why your heat pump is blowing cold air

Your heat pump is blowing cold air and you’re not sure what’s causing it? This is an integral part of your heating system and when it fails, it leaves you in the cold. There are many reasons why this can happen.

You can solve some of these issues on your own with troubleshooting. Others may need your HVAC specialist for service.

1) The Heat Pump is in Defrost Mode

It’s normal for your heat pump to go through a defrost mode to heat the outside coil from freezing. When your heat pump starts a defrost mode, it will momentarily reverse its operation to go through a cooling cycle. This action pushes the warm air through the outdoor coil, defrosting it.

  • If you see frost or ice on your outdoor coil, it means your defrost cycle isn’t working well and needs maintenance. 
  • Possible causes include a faulty thermostat, damage to the outdoor coil, faulty wiring or equipment. 

2) Incorrect Thermostat Settings

Your thermostat is an integral part of your heating and cooling system. When you set your thermostat to “on”, it means the fan will continue blowing even after the heat turns off. This would result in pushing cool air through your home instead of heating the air.

  • Ensure you have your thermostat setting to “auto” so that the blowers turn on at the same time as your heat turns on. 

3) Your Heat Pump Has a Refrigerant Leak

With a heat pump, refrigerant plays a crucial role in the heat exchange process. Leaks in these lines can cause problems including less efficient heat exchange, unbalanced refrigerant charge and outdoor coil freezing.

  • Refrigerant in a heat pump absorbs heat from outside during a heat cycle. A refrigerant leak reduces the amount of refrigerant available to warm the air. This diminishes the heat exchange efficiency of the system.
  • Imbalance in refrigerant charge from a leak will not provide enough charge to the heat pump. This impacts the efficiency of the heat pump in transferring heat. 
  • In a heat pump, the refrigerant moves between the indoor and outdoor units. A refrigerant leak can disrupt this cycle and lead to issues such as ice collecting on the coil. 

4) A Dirty Outdoor Unit

A dirty outdoor unit can cause a multitude of issues with your heat pump. These will lead to operational failure or complete unit failure. Here are a few of the more common issues that arise with a dirty outdoor unit.

  • Reduced heat exchange efficiency happens when your heat pump’s coil is dirty. When dirt and debris cover the coils inside your heat pump, it hinders the heat exchange process. 
  • A buildup of grass, dirt and debris around your unit can cause restricted airflow. Restricted airflow can lead to a multitude of issues including overheating of components, increased energy consumption, and reduced airflow. 
  • If the outdoor unit becomes dirty, it hinders the heat exchange process. In humid conditions, ice may form on the coil of your heat pump. The compressor in turn will need to work harder to keep the space warm. 

5) The Circuit Breaker is Tripped

When your heat pump is blowing cold air and you find your circuit breaker has tripped, this often indicates an electrical issue. Some of the common issues include:

  • When a circuit breaker trips, this cuts off power to the heat pump as a safety feature. In return, this leads to the system blowing cold air. 
  • Modern safety features have the ability to shut down the heat pump when there is an electrical issue, such as a tripped circuit breaker. The lack of power prevents the heat pump from initiating the heating cycle, blowing cold air. 
  • An incomplete heating cycle happens when the breaker trips in the middle of a heating cycle. In this case, the system will start blowing cool air mid cycle.

6) Leaky Ductwork

In older homes, it isn’t uncommon to find leaky ductwork. Oftentimes, leaky ductwork can lead to the circulation of cool air in addition to many other HVAC problems.

  • When you have leaky ductwork, cool air from unconditioned rooms or the outdoors, make the warm air feel cool.
  • Leaky ductwork can also cause a loss of heat from entering intended rooms. This results in less than warm air entering your rooms.
  • Leaky ductwork can increase the workload on your heat pump. This adds to higher energy consumption and can potentially reduce the overall efficiency of the heat pump.

7) Issues with Reversing Valve

The reversing valve controls the direction of refrigerant flow. This determines if the system is operating on heating or cooling mode. Here’s how a reversing valve problem can lead to your heat pump blowing cold air.

  • The reversing valve is responsible for redirecting the flow of refrigerant between the indoor and outdoor cells. If this valve becomes stuck or broken, your heat pump may still blow cold air even when you are running your heat.
  • Sometimes this valve can get stuck between the two and releases a mixture of hot and cold air. 

8) A Dirty Filter

A dirty air filter can cause many issues with your heat pump, often leading to your unit blowing cold air.

  • When dirt and grime fill your filter, they block the airflow from entering your furnace and being warmed. This restricted airflow reduces the amount of warm air that passes through, leading to your unit blowing cool air.
  • A dirty air filter causes reduced airflow and this can lead to overheating your heat pump. When this happens, a safety mechanism is activated called the high limit switch. This will force the furnace burners to stop working, blowing cold air into your home. 
  • Ensure to replace your air filter regularly to prevent your furnace from overheating. 

9) Low Refrigerant Levels

Low refrigerant levels in the heat pump can cause several issues. For your heat pump to run efficiently, ensure there isn’t a leak in your refrigerant line.

  • The refrigerant is responsible for absorbing heat from the outdoor air during a heating cycle. If the refrigerant levels are low, there is not enough medium to effectively absorb heat from the air. This will make the heat pump struggle to produce heat and the air coming in will feel cooler than it should. 
  • If the refrigerant levels are low, the heat transfer efficiency decreases, delivering air that isn’t warm.
  • Overheating of the cooling compressor can also happen with low refrigerant levels. When the cooling compressor does not have an adequate amount of refrigerant, the compressor will overheat causing your system to blow cold air. 


If you are experiencing issues with your heat pump blowing cold air, call Schultheis Brothers, your HVAC specialist for a free evaluation. We are here to keep your home warm this winter.