Lennox L40 Smart Thermostat System Diagrams

This document outlines the system wiring configurations for the Lennox L40 Smart Thermostat. It covers various HVAC system setups, including single-stage air handlers, furnaces, heat pumps, and air conditioners. The diagrams also illustrate the integration of optional components like condensate float switches and Refrigerant Detection Systems (RDS).

System Configurations

Single Stage Air Handler and Single Stage Heat Pump

This section details the wiring for a system with a single-stage air handler and a single-stage heat pump. It shows the connections to the L40 Smart Thermostat, the air handler unit (AHU), and the Lennox Typical Non-Low GWP Single Stage Heat Pump Unit. Key notes include:

Refer to the Air Handler Unit Installation Instructions for specific Lennox L40 Thermostat wiring.
An optional normally closed (NC) Condensate Float Switch can be installed.
The thermostat and outdoor unit terminal block are typically black, while the indoor unit terminal block is blue.
For heat pump applications, a Defrost Tempering Kit (67M41) must be installed.
The ACC2 terminal is factory-set for dehumidifier operation.
For heat pump applications, cut the on-board clippable link from R to O.
Install a field-provided jumper between Y2 OUT BL on the heat pump and Y2 on the indoor unit.
A Defrost Temper Kit (67M41) and Condensate Overflow Switch may be installed.

Single Stage Furnace and Single Stage Air Conditioner

This diagram illustrates the wiring for a system comprising a single-stage furnace and a single-stage air conditioner. Connections are shown for the L40 Smart Thermostat, the typical single-stage furnace, and the Lennox Typical Non-Low GWP Single Stage Air Conditioning Unit.

Single Stage Furnace and Single Stage Dual Fuel Heat Pump

This configuration covers a system with a single-stage furnace and a single-stage dual-fuel heat pump. The wiring connects the L40 Smart Thermostat to the furnace and the Lennox Typical Non-Low GWP Single Stage Heat Pump Unit. Notes for heat pump applications apply, including the installation of the Defrost Tempering Kit (67M41).

Single Stage Air Handler and Single Stage Air Conditioner

This wiring diagram is for a system utilizing a single-stage air handler and a single-stage air conditioner. It shows the connections to the L40 Smart Thermostat, the typical single-stage AHU, and the Lennox Typical Non-Low GWP Single Stage Air Conditioning Unit.

Single Stage Furnace and Single Stage Air Conditioner with Refrigerant Detection System (RDS)

This section details the wiring for a system that includes a single-stage furnace, a single-stage air conditioner, and a Refrigerant Detection System (RDS). The diagram shows the L40 Smart Thermostat, the furnace, and the optional RDS Field Kit (Cat # 27A02), including connections for RDS sensors and a condensate float switch.

Single Stage Air Handler or Single Stage Heat Pump with Refrigerant Detection System (RDS)

This wiring diagram is for systems with a single-stage air handler or heat pump, incorporating an RDS. It illustrates the connections for the L40 Smart Thermostat, the AHU/Heat Pump Unit, and the RDS Field Kit, including sensor and float switch connections.

Single Stage Furnace or Single Stage Heat Pump (Dual Fuel) with Refrigerant Detection System (RDS)

This diagram covers systems with a single-stage furnace or dual-fuel heat pump, equipped with an RDS. It shows the wiring for the L40 Smart Thermostat, the furnace/heat pump unit, and the RDS Field Kit, along with optional components like a condensate float switch.

Optional Components

Defrost Tempering Kit

The Defrost Tempering Kit (67M41) is required for heat pump applications to ensure proper operation in defrost cycles.

Condensate Float Switch

An optional normally closed (NC) Condensate Float Switch can be installed to detect and prevent water overflow from the condensate drain pan.

Refrigerant Detection System (RDS)

The RDS Field Kit (Cat # 27A02) is an optional component that detects refrigerant leaks. It connects to the thermostat and the HVAC system, with provisions for sensors and alerts.

	Lennox ML13KC1 Merit Series Air Conditioner Specifications Detailed product specifications for the Lennox ML13KC1 Merit Series single-stage air conditioner, including features, technical data, dimensions, and installation guidelines.
	Lennox ML14KP1 Merit Series Heat Pump Product Specifications Comprehensive product specifications for the Lennox ML14KP1 Merit Series residential heat pump. This document details features, performance data, electrical specifications, dimensions, and installation requirements for models ranging from 1.5 to 5 tons, utilizing R-454B refrigerant.
	Lennox EL15KC1 Elite Series Air Conditioner Product Specifications Detailed product specifications for the Lennox EL15KC1 Elite Series single-stage air conditioner, including features, applications, refrigeration system details, compressor information, controls, and technical data.
	Lennox EL297UHE(K) Elite Series Gas Furnace Specifications Detailed specifications and features for the Lennox EL297UHE(K) Elite Series residential gas furnace, highlighting its 97% AFUE, two-stage heating, constant torque blower, and advanced controls for optimal home comfort and energy efficiency.
	Lennox EL297UHV(K) Elite Series Gas Furnace: High-Efficiency Residential Heating Discover the Lennox EL297UHV(K) Elite Series gas furnace, engineered for exceptional residential comfort and efficiency. Featuring 97% AFUE, a variable speed blower, and advanced controls, this furnace provides reliable, quiet, and cost-effective heating. Explore its specifications and features for optimal home climate control.
	Lennox EL297DFE(K) Elite Series Gas Furnace Product Specifications Detailed product specifications for the Lennox EL297DFE(K) Elite Series residential gas furnace, highlighting its 97% AFUE, two-stage heating, and advanced features for efficient home comfort.
	Lennox EL297DFE(K) Elite Series Gas Furnace Product Specifications Detailed product specifications for the Lennox EL297DFE(K) Elite Series Gas Furnace, including features, applications, installation, and performance data. This two-stage, constant torque blower furnace offers up to 97% AFUE and is designed for residential use.
	Lennox Merit Series: Achieve Perfect Air for Your Home Discover the Lennox Merit Series, offering efficient, reliable, and comfortable whole-home HVAC solutions. Learn about furnaces, air conditioners, heat pumps, and smart thermostats designed for perfect air quality and energy savings.