in might get trapped.

Troubleshooting a heat pump when it does not operate in the heating mode

  • Problems with the outdoor fan.
  • The air flow rate is too low.
  • The air filter needs replacement.
  • Refrigerant over-charge.
  • Sticking reversing valve.
  • Problems with the compressor.

High heating cost

See all the reasons mentioned above where the heat pump does not operate in the heating mode. Also check for:

  • Improper control settings.
  • Thermostat tampering (frequent rising and lowering of space temperature).
  • Low supply air temperature at grilles.
  • Characteristics of the heat pumps.
  • Check out indoor airflow rate which might be too excessive.
  • The unit might be over-sized.
  • If the heat pump is over-sized this will result in short cycles, lower efficiency and ability to dehumidify, and it will shorten unit's and element's life.

Troubleshooting reversing valve

Reversing valve in heat pumps is used to change the flow direction of the refrigerant and therefore make switching between heating and cooling mode; troubleshooting heat pumps that include only the reversing valve fix is easy.

The most common problem with the reversing valve is the solenoid coil failure and when the valve is stuck in the heat or cool mode, or somewhere in between.

To solve the problem with the solenoid, check the voltage to see is the coil short out or open. This eliminates problems with the wiring. Solenoid can also be easily replaced.

If the valve is stuck, repair is hard and it requires replacement.

As it begins or ends defrost, when the valve reverses, the pressure in the system equalizes making the “whooshing” sound, which is normal. Also an indication that the reversing valve operates normally is very similar inlet and outlet temperatures on the appropriate line.

Checking the crankcase heater

Heat pumps utilize the crankcase heater to keep the compressor oil warm and prevent the liquid refrigerant getting into the compressor causing the damages. As it is powered by a high-voltage power, troubleshooting heat pumps with such a problem should be done with caution – simply apply voltmeter to see if the crankcase heater has power. Or, you can disconnect the power and heater leads and check with ohmmeter – look for an open circuit or resistance. Change the heater if an open circuit is found.

Time-Delay Relay – TDR

Time-Delay relay is a 24v device that allows blower to run some time even after thermostat is satisfied, so residual cooling is removed in coil. When the fan switch is set to AUTO and the blower runs continuously instead cycling off, the TDR element is faulty and must be changed.

Troubleshooting a heat pump noise

Buzzing, grinding, clicking, loud, gurgling, rattling, high-pitch, thumping, rumbling, hissing, whooshing, banging, humming, howling are just some of the heat pump noises and sounds that will be covered and explained, including the reasons for an easy troubleshooting.

As it can be seen from above, there are many problems that can occur to the heat pumps. Depending on the problem, troubleshooting heat pumps can be easy but also complicate and expensive. In order to reduce or even prevent future problems with this HVAC device, it is important to maintain the unit regularly - either by you or a professional.


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