AC Circuit Board Fuse Keeps Blowing? (What to Do)

Is the 24V DC fuse on the control board of your AC’s air handler circuit board blowing? If so then there’s definitely a short that needs to be located and fixed.

The fuse blows to protect the wiring and other components from damage that would otherwise occur when an excessive current flows as a result of the short.

This post lists the likely causes of the short and what checks you can do to locate the short and stop the fuse from blowing.

Note: This is not intended to be a detailed repair guide. It is intended to point you to the possible points of failure. Working with ACs can expose you to high voltages that can shock, and cause severe injury or even death.

Always follow proper safety precautions when conducting repairs.

What Causes the Fuse to Blow?

If the control board fuse in the air handler unit keeps blowing, it might be because (listed in order of increasing cost to repair):

#1. There is a short in the connecting wires between the air handler and the condenser. The connecting wire may have a cut or kink that’s damaged the cable causing the core inside to short and blow the fuse.

Inspect the cable for any cuts. Replace or repair the damaged section in the cabling. Replace the fuse and check if the fuse stops blowing.

#2. Contactors coils on the outside condenser coils may be burnt out causing the fuse on the control board to blow. You’ll need to replace the contactor first with a new one for the fuse to stop blowing.

#3. The circuit board on the air handler unit may be faulty and shorting causing the onboard 3A or 5A fuse to blow.

Signs the Fuse Has Blown

You may hear the DC fuse on the circuit board popping when the AC unit starts. The condenser fan may stop running as a result depending on the AC design.

Location of fuse on circuit board

The fuse is usually located on the control board of the air handler unit. It is usually a 3A or 5A automotive-type fuse.

Closing Thoughts

If the 24V fuse on the AC’s air handler circuit board keeps blowing then there’s a short. This may be on the circuit board itself, in the connecting wiring to the condenser unit outside or the contactor coil may be burnt out.

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