Honeywell Home
Thermostat Relay Operating but No 24VAC Output to Equipment
Thermostat clicks but furnace or AC does not start
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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
Broken thermostat internal relay contacts, Loose R, W, or Y connections, Open safety switch in equipment, Blown low‑voltage fuse
How to Fix / Troubleshooting
Safety: Turn off power to HVAC equipment before handling wiring. Use a multimeter only if you are comfortable with electrical testing.
- Check thermostat wiring: Ensure all wires are fully inserted and clamped at the thermostat wall plate.
- Inspect furnace/air handler board: Look for a blown low‑voltage fuse and replace if necessary after checking for shorts.
- Test for 24VAC at call terminals: With a call for heat or cool active, measure between R and W (heat) or R and Y (cool) at the furnace board. If no voltage is present, the thermostat or wiring is faulty.
- Bypass thermostat (advanced): Temporarily jumper R to W or Y at the furnace board. If the system starts, replace the thermostat or repair the thermostat cable.
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Repair Difficulty
Hard
4/5
Required Part
Honeywell Home Smart Thermostat Main Assembly
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