Error Code Y Signal Without G Signal

York TM9V080B12MP11 Error Code Y Signal Without G Signal: Y Signal Without G Signal

TL;DR
Your York furnace is receiving a cooling signal (Y) without a blower signal (G) from the thermostat — a wiring issue. Check the thermostat wiring connections and replace the thermostat batteries if applicable.
Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code Y Signal Without G Signal Mean?

The 4-amber-flash code on the York S1-33103010000 board means the control board is receiving a signal on the Y (cooling) terminal from the thermostat without a corresponding signal on the G (fan/blower) terminal. In a properly wired system, when the thermostat calls for cooling, both Y and G should be energized so the blower runs while the AC compressor operates.

This is a thermostat wiring configuration issue, not a furnace malfunction. The most common cause is a missing or loose G wire connection at either the thermostat or the furnace terminal strip. This can happen after a thermostat replacement if the installer forgot to connect the G wire, or if a wire has vibrated loose over time.

While this code relates to cooling rather than heating, it indicates that your HVAC system will not operate correctly in cooling mode — the blower will not run when the air conditioner cycles on, which can cause the evaporator coil to freeze. It is worth addressing even during heating season to ensure your system is ready for summer.

How to Fix It: Check Thermostat Wiring and Batteries

âš  Safety First
Always turn off the furnace at the power switch or breaker and shut off the gas supply before beginning. Do not proceed if you smell gas — leave the area and call your gas company immediately.

What You'll Need

Steps

  1. Turn off power AND shut off gas supply Turn the furnace power switch OFF. Turn the gas shutoff valve to OFF (perpendicular to pipe). If you smell gas at any point, leave the area immediately and call your gas company.
  2. Check thermostat batteries If your thermostat uses batteries, replace them with fresh ones. Low batteries can cause erratic signals and incomplete communication with the furnace control board.
  3. Inspect thermostat wiring at the thermostat Remove the thermostat from its wall plate (most pull straight off or have a release tab). Look at the wiring terminal strip on the wall plate. Verify that a wire is connected to the G terminal. If the G terminal is empty, you may have a spare wire in the cable bundle that can be connected. If a wire is present but loose, push it firmly into the terminal.
  4. Inspect wiring at the furnace terminal strip At the furnace, find the low-voltage terminal strip (usually on or near the control board). Verify that the G wire is connected and secured. Match the wire color at the furnace end to the wire color at the thermostat end for the G terminal.
  5. Restore power and test Turn gas back ON. Restore furnace power. Set the thermostat to cooling mode and lower the set temperature below room temperature. Verify that both the compressor (outdoor unit) and the blower (indoor fan) start.
How to Verify
After correcting the wiring, the 4-amber-flash code should clear. The LED should show slow green flash (standby) when no call for heat or cooling is active. If you switch to cooling mode, the blower should run while the AC operates. If the code persists, there may be a broken wire inside the thermostat cable wall, which requires professional rewiring.

When to Call a Professional

Contact a licensed HVAC technician if:

Sources

  1. Johnson Controls S1-33103010000 Installation Manual (ManualsLib)