SERVICE CALL: Upon arrival homeowner stated the Ac is not Working at all. After complete troubleshooting I found the Duel Fuel unit Lennox 4 Ton capacity 5 years old communicating system Is not working at all due to Main smart thermostat s 30 Lennox was Removed from the system and somebody install regular thermostat Which is not compatible with this type of High efficiency system. I recommend to install new S 40 thermostat and then test complete System to make sure is working properly plus recommend routine Maintenance on complete system. Homeowner accepted Quote for New smart thermostat we will place the order and return asap to Complete repairs. Thanks for choosing TE CERTIFIED.