Yes, you can still install it. The thermostat includes a C-Wire Adapter for this exact situation. First, confirm you truly don't have a C-wire.
- Look at the photo you took of your old thermostat's wiring. Is the C-terminal connected? If yes, you have a C-wire.
- If the C-terminal is not connected, check the wire bundle at the wall. Pull it out gently. Sometimes an unused wire is tucked back. Look for any wire not connected to a terminal. If you find one, you can connect it as a C-wire at the furnace.
If there's no unused wire, use the included C-Wire Adapter. Do not proceed with the standard thermostat installation steps. Open the adapter's box and follow its specific guide. The adapter provides the necessary 24V power without a physical C-wire.
Heads up: If you have a zoning panel, like multiple thermostats controlling one furnace, adapter installation is more complex and you should call a professional installer.