Johnson Controls
Relay Chatter / Coil Noise
Thermostat emits a buzzing or clicking noise when switching modes or calling for heat/cool.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Low or unstable 24 VAC supply, Failing relay on thermostat PCB, Electrical noise from nearby high‑voltage lines, Loose thermostat mounting causing vibration
How to Fix / Troubleshooting
Safety: Turn off power to HVAC equipment before removing the thermostat.
- Step 1 – Check mounting: Ensure the thermostat is firmly attached to the sub‑base and the sub‑base is securely mounted to the wall.
- Step 2 – Inspect wiring path: Avoid running thermostat cable parallel and close to high‑voltage lines. If they share a conduit, consider rerouting.
- Step 3 – Measure voltage: Verify that 24 VAC between R and C is stable and within range. Low voltage can cause relay chatter.
- Step 4 – Replace thermostat: If voltage is stable and noise clearly comes from internal relays, replace the thermostat main control board or entire thermostat.
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Repair Difficulty
Medium
3/5
Required Part
Main Control Board (Relays)
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