thermostat says 'heat on' or 'cool on' but no air is coming out of my vents

Diagnosis

The Lux Kono Smart Thermostat is a "switching" device; when the screen displays "Heat On" or "Cool On," it indicates that the internal relay has closed the circuit and is successfully sending 24VAC power down the W (heat) or Y (cool) wires to your HVAC system. If the screen shows the system is active but no air is moving, the failure exists downstream from the thermostat. The "call for heat/cool" is happening, but the mechanical execution—the blower motor or the compressor—is failing to engage. This discrepancy is typically caused by a break in the electrical chain between the thermostat and the equipment, a safety trip within the furnace or air handler, or a complete power failure at the unit level. To confirm the thermostat is working correctly, you can perform a "jump test" by removing the faceplate and touching the R wire to the W or Y wire with a jumper; if the system still doesn't start, the issue is definitively with the HVAC hardware or the wiring, not the Kono interface.

How to Fix It

Follow these steps in sequence to isolate and resolve the airflow failure:

1. Check the Service Switch: Locate the toggle switch (which looks like a standard light switch) mounted on the side of your furnace or air handler. Ensure it is flipped to the "ON" position. These are frequently bumped into the "OFF" position during filter changes.
2. Inspect the Breaker Panel: Go to your main electrical panel. Look for the circuit breakers labeled "Furnace," "Air Handler," or "AC." Even if the switch looks "ON," flip it completely to "OFF" and then back to "ON" to reset any tripped internal mechanisms.
3. Verify the Condensate Overflow Switch: If you have an AC system, locate the white PVC drain line. Look for a "float switch" (a small plastic device with wires coming out of it) installed in the line. If the drain is clogged with slime, the water rises, lifts the float, and breaks the R-wire connection to prevent flooding. Vacuum out the drain line from the outside using a wet/dry vac to drop the float and restore power.
4. Furnace Flame Sensor Cleaning: If the heat is "On" but the blower never starts, the furnace may be failing to ignite. Open the lower combustion chamber, locate the flame sensor (a thin metal rod sitting in the path of the burner flame), and gently scrub it with a piece of fine steel wool or a scotch-brite pad to remove carbon buildup.
5. Outdoor Condenser Disconnect: For cooling issues, go to the outdoor unit. Open the small metal disconnect box mounted on the wall. Ensure the T-handle pull-out is firmly seated in the socket.

If That Didn't Work

• Test the Capacitor: If you hear a humming sound from the outdoor unit but the fan isn't spinning, the start/run capacitor has likely failed. This is a cylindrical silver component. If the top is bulged or leaking oil, it must be replaced with an exact match (e.g., 35/45 uF) to provide the torque needed to start the motor.
• Check the Blower Capacitor: In the indoor air handler, the blower motor has its own capacitor. If the furnace ignites (you smell gas or see heat) but the air doesn't move, the blower capacitor may be dead. Use a multimeter to test for capacitance; if it reads significantly below the rated microfarads, replace it.
• Inspect the Control Board Fuse: Most HVAC control boards have a small automotive-style fuse (usually 3A or 5A, purple or orange). If this fuse is blown, the thermostat can still "call" for air, but the board cannot distribute power to the blower or contactor. Replace the fuse and check for a short in the wiring.
• Verify C-Wire Voltage: Use a voltmeter to check for 24V AC between the R and C terminals at the thermostat. If you have low voltage (under 22V), the Kono may be able to display the screen but cannot pull enough current to keep the HVAC relay closed, causing the system to intermittently drop out.

Heads Up

• Filter Maintenance: A severely clogged pleated filter can cause the heat exchanger to overheat, triggering a "high limit switch" that shuts down the system for safety. Change your filters every 30-90 days to prevent this.
• Voltage Warning: Never touch the capacitor terminals with your bare hands, even with power off, as they store a lethal electrical charge. Discharge them using a resistor or an insulated screwdriver.
• Avoid "Rapid Cycling": Do not repeatedly flip the thermostat from Heat to Cool to "test" it. This can cause the compressor to slug liquid refrigerant back into the system, potentially destroying the valves.
• Wiring Integrity: Ensure that the wires behind the Kono are stripped exactly 3/8 of an inch. Over-stripped wires can touch and cause a short, while under-stripped wires will result in an intermittent connection that mimics a hardware failure.