Lennox Furnace Repair

The thermostat when NOT in configuration mode has detected an unknown device. Typically the thermostat will send a command to the unknown device and place the device into a soft disable state. The soft disable control will indicate so as follows:
– On air handler, furnace and outdoor controls, the soft-disabled state is displayed by double horizontal lines on seven-segment display.
– On the damper control module, the green LED will flash 3 seconds on and 1 second off.
– On the equipment interface module, the green LED will flash 3 seconds on and 1 second off.
– A new communicating device has been added to the system since the original configuration setup was completed.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating devices attached.

The thermostat cannot find a previously installed system component.
– Check all system components (devices) connections to make sure they are Lennox communicating compatible.
– Cycle system power.
– If problem persists, then check all system components (devices) connections to make sure they are Lennox communicating compatible.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating components attached.

Thermostat did not find an indoor unit. Make sure there is an Lennox communicating indoor unit on the system.
– Check for voltage and missing component.
– Check R, i+, i- and C connections.
– Ohm wires for electrical continuity.
– Cycle power to both indoor unit first and then thermostat.
– Verify that equipment interface module (if applicable) is configured as either an air handler or furnace when used with a non-communicating indoor unit.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating components attached.
– Replace indoor unit control if there is no response.

Thermostat found more than one outdoor unit, or more than one indoor unit, or more than one thermostat connected to the system.
– Thermostat will display the message Too Many Devices of the Same Type.
– Check wiring and remove duplicate equipment.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating components attached.

The thermostat found more than one thermostat, indoor or outdoor unit on the system.
– Check wiring and remove duplicate equipment.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating components attached.

Incorrect parameter settings detected. Dealer would need to re-set the system and start configuration again.

The iComfort thermostat cannot work with one of the devices because the thermostats firmware needs to be updated first

Equipment is trying to be utilized that is not compatible with other system components, such as a single-stage non-variable speed motor furnace with a modulating outdoor unit.

code 29 will lock out cooling and heating and not allow the system to cool down the home. If you have a code 29 you should run the system in installer test mode. This will bypass the lock out condition but still have other safeties protecting the system. Tstat shows ‘– –’ when indoor temperature goes above 99. The test mode continues cooling even when alert #29 is present enabling the system to cool the home. The test mode stops cooling if there are mechanical safety alerts such as pressure trips. Technician is expected to be on-site for this test.

The thermostat will not allow any cooling operation to begin until it senses a temperature higher than 40ºF.
– Cooling operation is not allowed.
– Check to ensure that cooling equipment is not stuck ON.
– Check accuracy of the thermostat temperature sensor.
– Select heating system mode to heat the indoor space to above 40ºF.

The applicable system component (indoor, equipment interface, damper control module or outdoor unit) has not communicated with thermostat for more than three minutes.
– Check connections and voltages.
– Ohm wires for electrical continuity.
– If float switch is installed on air handler drain pain, check condensate line to ensure it is not clogged and tripping the float switch connected in series with R terminal.
– Check to see if freezestat is installed.

The applicable system component (device) is resetting itself. This issue may occur during a power outage or power fluctuation in the system. If persistent or if it coincides with the system operations then proceed with the following troubleshooting steps.
– Check the power connections.
– Check the amperage draw at the transformer (possible overloaded).
– Check 24VAC voltage at the system component (device).
– If the fault persists after checking the connections, replace the applicable control.

The thermostat does not know the capacity (tonnage) of the indoor or outdoor unit. The applicable system component is missing the programmed unit capacity.
– Remove power to thermostat before programming the unit control.
– Go to applicable unit control and program the unit capacity manually (see the unit installation instruction for configuration instructions).
– Once configuration is complete then reconnect thermostat wires.
– Go to menu > settings > advanced settings > view dealer control center > equipment and press reset all equipment. This will allow the system to auto-detect any Lennox communicating components attached.

Message sent by thermostat to unit after more than 15 minutes asking for initiating heating or cooling with no response from unit.
Message sent by thermostat to unit after more than 15 minutes asking for termination of heating or cooling with no response from unit.
– Communicating system: Wire a transient voltage suppressor in parallel with the compressor contactor coil terminals on the outdoor unit.
– Non-communicating outdoor unit: Wire transient voltage suppressor (89W72) in parallel with compressor contactor coil or across the Y1 and C terminals on the indoor control board.
– See service and application note IAQ-10-01 for further details.
– Transient Voltage Suppressor Part information: Made by Little Fuse, part number 5KP43CA bidirectional Transorb aka TVS Diode. Please contact your FTC or inside technical support for help in acquiring the transient voltage suppressor if not available in your local electronics store.

The system has been heating for at least 15 minutes without a demand for heating.
– Run the system in diagnostic mode and verify that it matches actual equipment operation. Go to menu > settings > advanced settings > dealer control center > diagnostics and press the start diagnostics button.
– Check for other alert codes that may be preventing the system from operating as expected.
– Check all heating equipment to determine cause of heating demand.
Recycle power.

The system has been cooling for at least 15 minutes, without a demand for cooling.
– Run the system in diagnostic mode and verify that it matches actual equipment operation. Go to menu > settings > advanced settings > dealer control center > diagnostics and press the start diagnostics button.
– Check for other alert codes that may be preventing the system from operating as expected.
– Check all cooling equipment to determine cause of cooling demand.
Recycle power.

The system has not been able to turn on the heating for more than 45 minutes.
– The system will go off-line for 60 minutes and will attempt to restart itself.
– Run the system in diagnostic mode and verify that it matches actual equipment operation. Go to menu > settings > advanced settings > dealer control center > diagnostics and press the start diagnostics button
– Check for other alert codes that may be preventing the system from operating as expected.
– Check all heating equipment to determine cause.
– Recycle power.

This alert code will appear anytime a communicating control [Furnace, air handler, PureAir S, damper control module, air conditioner or heat pump] is replaced in the system.

One of the system components has lost communication with the system. The system component (device) is unable to communicate.
– S30 – Access dealer control center, select notifications icon, review alert code details to determine which device or unit has the communication problem. Review both active and cleared alerts.
– Wi-Fi – Press and hold the Lennox logo on the bottom right of stat for 5 seconds to access the dealer control center. Follow the prompts to access the dealer / installer screen and select the Alerts tab. Review alert code details to determine which device or unit has the communication problem. Review both active and cleared alerts.
– Zoning – Remove wire from smart hub to iHarmony control and just have wiring from furnace.
Troubleshooting:
– Check each control for additional codes
– In most cases issues are related to electrical noise. Verify that high voltage power is separated from the low voltage communication wires.
– Check for proper grounding on line voltage and low voltage wiring, transformer and equipment.
– Check for incorrectly wired or loose or spliced connections between system components (devices or units).
– Make sure all unused wires are tied together and taken back to the C terminal on the indoor control board as shown in the installation and setup guide.
– Make sure that smart hub has proper software version for added accessory. (Example: Pure Air S and/or Apple Home Kit must have software version 3.4 or higher before it will connect to system properly. (If software is not updated in system it will cause system operation issues).
– If zoning is installed and is wired directly from smart hub to iHarmony control then disconnect that wiring. Run control wiring from the iHarmony control directly to the indoor unit control. Wiring diagrams are provided in the iHarmony Installation and Setup Guide.
– When using a float switch, use isolation relay to break common wire to outdoor unit. For testing purposes, remove float switch from the circuit.
– Disconnect all wiring to other system components (except thermostat to indoor unit) and reconnect one device at a time and recommission system each time a device is reconnected until the issue is located.
– Automatically clears when the system detects the issue no longer exists.

The component AC line voltage is too low. This alert code may appear during a brownout.
– It may also occur when line voltage is below its designed operating value.
– Check and correct the power line voltage.

The unit is reporting that its power and neutral lines are reversed.
– Turn off the power to the system and correct the line power voltage wiring.
– System resumes normal operation five seconds after critical condition is recovered.

The reporting component cannot find earth ground. The thermostat will shut down the system.
– Provide proper earth ground to the equipment.
– System resumes normal operation five seconds after critical condition is recovered.

Line voltage high (voltage higher than nameplate rating).
– Provide power voltage within proper range.
– System resumes normal operation five seconds after critical condition is recovered.

24VAC power to a system component control is lower than the required range of 18 to 30VAC.
– Check and correct voltage.
– Check for additional power-robbing system components (devices) connected to system.
– This alert code may require the installation of an additional or larger VA transformer.
– Damper control module will operate in non-zone mode until proper voltage is restored.

Thermostat will display this code when 24VAC power is high (18 to 30 VAC).
– Will display Furnace or Air Handler High Secondary (24VAC) voltage.

The reporting unit has poor earth grounding.
– Provide proper grounding for the system component (device).
– Check for proper earth ground to the system.
– Reference Service and Application Note H-01-09 for additional information.

There is a delay in the system component responding to the system. Typically this alert code does not cause any operational issues and will clear on its own.
– This alert code is usually caused by a delay in the outdoor unit responding to the thermostat.
– Check all wiring connections.
– See Service and Application Note H-01-09 for additional information.

The thermostat has lost communication with a system component for more than three minutes. System component has lost communication with the thermostat. See 4. Electrical Troubleshooting on page 60 for assistance.
– Check the wiring connections between components.
– Ohm wires.
– Cycle power.
– Any component that is miss-wired may cause a false component code to be shown on system component.
– Disconnect all wiring to other system components and check communication one at a time.
– When using a float switch, use isolation relay to break common wire to outdoor unit. For testing purposes, remove float switch from the circuit
– This alert code stops all associated system operations and waits for a heartbeat message from the system component that is not communicating.

There is a hardware problem on a system component control. There is a control hardware problem.
– Replace the control if the problem prevents operation and is persistent.
– Damper control module will remain in non-zone mode (all dampers open) for five minutes after priority condition no longer exist.
– Remove jumper if present on indoor unit between R and W2 if equipment interface module is in use.
– On the PureAir S control the jumper selector is missing.

There is an internal hardware problem on the system component control. In addition, if you have zoning the alert code is triggered when your zone temperature is deviating away from set point persistently.
– Typically the system component control will reset itself.
– Replace the system component (device) control if the problem prevents operation and is persistent.

Configuration jumper missing on equipment interface module.
– Install the missing jumper.
– Set as heat pump, furnace control or air handler control.
– This is applicable in non-communicating applications only).

System component control software is corrupted.
– Recycle power.
– If failure re-occurs, replace the system component control.

The thermostat has found a problem with the outdoor temperature sensor. In normal operation after system component control recognizes sensors, the alert code will be sent if valid temperature reading is lost.
– Compare outdoor sensor resistance to temperature / resistance charts in unit installation instructions.
– Replace sensors pack if necessary.
– At the beginning of (any) configuration, furnace, air-handler control or equipment interface module will detect the presence of the sensor(s).
– If detected (reading in range), appropriate feature will be set as ‘installed’ and shown in the ‘About’ screen.

The furnace roll out limit switch is open. Correct the cause of roll out trip.
– Reset roll out switch.
– Test the furnace operation.
– Check for blocked or obstructed vent pipe (Intake and/or Exhaust).
– Check for flame stability, if flame is unstable, look for cause.

Lost communication with indoor blower motor.
– Possible causes include power outage, brown-out, motor not powered, loose wiring, condensation on system component control without cover on breaker.
– Problem may be on system component control or motor side.

The unit size code for the indoor unit and the size of blower motor do not match. Incorrect appliance unit size code selected.
– Remove the thermostat from the system while applying power and reprogramming.
– Check for proper configuring under unit size codes for furnace/air handler in configuration guide or in installation instructions.

The unit size code for the indoor unit has not been selected or set incorrectly.
– Verify that the correct unit size code is configured. Unit size codes for furnace and air handler are listed in the system component configuration guide or installation instruction.
– Remove the thermostat from the system while applying power and set the unit size code per instructions provided in the indoor unit installation instruction.

There is an issue with the furnace gas valve.
– Check gas valve operation and wiring.
– Check for voltage to the gas valve.

The furnace gas valve relay contact is closed. Verify wiring on control and gas valve or in good order, not missing or damage.

The furnace gas valve second-stage relay is faulty.
– Furnace will operate on first-stage for the remainder of the heating demand
– If unable to operate second-stage, replace furnace control.

The furnace hot surface igniter is open.
– Measure the resistance of hot surface igniter.
– Replace the igniter if it is not within the specified range found in furnace installation instruction.

The furnace low pressure switch is open.
– Check pressure (inches w.c.) of the low pressure switch closing during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockages and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold end heater box.
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace low pressure switch is stuck closed.
– Check operation of low pressure switch to see if it is stuck closed for longer than 150 seconds during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockage and combustion air inducer for correct operation and restriction.
– Check for moisture in pressure switch.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.
– Other possible issues that are specific to the iComfort Wi-Fi are as follows:
– It has been determined that this alert code is generated when a subsequent heating call occurs within 30 seconds of a prior call for heat ending. If a call for heat occurs during this time period, the inducer post-purge from the previous call may still be in process. If that condition exists, the IFC will sense the pressure switch circuit is closed therefore activating the alert code 224 and generate an email notification. Once the fault is cleared, typically seconds after being generated, the subsequent call for heat will be initiated and the furnace will return to normal operation.
– Lennox has not received any complaints of no heat situations associated with this operating condition. It has been determined that occasionally the fault clears itself and the alert code is not stored in the IFC or iComfort Wi-Fi™ thermostat.

The furnace high pressure switch will not close.
– Check pressure (inches w.c.) of high pressure switch closing during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockage and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box or condensate drain or drain strainers at outlet of the cold end heater box.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace high pressure switch will not open.
– Check operation of high pressure switch closing during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockage and combustion air inducer for correct operation and restriction.
– Check for moisture in pressure switch.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace low pressure switch is open while in run mode.
– Check pressure (inches w.c.) of low pressure switch closing during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockage and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold end heater box.
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace failed to successfully perform the heating system calibration.
– This calibration routine calibrates the speed (RPM) of the Combustion Air Inducer Assembly to the specific static pressure (air flow resistance) of the unique venting system application. 
– Calibration varies the combustion air inducer speed to close and re-open the low and high pressure switches during the routine to ensure sufficient primary/secondary air to support combustion at all firing rates from lowest to highest.
– A dual-port manometer is required to diagnose the system calibration and pressure switches. The 10L34 kit includes all the hoses and fittings needed to test the system pressure.
– Inspect vent for blockage and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold end heater box (CEHB).
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace Pressure Switch Troubleshooting” for additional information. (Check all of the above before replacing the pressure switch)

Furnace control switched to high fire ignition because low fire pressure switch did not close in allowed time.
*Early models only, if fan is on when call for W1 is initiated unit will fire on high fire for 60 seconds before dropping down to low fire.

The furnace flame current is low.
– Check micro-amperes of the flame sensor using thermostat or control board.
– Clean or replace the flame sensor.
– Measure voltage of neutral to ground to ensure good unit ground.
– Clean face of burner assembly.
– Refer to Service and Application Note H-14-06 Flame Rectification In All Gas Furnaces for additional information.

Flame sensed without call for gas heating. Perform the following:
– Shut off gas.
– Check for a gas valve leak.
– Check for voltage to gas valve.
– Replace the gas valve if needed.

The furnace primary limit switch is open. If limit switch is not closed within three minutes, the unit will go into a 60 minute soft lockout (Watchguard mode). Perform the following:
– Check for high gas pressure.
– Check for low supply air. Low supply air due to being plugged or restriction in system (example: dirty air filter or blockage in duct work).
– Check for proper firing rate on furnace.
– Check for non-functioning zone dampers.
– Limit trips will place the iHarmony zoning system into non-zone mode.
– See ACC-14-01 for further details.

A discharge air-temperature is high. Perform the following:
– Check temperature rise, air flow and input rate.
– Check for dirty air filter(s).
– See Service and Application Note ACC-14-01 for further details.

The furnace is in Watchguard mode. The furnace igniter cannot turn on the flame. This is a five strike condition during a single demand.
– Check for proper gas flow.
– Ensure that igniter is lighting burner.
– Check flame sensor current.
– Check for dirty filters.
– Check for blocked cold end heater box or condensate drain and cracked hoses.

The furnace is in Watchguard mode. The furnace low pressure switch is open. This is a five strike condition during a single demand.
– Check pressure (inches w.c.) of low pressure switch closing during a heat call.
– Measure operating pressure (inches w.c.).
– Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet of CEHB and cracked hoses.
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace low pressure switch is open during run mode. The system will go into Watchguard mode.
– Check operation of low pressure switch to see if it is stuck open during a heat call.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockages, and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet of CEHB and cracked hoses.
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

The furnace flame is going off during a heating cycle. The system will go into Watchguard mode.
– Check micro-amperes of flame sensor using thermostat diagnostics.
– Clean or replace sensor.
– Measure voltage of neutral to ground to ensure good unit ground.
– Clean face of burner assembly.

The furnace limit switch has been open for more than three minutes. The system will go into Watchguard mode.
– Check firing rate and air flow.
– Check for air blockage.

The furnace flame is out of sequence. The system will go into Watchguard mode.
– Shut off gas.
– Check for gas valve leak.
– Check for high gas pressure.
– Low supply air due to being plugged or restriction in system (example: dirty air filter or blockage in duct work).
– Limit trips will place the iHarmony® zoning system into non-zone mode.
– Check for proper firing rate on furnace.
– Check for non-functioning zone dampers.
– Refer to Service and Application Note ACC-14-01 – iHarmony® and SLP98 – Insufficient Zone Heating and Alert Code 250 Issues for corrective actions.

The furnace is not able to calibrate or the high pressure switch opened or failed to close in run mode. The system will go into Watchguard mode.
– Measure operating pressure (inches w.c.).
– Inspect vent for blockages, and combustion air inducer for correct operation and restriction.
– Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet of CEHB and cracked hoses.
– Check for cracked hoses.
– Check levelness of unit.
– Check Service Manual and Service and Application Note H-13-07 Condensing Furnace Pressure Switch Troubleshooting for additional information.

There is a problem with the furnace ignition circuit. The system will go into Watchguard mode.
– Measure resistance of hot surface igniter.
– Replace the hot surface igniter; it is not within specifications.
– Measure voltage to igniter.

The heating airflow is below the minimum required level. The system will go into Watchguard mode.
– Check for dirty air filter(s) and other air flow restrictions.
– Check blower performance.

The indoor unit blower motor will not start. The system will go into Watchguard mode.
– Indoor blower motor unable to start.
– This could be due to seized bearing, stuck wheel, and obstructions.
– Replace motor, motor module or wheel if assembly does not operate or meet performance standards.

There is over current in the furnace inducer motor. The system will go into Watchguard mode.
– Check combustion blower bearings, wiring and amps.
– Replace furnace inducer motor if it does not operate or does not meet performance standards.
– Refer to Service and Application Note H-17-02 All Communicating Variable Speed Motors.

The indoor blower motor is overheating. Indoor blower motor over temperature (motor tripped on internal protector).
– Check motor bearings and amps.
– Replace indoor blower motor if necessary.
– Check for high duct static.

There is a discharge air temperature sensor issue.
– Compare discharge temperature sensor (DATS) resistance to temperature / resistance charts in system component installation instruction.
– Replace discharge air sensor if necessary.
– Confirm there is no short or open circuits in the Lennox communicating thermostat connections to any of the other components in the communication system.
– Issues with a DATS connected to a damper control module or equipment interface model will not generate an alert code.

The heat firing rate has been reduced to match available airflow (cutback mode). This is a warning only alert code.
– Furnace blower in cutback mode due to restricted airflow.
– Reduce firing rate every 60 seconds to match available CFM.
– Check air filter and duct system.
– To clear, replace air filter if needed or repair or add additional ducting.
– Two-stage controls will reduce firing rate to first stage.

The indoor blower cannot provide the requested CFM due to excessive static pressure. This is a warning only alert code.
– Static pressure has exceeded the capability of the blower motor.
– Possible restricted airflow – Indoor blower is running at a reduced CFM (Cutback Mode).
– The variable speed motor has pre-set speed and torque limiters to protect the motor from damage caused by operating outside of design parameters (0 to 0.8” e.g. total external static pressure).
– Check air filter and duct system.
– To clear, replace air filter if needed or repair or add additional ducting.

Link Relay Problem. Relay Y1 Failure which will result in the all system operations stopping.
– Relay is located on the IFC (Integrated Furnace Control). If issue continues replace IFC.

Sequence of Operation: Communicating room thermostat send a Y1 or Y2 cooling or heat pump demand to the indoor control asking it to send a Y1 or Y2 output to the outdoor unit, right? The indoor control then looks to see if it sees 24 volts between the Y1 and common or Y2 and common on its terminals. If it does not see 24 volts, it sets the code 347.
– The Y1 relay on the applicable system component has failed. Either the pilot relay contacts did not close or the relay coil did not energize.
– System operation will stop.
– Possible Y1 relay / stage 1 failure.
– Pilot relay contacts did not close or the relay coil did not energize;
– There is no input back to the applicable system component control.

Sequence of Operation: Communicating room thermostat send a Y1 or Y2 cooling or heat pump demand to the indoor control asking it to send a Y1 or Y2 output to the outdoor unit, right? The indoor control then looks to see if it sees 24 volts between the Y1 and common or Y2 and common on its terminals. If it does not see 24 volts, it sets the Alert Code 348.
– The Y2 relay on the applicable system component has failed. Either the pilot relay contacts did not close or the relay coil did not energize.
– Possible Y2 relay / stage 2 failure.
– Furnace pilot relay contacts did not close or the relay coil did not energize
– No input back to furnace or air handler control.

The O to R link on the furnace needs to be restored.
– Configuration link R to O needs to be restored.
– Repair cut link by hard-wiring the R to O terminals on the terminal strip.
– Only applicable in non-communicating mode.
– Possible cause brown out. Might result in low voltage to which would generate alert code.

Communicating Mode:
– In communicating mode, the DS terminal will be used to monitor a field-installed interlock switch. When operating in this capacity, the DS jumper will be monitored as follows:
– The on-board jumper DS-R (W914) will be cut.
– When no alert codes are present there will be 24VAC present at this terminal.
– When controls see the loss of 24VAC for 2 minutes it will send an alert code 370 and disable all service bits.
– If currently running a demand, de-energize all outputs (including the blower).
– The alert code will clear when 24VAC is continuously sensed on DS terminal for a minimum of 10 seconds and the respective alert code clearing message will be sent and service bits restored.
In case of an existing interlock switch alert code, upon power reset, an alert code message shall be sent if voltage is not sensed on the DS terminal. An alert code clearing message will be sent if 24VAC is sensed on DS terminal for the minimum of 10 seconds.
– The monitoring of DS terminal will apply to both variable speed and constant torque controls.
Non-Communicating Mode:
– The furnace control has not received 24VAC power for two minutes or more on the DS terminal
– The system will not operate.
– Dealer has cut the W914 jumper (Dehum, Harmony III) on the Lennox furnace control.
– The thermostat monitors the DS terminal in the furnace for power and if the link has been cut then power will be lost to DS.

Interlock relay failure (furnace or air handler modes only).
– Interlock relay is energized, but input is not sensed after three seconds.
– There will be no heating or cooling due to this alert code – moderate condition.
– De-energize interlock relay and energize after five minutes if demand is still present – critical condition.

Interlock relay stuck (furnace or air handler modes only).
– Interlock relay continuously sensed (with relay off).
– There is no heating and cooling operation – moderation condition.
– After 10 minutes if event still exist it will be escalated to priority condition critical.

Relay W1 failure (furnace or air handler modes only). W1 relay is energized but input is not sensed after three seconds.