Do I Need My AC Fan Speed Adjusted?

Unless your HVAC has a variable-speed blower fan, it will always circulate air throughout your home at the same rate of speed. This rate is determined by how fast the blower fan in your air handler spins. Although the fan only spins at one speed, most units still allow you to adjust the speed to be faster or slower. When you adjust the fan speed, it changes the airflow rate and will allow you to cool the home slower or more quickly.

Changing the fan speed is usually not necessary and can potentially create issues with your AC system’s performance. Nonetheless, there are situations where adjusting the fan speed can help improve home comfort. Let’s now take a look at the effect that fan speed has on your AC system and the reasons why you might need to have it adjusted.

Fan Speed and Airflow Rates

To work efficiently, air conditioning systems need to circulate so many cubic feet of air per minute. The exact volume required is determined by the size of the AC unit. The general rule is that the blower fan needs to circulate between 350 and 400 cubic feet of air per minute for each AC ton. A 3-ton AC requires 1,050 to 1,200 CFM, a 4-ton unit needs 1,400 to 1,600 CFM, etc.

The speed of the blower fan determines how much air volume the system moves. If the speed is set to high or too low, the air volume will also be too high or too low for the system to function properly. Setting the fan speed too low will usually cause the evaporator coil to freeze. If the fan speed is too high, it can cause the AC condenser to short-cycle or turn on and off constantly. This puts a huge amount of stress on the unit and also results in greatly increased energy costs.

Reasons the Speed of an AC Fan May Need to Be Adjusted

If your AC seems to run constantly and it takes hours for it to cool your home to the desired temperature, there is a chance that your fan speed is set too low. Setting the fan speed to higher will speed up the rate at which the system cools since it will circulate more cold air at a time.

However, the primary reason that an AC fan may need to be adjusted is due to high indoor humidity. High humidity can be a major issue in Puyallup due to our rainy, muggy weather. Your air conditioner helps to combat against high humidity by absorbing and removing moisture from inside the home.

If it only takes your air conditioner a few minutes to cool your home each time it runs, it won’t be able to have much of an effect on indoor humidity. The system obviously only absorbs moisture when the fan and condenser are both running.

This is why you should never leave your fan on when the AC isn’t running. If you do, it will cause the moisture on the evaporator coil and in the condensate drain system to evaporate again. This means that the fan will then start pumping humid air throughout the house.

The more your AC runs, the more humidity it will remove from the air. This is why in humid climates it is usually recommended that the system runs at 350 CFM per AC ton. By slowing the fan speed, you will also slow the rate at which the system cools. This means it will take longer for your AC to cool the home to the set temperature. As a result, the system will remove far more moisture to prevent issues with high indoor humidity.

In dry climates, your AC shouldn’t have any issues if the fan runs at a higher speed since there will be less moisture for the system to deal with. In this situation, running the fan at 400 CFM per AC ton is great because it will cool your home faster thus minimizing the amount of time the system runs and reducing your energy costs.

How to Adjust the Fan Speed on an AC System

If you suspect your AC fan needs adjusted, you will need to hire an AC technician to do this for you. Adjusting the fan speed involves rewiring the fan. If not done properly, you could burn out the fan motor. The fan will typically have three color-coded wires that correspond to low, medium and high speed.

The color-coding system is different for each manufacturer. Without proper training, it is virtually impossible to know which wire corresponds to which speed. It also requires specialized equipment to measure the airflow rate, which is necessary to determine whether your fan speed needs adjusted in the first place.

If you’re experiencing any issues with high humidity or you have any issues keeping your home cool, the certified technicians at Puyallup Heating & Air Conditioning service and repair all brands and models of AC units and blower fans. Should an emergency arise, we are available 24/7. We also install furnace, central AC systems and other HVAC equipment. To schedule a diagnostic test for your AC system, give us a call today. We service the greater Puyallup area.