Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Honeywell FC Fault — Fan Control Error
The FC fault code on Honeywell VisionPRO (8000, TH8320) and T6 Pro thermostats means a fan control error — the thermostat sent a fan signal but detected an unexpected condition in response. This code appears when the thermostat’s fan monitoring circuit doesn’t see expected feedback.
What FC Monitors
Honeywell’s communicating and zone-control-capable thermostats monitor the G (fan) terminal output. FC can trigger when:
- The thermostat sends a G signal and detects no response
- The fan output is drawing unexpected current (short)
- A communicating fan coil or AHU fails to acknowledge a fan command
Common Causes of FC Fault
| Cause | Notes |
|---|---|
| G terminal wire shorted to chassis or other terminal | Most common electrical cause |
| Failed indoor blower relay or control board | Relay coil shorted |
| Wrong wiring configuration | G wire on wrong terminal |
| Accessory (humidifier, UVCO light) wired into G | Causes excessive load |
| Thermostat firmware bug | Some early T6 Pro units had fan monitoring issues |
| Failed thermostat output circuit | Rare hardware failure |
Step-by-Step Fix
Step 1 — Check the G terminal wiring. Remove the thermostat from its base. Inspect the G terminal wire:
- The wire should not be touching the W, Y, or R terminals
- The wire insulation should be intact — no bare copper touching the base or wall plate
- Confirm it’s connected at the air handler/furnace on the G terminal (fan relay input)
Step 2 — Check fan operation at the air handler. Go to the furnace or air handler. Disconnect the G wire from the control board terminal. Briefly jump G to R (or C to G terminal if that’s the fan relay input) — the fan should come on immediately. If it does, the AHU fan circuit is fine and the problem is in the wiring or thermostat.
Step 3 — Inspect the wiring between thermostat and AHU. If there’s a zone controller, humidifier, or EAC (electronic air cleaner) inline on the G wire, disconnect them one at a time to see if the FC fault clears.
Step 4 — Factory reset the thermostat. On VisionPRO 8000: System → Equipment → Reset. On T6 Pro: hold MENU for 5 seconds, navigate to Reset. A reset clears error history and may clear a spurious FC flag.
Step 5 — Update firmware (Wi-Fi models). If the thermostat is connected to Wi-Fi, check for a firmware update through the Honeywell Home app. Some FC faults on T6 Pro were firmware bugs corrected in later releases.
When FC Appears on Non-Communicating Systems
On standard 24V wired systems (not communicating/iComfort), FC usually means a wiring problem, not a system communication issue. Focus on the G terminal wiring and relay.
Wiring Reference
| Terminal | Function |
|---|---|
| R | 24V power |
| C | Common (return) |
| G | Fan (indoor blower) |
| W / W2 | Heat stage 1 / 2 |
| Y / Y2 | Cool stage 1 / 2 |
| O/B | Reversing valve (heat pumps) |
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Replace vs. Repair
If FC persists after checking wiring and performing a factory reset, the thermostat’s output circuit has likely failed. Honeywell VisionPRO units are typically 10–15 years old at this point — replacement with a T6 Pro ($50–80) or T9 Smart ($100–140) is usually more cost-effective than chasing an internal board fault.