Fan Relay Not Working? How to Test and Replace It
When your thermostat calls for cooling but the blower fan inside your home won’t turn on, a faulty fan relay is a common culprit. The relay is a small electrical switch that tells the blower motor when to run. When it fails, air stops moving through your ducts even though the rest of the system might be running fine. The good news is that testing and replacing a fan relay is a straightforward DIY repair.
What a Fan Relay Does
The fan relay sits on or near the control board inside your air handler or furnace. When your thermostat sends a signal to turn on heating or cooling, the relay closes an electrical circuit that powers the blower motor. Some systems use a relay built into the control board, while others use a standalone relay mounted nearby. In either case, it’s essentially a switch that the thermostat controls remotely — when the relay fails, the switch stays open and the blower never gets power.
Symptoms of a Bad Fan Relay
The most obvious sign is that your blower fan won’t come on at all, even when the system is calling for air. You might hear the outdoor unit running or the furnace igniting, but no air comes through the vents. Another symptom is a blower that runs continuously and won’t shut off — this happens when the relay contacts weld together in the closed position. You might also hear a faint clicking from the air handler as the relay tries and fails to engage.
How to Test a Fan Relay
First, turn off all power to the system at the breaker. Locate the relay — it’s usually a small cube-shaped component on or near the circuit board, often labeled “FAN” on the board itself. Remove it carefully and check the coil resistance with a multimeter set to ohms. A good relay coil typically reads between 10 and 400 ohms depending on the type. An open reading (OL) means the coil is burned out. You can also test the contacts by checking continuity — with the relay de-energized, the normally open contacts should show no continuity, and the normally closed contacts should show continuity.
Replacing the Relay
Once you’ve confirmed the relay is bad, note the part number printed on the relay housing. You’ll need to match the voltage rating (usually 24V coil), the contact configuration, and the amp rating. Bring the old relay into our store and we’ll match it for you. Installation is typically as simple as pulling the old one off the board and pressing the new one into place — the pins are keyed so it only goes in one way.
When It’s Not the Relay
If the relay tests good, the issue might be the blower motor itself, the capacitor that starts the blower motor, or a wiring problem between the thermostat and the air handler. A bad control board can also mimic relay failure. If you’re not sure where the problem is, bring in whatever parts you can safely remove and we’ll test them at the counter for free.
Get the Right Relay at Open To Public HVAC Parts
We stock a wide range of fan relays, time-delay relays, and control board replacements. Bring in your old part or your model number and we’ll get you the right match. We’ve been helping Dallas homeowners with HVAC repairs since 1998, backed by 510+ Google reviews at 4.9 stars.
Open To Public HVAC Parts
10226 Plano Rd, Suite 104, Dallas, TX 75238
(214) 340-9421 — Call or Text
Monday–Friday 10AM–7PM | Saturday 10AM–3PM
