glas says 'no equipment detected' during setup and won't control my heat or ac. what do i do?

Diagnosis

The "No Equipment Detected" error on the Johnson Controls GLAS Smart Thermostat occurs when the device's onboard logic fails to identify a closed circuit or a voltage return on the expected control wires during the initial power-on self-test. Essentially, the GLAS is attempting to "ping" the R (power) wire to the other terminals (Y, W, G) to determine if you have a heat pump, conventional furnace, or multi-stage system. If the voltage doesn't return as expected, the software defaults to this error state to prevent sending power to a wire that might be improperly seated or shorted.

This failure is typically caused by one of three things: a loose connection at the terminal block, a missing C-wire (common wire) causing insufficient power for the detection relay to trigger, or a blown 3-amp or 5-amp fuse on the HVAC control board. You can confirm this by checking the voltage between the R and C wires using a multimeter; if you aren't seeing a steady 24VAC, the thermostat cannot "see" the equipment because it lacks the electrical pressure to complete the detection cycle.

How to Fix It

To resolve this, you must move from the automatic detection mode to a manual configuration to force the GLAS to recognize your hardware.

1. Power down your HVAC system at the breaker to avoid shorting the control board.
2. Remove the GLAS faceplate and inspect the wiring. Ensure each wire is stripped exactly 1/4 inch and is clamped firmly into the terminal. Tug gently on each wire; if one slides out, re-insert it and tighten the screw or press the release tab firmly.
3. Restore power to the system and wait for the "No Equipment Detected" screen to appear.
4. Navigate to the Menu button on the home screen, select Installation, and then select Equipment Detection.
5. Instead of selecting "Start Detection" again, select Manual Setup.
6. Enter your specific system configuration. For a standard single-stage gas furnace and AC, select Conventional > 1 Heat / 1 Cool > Gas/Electric.
7. Assign the terminals based on your wiring: Map the R wire to Power, W to Heat, Y to Cool, and G to Fan.
8. Save the settings and select Test Equipment. Trigger the "Heat" command; if the furnace kicks on, the detection error is bypassed and the logic is now mapped correctly.

If That Didn't Work

• Install a C-Wire Adapter: If you only have four wires (R, W, Y, G) and no C-wire, the GLAS may struggle to maintain a stable connection during detection. Install a 24V C-wire adapter (like the Add-A-Wire kit) at the furnace control board to provide a dedicated return path for power, which stabilizes the equipment sensing.
• Check the HVAC Fuse: Inspect the integrated furnace control board for a small automotive-style blade fuse (usually purple or orange). If the fuse is blown, the R-wire is dead, and the GLAS will report no equipment. Replace the fuse and restart the setup process.
• Verify Transformer Voltage: Use a multimeter to measure the voltage between the R and C wires at the thermostat wall plate. If the reading is below 22VAC, the thermostat's internal relays cannot trigger the equipment detection phase. You may need to upgrade your 24V transformer to one with a higher VA rating.
• Perform a Hard Factory Reset: If the software is hung in a detection loop, go to Menu > Settings > Reset > Factory Reset. This clears the cached "failed" detection state and allows the manual setup to take priority.

Heads Up

• Avoid "Jumpers": Never use a physical jumper wire between R and Rc on the GLAS unless specifically required by a dual-transformer system; the GLAS handles this internally via software.
• Wire Gauge: Ensure you are using 18-gauge thermostat wire. Using thinner wire over long distances can cause a voltage drop that triggers the "No Equipment" error.
• Firmware Updates: Immediately after getting the equipment recognized, connect the GLAS to Wi-Fi and check for firmware updates. Early versions of the GLAS software had known bugs regarding equipment detection on high-efficiency modulating furnaces.
• Tightness Check: Periodically check the terminal screws every six months. Thermal expansion and contraction in the wall can loosen the wires, leading to intermittent "Equipment Lost" messages.