Troubleshooting Guide: Outside AC Unit Fan Not Running but Inside Is

outside ac unit fan not running but inside is

If you’re facing the issue where the outside AC unit fan is not running while the inside one is operational, it could indicate various underlying problems. This guide will help you diagnose the issue outside ac unit fan not running but inside is and provide steps to resolve it effectively.

Common Causes of Outside AC Unit Fan Not Running

1. Electrical Issues

a. Tripped Circuit Breaker

One of the most common reasons for the outside AC unit fan not running is a tripped circuit breaker. Check the breaker box and reset the breaker associated with your outdoor unit.

b. Faulty Capacitor

The capacitor in your AC unit provides the initial electrical boost needed to start the fan motor. If the capacitor is faulty or worn out, it may not be able to start the fan motor.

2. Fan Motor Problems

a. Motor Overload

Over time, the fan motor can become overloaded due to dust, debris, or mechanical issues. This can cause the motor to overheat and shut down, preventing the fan from running.

b. Motor Failure

If the fan motor has failed due to age or wear and tear, it will need to be replaced to restore proper operation of the outside unit.

3. Control Board Issues

a. Faulty Relay Switch

A malfunctioning relay switch on the control board can prevent power from reaching the fan motor, causing it not to run.

b. Wiring Problems

Inspect the wiring connections leading to the fan motor. Loose, damaged, or corroded wires can disrupt the electrical flow and prevent the fan from operating.

Steps to Troubleshoot and Resolve the Issue

Step 1: Check Power Supply

Verify that the circuit breaker for your outside AC unit has not tripped. If it has, reset it and monitor if the fan starts running.

Step 2: Inspect the Capacitor

Carefully inspect the capacitor for signs of damage, such as bulging or leaking. If the capacitor appears faulty, replace it with a compatible replacement.

Step 3: Examine the Fan Motor

Attempt to manually spin the fan blades. If they move freely, check if the motor is receiving power. If the blades do not move freely, the motor may be seized and require replacement.

Step 4: Test the Control Board and Relay

Use a multimeter to test the relay switch on the control board for continuity. Replace the relay if it fails the continuity test or shows signs of damage.

Step 5: Check Wiring Connections

Inspect all wiring connections leading to the fan motor for tightness and signs of corrosion. Replace any damaged wires and ensure all connections are secure.


Dealing with an outside AC unit fan that is not running while the inside one is operational requires systematic troubleshooting to identify and resolve the underlying issues. By following the steps outlined in this guide, you can often diagnose the problem and restore proper operation to your AC system. If troubleshooting proves challenging or if components need replacement, consider seeking assistance from a qualified HVAC technician to ensure your system functions efficiently.

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