Which Way Should An AC Condenser Fan Spin?

Dennis Howard
by Dennis Howard

You may notice that the AC in your home is not cooling as well as you think it should. The filters are new, the evaporator coil is clean, and the blower fan is working as well as ever. Inspecting the condensing unit outside leads you to a question. Which way should the fan on the condensing unit spin?

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In general, the fan that moves air over the coils and around the compressor of the condensing unit should spin clockwise. Most condensing unit fans are designed to pull air through the coils and up out of the condensing unit. A fan spinning counter-clockwise affects the unit’s efficiency, overheating, and leads to eventual failure of the condensing unit.

There are several reasons the fan on the condensing unit spins counter-clockwise. If the fan motor was recently replaced, the wiring might have been performed incorrectly. In some instances, if the fan motor is starting to fail, it may begin to run in the wrong direction. A bad fan motor starting capacitor may also cause a condensing fan motor to run backward. You must diagnose and repair the problem in any case.

Why Does it Matter Which Way the Fan Turns on The Condensing Unit?

If the fan on your AC condensing unit runs backward, it is a sign that something significant is wrong with the system. If the problem is ignored, it can lead to more significant and costly repairs further down the line. The cooling fan on the AC condensing unit performs several vital functions that can be compromised if the fan doesn’t perform up to specification.

Air Movement is Critical for the Performance of your AC Condensing Unit

Fans are designed to move air. The fan blades on your AC condensing unit are engineered to operate when they turn in a specific direction. If the fan blades turn in the wrong direction, the amount of air moved through the condensing unit is significantly reduced. Less air movement through the condensing unit and across the coils can lead to many other problems.

Air Circulation Direction Through the Condensing Unit Matters

AC condensing units are carefully engineered pieces of equipment. The components inside the condensing unit are designed to work together. The way air flows over the condensing coils and through the unit is another design feature.

Most AC condensing units pull air through the coils first and then around the compressor and other components. This is a matter of efficiency since the cooler the air moving over the coils, the greater the unit’s cooling efficiency. If the air flows backward and moves over the compressor and motor first, it will be warmer and less efficient at cooling the refrigerant gas.

Component Failures Can Result from Overheating

Failures may result if there is insufficient air circulation around the compressor and other parts of the AC condensing unit. Keeping these critical components operating at the proper temperature is necessary to ensure their continued operation.

If the compressor and coils don’t get enough air movement, they begin to work harder to perform their jobs. As they work harder, they generate more heat which compounds the problem. In extreme situations, the compressor may fail due to overheating, leaving you with a more costly repair.

If the AC Condensing Unit is Working Harder, Your Electric Bill Will Be Higher

The harder your condensing unit must work to cool your home, the more electricity it uses. You will notice this change on your electric bill with time. Most of us are sensitive to the financial side of running our homes. It is expensive enough to keep a modern home operating. No one wants to add to the cost of keeping their home cool and comfortable. It pays, in the long run, to make sure your AC condensing unit is operating at peak efficiency.

Why Would Cause the Condensing Fan to Run Backwards?

The fan on your condensing unit can begin to run backward for several reasons. Some of these causes are relatively easy to diagnose. Others may take a service call from an HVAC technician to remedy. In any case, you must tend to this problem quickly to ensure your HVAC system works at its intended efficiency.

You May Have an Improperly Installed Fan Motor

If you have recently had a new fan motor installed on your AC condensing unit, the installer may have wired the motor wrong. Most condensing unit fan motors are designed to only run in one direction. However, many replacement motors are multi-directional. They can be wired to run in either direction.

These multi-directional motors can be confusing to install. Most of these motors come with a wiring schematic showing how the wires can be connected for different operations. These motors may even include different rotation speeds depending on which wires are used.

If a new condensing unit fan motor has recently been installed, ask the HVAC tech or installer to visit and check the system operation. The fix is as simple as changing the connection on two wires in many instances. However, we don’t recommend that most homeowners attempt this repair.

The Fan Motor May be Failing

Fan motors, just like any other piece of electrical equipment, have a limited life expectancy. If you think about where and how the fan motor on your condensing unit lives, you can understand the situation. The fan motor lives in a hostile environment, to say the least.

The fan motor on the condensing unit is exposed to the weather. Most fans are at the top of the condensing unit. This position exposes the motor to all the inclement weather that comes along. The fan motor must endure rain, sleet, and snow, not to mention sprinklers.

As the fan motor on your condensing unit ages, it will eventually fail. This is normal and should be expected. These failures can occur in different ways. One of the ways is an internal wiring failure that can cause the fan to run backward. We suggest that you call your HVAC technician to inspect, test and replace the fan motor if necessary.

A Bad Starting Capacitor Maybe At Fault

Most condensing units have a starting capacitor that helps the compressor begin operation. This starting capacitor may also supply electricity to the fan motor. If the starting capacitor is faulty, one symptom may be a condensing fan that runs backward.

You may also notice that the compressor has a harder time starting as it comes on. Symptoms that the starting capacitor is faulty may be more noticeable dimming of the lights in your home when the compressor starts running.

Starting capacitors are relatively easy to replace. However, starting capacitors are very specific to the condensing unit. You should only replace the starting capacitor with the exact same type. If you get the wrong capacitor, the condensing unit may not function, or you can damage the compressor. We recommend that you contact a qualified HVAC technician to test and replace the starting capacitor if necessary.

How Does The Condensing Unit Work?

The condensing unit is the heart of your AC system. It is connected to the evaporator coils inside your home’s air handling system by two tubes. The condensing unit is designed to remove heat from the air in your home and transfer it outside.

This heat transfer is accomplished using a refrigerant gas/liquid pumped through the condensing unit’s system. It is important to understand the parts and terminology of your HVAC system to grasp how the colling happens.

What are the Parts of a Condensing Unit?

Most condensing units consist of only a few parts. Other essential pieces to the system reside in your home and connect to the condensing unit. In general, these are the parts you will find in your AC condensing unit.

  • A Compressor – The refrigerant gas in your AC system is converted to liquid form in the refrigerant lines by the compressor. The liquid refrigerant is then sent to the evaporator coil of your HVAC system, where it is allowed to expand. This expansion of the liquid into a gas absorbs heat from the air in your home as it blows over the evaporator coil.
  • The Condenser Coils – As the gaseous refrigerant returns to the condensing unit, it passes through the coils surrounding the condensing unit. The fan on the condensing unit pulls outside air over these coils to cool the gaseous refrigerant before returning to a liquid state.
  • The Evaporator Coil – Inside your home somewhere in the HVAC air handling system is another set of coils. The air inside your home is pushed over these coils. As the liquid refrigerant expands inside the coils, it becomes cold and absorbs heat from the air in your home, making it cooler as well.

If the fan on your condensing unit is not working or is running in the wrong direction, the refrigerant in the lines cannot cool properly. This causes the compressor to work harder to return the refrigerant to a liquid state. This reduces the efficiency of your HVAC system resulting in higher electric bills. Compressor failures are also common from overheating and overwork.

Keeping the Fan Turning in the Right Direction is Important

The fan on your condensing unit is an integral part of a complex system. If this fan is not performing its job, the entire system is in peril. You will certainly notice that your AC system is not cooling your home as well. You may not notice the extra work the condensing unit is performing. Eventually, this will become a problem as the compressor fails and higher electric bills result.

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Dennis Howard
Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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