Why Does My Heat Pump Blower Run Continuously?

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It could be several issues. Perhaps the fan is broken, or it’s a thermostat issue. It might be easier to diagnose the problem if you understand how the AC and the fan, in particular, works.

The good news is that AC blower system issues are relatively easy to fix. Even if the fan is broken, you can replace it for under $30. So, let’s find out what could be causing your heat pump fan to run continuously.

How the AC/Heat Pump Fan Works

The blower system forms part of the indoor air handler – the component of the mini split that resides inside the house.

It has multiple functions. When the AC is in Heating Mode, the fan helps draw cold air into the air handler through the return vents and blows out warm air via the supply vents. It also ensures that the warm air reaches every corner of the room and that there’s even warm air distribution throughout the home.

The thermostat controls the fan, and although the fan often runs in tandem with the heat pump, it can also run independently, with the heat pump off. The latter usually happens when you set the heat pump to “Fan Only” mode. However, any time the heat pump is ON, the fan will also be ON.  

In many heat pumps, the blower is designed to run for a few seconds before actual heating begins and again for a few seconds after heating stops. It helps to get air flowing inside the room so that it’s easier to draw air from the room and circulate warm air back.

Running speeds vary. Indeed, some heat pump blower systems are designed such that the fan auto-regulates. It will automatically determine when it should run faster and slow down automatically when the heating load is lower. Otherwise, you need to select the run speed. Many heat pumps offer two or three fan speeds, i.e., low and high or low, medium, and high.

4 Reasons Why your Heat Pump Fan is Running Continuously?

As we’ve seen, the fan should only run when the heat pump is also running, when the unit is set to “Fan Only” mode, or for a few seconds before and after the heat pump goes off. If you notice that it’s running outside these settings, there could be a problem.

1. Incorrect fan settings

Before you jump into panic mode, you may want to check the settings on the thermostat. As mentioned earlier, the fan gets instructions from the thermostat. For example, if the thermostat says “run continuously,” the fan will run without stop.

Therefore, if the heat pump is off, but the fan keeps running, maybe the thermostat is set that way. This is often the case if you select “ON” for the fan section. The fan will keep running even when the AC is off – until you shut off the fan itself.

Solution: If you want the fan only to run when the heat pump is running, select the “AUTO” setting. Also, make sure always to check the fan setting before you begin heating or cooling.

2. The thermostat is broken

Since the thermostat controls the blower system, a broken thermostat can cause the fan to go rogue. Think about it this way – the thermostat tells the fan that the heat pump is running, thus alerting the fan to begin running too. When the heat pump goes off, it instructs the AC to go off too.

Now, imagine a scenario where the thermostat is broken. You might turn off the heat pump, but the broken thermostat may not pick up on the signal. Thus, it won’t alert the fan to go off too. Keep in mind that the fan is wired separately – which is why it can run even when the AC is off in “Fan Only” mode.

Solution: For thermostats that use batteries, replacing drained batteries can return the unit to regular operation. Otherwise, you need to call an HVAC professional or purchase a new thermostat.

3. It’s a blower relay switch malfunction

The blower motor relay is the electrical switch used to supply to the air conditioner’s blower motor. The blower motor pushes air through the vents to keep you warm in winter and cool in summer. The relay system controls how much current reaches the motor, directly impacting the motor’s speed and other operational parameters.

As such, a malfunctioned relay system can directly impact the fan. Although a broken relay switch will, in most cases, cause the fan to stop, a malfunction can also cause the fan to run non-stop.

Solution: Different things can go wrong that may impact the relay switch. However, all the issues can only be diagnosed and fixed by an HVAC technician. Don’t attempt a DIY.

4. It’s extremely cold outside

Heat pumps are often overwhelmed when it becomes too cold outside. Some will go off altogether when temperatures dip below 35˚F to 40˚F to prevent condensation inside the AC. At this point, many HVAC systems are designed to engage an auxiliary heat source, a stand-by electric heating mechanism, to continue providing the necessary heating.

However, problems sometimes arise when the transition from the heat pump to the electric heating isn’t seamless. This might leave the fan running even when the heat pump is no longer responsible for the heating process.

Solution: Since the setup that transitions heating from the heat pump to the auxiliary heater is complex and delicate, it’s best to call an HVAC technician.  

Regular Maintenance is Critical  

Ultimately, you’ll find that you can prevent most blower fan issues with regular maintenance. If you let an HVAC professional take a look at your heat pump immediately before the heating season, you can catch and fix issues such as damaged relay switches and a damaged thermostat early. The technician will also ensure that your auxiliary heating system is wired appropriately.

However, if the damage has already occurred, verify that you’ve selected the correct fan settings and that the thermostat is functioning normally. If the problem persists, switch off the heat pump and call an HVAC professional.  

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