Lennox system shows E450 condensate overflow or float switch error; cooling is disabled even though thermostat is calling.

Safety: Turn off power to the indoor unit. Water around electrical components is hazardous.

• 1. Inspect drain pan: Remove the blower/coil access panel and check the primary and secondary drain pans for standing water. Use a wet/dry vacuum to remove water if present.
• 2. Clear condensate drain line: At the outside termination or cleanout, use a wet/dry vacuum to suck out debris and algae. Flush the line with a mixture of water and a small amount of vinegar or approved condensate cleaner.
• 3. Check float switch: Locate the float switch on the pan or drain line. Manually lift and release the float to ensure it moves freely and clicks. Replace if stuck or corroded.
• 4. Verify trap and slope: Ensure the drain line has a proper trap (for negative pressure systems) and slopes continuously downward to the outlet.

Note: Do not bypass the float switch; it protects your home from water damage.