Choose Product
Identify Problem
03
Find Solutions
HomeRepair HelpLennox Central A/C RepairLennox Central air conditioner won't turn off Repair

Lennox Central air conditioner won't turn off

If your Lennox central air conditioner won't turn off, a shorted contactor or a bad wall thermostat or thermostat wiring is the most likely cause, keeping a cooling signal on the yellow (Y) terminal even after the thermostat is set to Off. A shorted furnace control board or main control board can cause the same problem, though it is a less common cause, by continuing to send voltage to the outdoor condensing unit and making the air conditioner run constantly. A shorted control board or main control board can continuously send voltage to the outdoor condensing unit, making the air conditioner run constantly even when the thermostat is set to off. Next, check the wall thermostat or thermostat wiring. A stuck electrical contact between the common "C" and yellow "Y" thermostat wire terminals can keep signaling the contactor to run. A failed contactor is less common, but a shorted contactor can also provide continuous power to the condenser components. This central air won't turn off problem may be caused by a control board, thermostat, thermostat wire issue, or contactor. Enter your Lennox model number to find the exact replacement part for your specific central air conditioner. You can inspect the thermostat and control board for visible damage, but testing continuity and working around the contactor, condensing unit, or other 240-volt line-voltage components requires power to be disconnected and should be handled by a qualified HVAC technician if you are not trained to do so. No refrigerant handling is needed for these repairs.

01 - Lennox Central Air Conditioner Control Board

If the furnace control board has a short, it may be providing continuous voltage to the central air condensing unit preventing it from turning off. Inspect the control board for any damage and replace if necessary.
Enter model number to search for the required part specific to your product
Need help finding your model number?
Shop all Lennox Central Air Conditioner Control Board Parts
Common

02 - Lennox Central Air Conditioner Main Control Board

If the furnace's main control board has a short, it may be providing continuous voltage to the central air condensing unit preventing it from turning off. Inspect the control board for any damage and replace if necessary.
Shop all Lennox Central Air Conditioner Main Control Board Parts
Common

03 - Lennox Central Air Conditioner Wall Thermostat

The wall thermostat has electrical contacts that send signal voltage back to the control board and the condensing unit's contactor to run the central air system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the central air system to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the wall thermostat shows continuity between the common (“C”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the off position, the thermostat has failed and will need to be replaced.
Shop all Lennox Central Air Conditioner Wall Thermostat Parts
Common

04 - Lennox Central Air Conditioner Wifi Thermostat

The WiFi thermostat has electrical contacts that send signal voltage back to the control board and the condensing unit's contactor to run the central air system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the central air system to run continuously. To determine if the thermostat is defective, use a multi-meter to test it for continuity. If the WiFi thermostat shows continuity between the common (“C”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the off position, the thermostat has failed and will need to be replaced.
Shop all Lennox Central Air Conditioner Wifi Thermostat Parts
Common

05 - Lennox Central Air Conditioner Contactor

The furnace control board sends a low voltage signal to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the condensing unit components. If the contactor has shorted, it can send continuous voltage to the condensing unit's components resulting in the central air system not turning off. To determine if the contactor is at fault, use a multimeter to test the contactor for a short. If the contactor has shorted, replace it.
Shop all Lennox Central Air Conditioner Contactor Parts
Less Common

Frequently Asked Questions

Why won't my Lennox central air conditioner turn off?
How do I know if my AC thermostat is causing the air conditioner to run constantly?
Can a bad condenser contactor make my AC unit keep running?
Should I replace the Lennox control board if my air conditioner will not shut off?
How do I find the correct Lennox thermostat, contactor, or control board replacement part?

Shop by Lennox Central Air Conditioner Parts

Lennox Central Air Conditioner Axle, Roller, Shaft, Wheel Replacement Parts
Lennox Central Air Conditioner Bearing Replacement Parts
Lennox Central Air Conditioner Belt Replacement Parts
Lennox Central Air Conditioner Blade Replacement Parts
Lennox Central Air Conditioner Blower Wheel & Fan Blade Replacement Parts
Lennox Central Air Conditioner Bracket & Flange Replacement Parts
Lennox Central Air Conditioner Cap, Lid & Cover Replacement Parts
Lennox Central Air Conditioner Capacitor Replacement Parts
Lennox Central Air Conditioner Circuit Board & Timer Replacement Parts
Lennox Central Air Conditioner Cleaner & Deodorizer Replacement Parts
Lennox Central Air Conditioner Compressor & Sealed System Replacement Parts
Lennox Central Air Conditioner Diode, Magnetron & Resistor Replacement Parts
Lennox Central Air Conditioner Dispenser Replacement Parts
Lennox Central Air Conditioner Drawer Replacement Parts
Lennox Central Air Conditioner Drip Bowl & Drip Pan Replacement Parts
Lennox Central Air Conditioner Duct & Venting Replacement Parts
Lennox Central Air Conditioner Engine Replacement Parts
Lennox Central Air Conditioner Fastener Replacement Parts
Lennox Central Air Conditioner Filter Replacement Parts
Lennox Central Air Conditioner Fuse, Thermal Fuse & Breaker Replacement Parts
Lennox Central Air Conditioner Gas Burner & Control Valve Replacement Parts
Lennox Central Air Conditioner Gasket & Seal Replacement Parts
Lennox Central Air Conditioner Grille & Kickplate Replacement Parts
Lennox Central Air Conditioner Handle Replacement Parts
Lennox Central Air Conditioner Heating Element Replacement Parts
Lennox Central Air Conditioner Hinge Replacement Parts
Lennox Central Air Conditioner Hose, Tube & Fitting Replacement Parts
Lennox Central Air Conditioner Igniter Replacement Parts
Lennox Central Air Conditioner Ignition Controls Replacement Parts
Lennox Central Air Conditioner Insulation Replacement Parts
Lennox Central Air Conditioner Latch Replacement Parts
Lennox Central Air Conditioner Leg, Foot & Caster Replacement Parts

Shop by Popular Lennox Central Air Conditioner Models

Lennox 10ACB30-9P Central Air Conditioner Parts
Lennox 10ACB48-10P Central Air Conditioner Parts
Lennox 10ACC-030-230-3 Central Air Conditioner Parts
Lennox 10ACC-030-230-4 Central Air Conditioner Parts
Lennox 10ACC-048-230-2 Central Air Conditioner Parts
Lennox 10ACC-060-230-2 Central Air Conditioner Parts
Lennox 13ACC-042-230-1 Central Air Conditioner Parts
Lennox 13ACD-024-230-1 Central Air Conditioner Parts
Lennox 13ACD-030-230-1 Central Air Conditioner Parts
Lennox 13ACD-030-230-2 Central Air Conditioner Parts
Lennox 13ACD-036-230-2 Central Air Conditioner Parts
Lennox HS29-024-1 Central Air Conditioner Parts
Lennox HS29-030-1 Central Air Conditioner Parts
Lennox HS29-030-2 Central Air Conditioner Parts
Lennox HS29-036-1 Central Air Conditioner Parts
Lennox XC25-036-230-3 Central Air Conditioner Parts
View more
Repair Clinic
Join Repair Clinic's VIP email list for 10% off, plus other discounts and tips!
Our Story

Family-owned and operated since 1912, Burke America Parts Group is the longest-running genuine appliance, HVAC, and outdoor power equipment parts solution in North America. At Repair Clinic, we're proud to be an international brand trusted by the pros as well as the DIY community.

About Repair Clinic
Customer StoriesRepair Parts BrandsDIY Repair BlogIn the News
Click for the BBB Business Review of this Appliances - Major - Parts & Supplies in Canton MI
Quick Links
Shipping Information365 Day Return PolicyRetail Location & HoursContact UsTrack OrderReviewsRepair Clinic Pro
Social Media
Privacy PolicyDo Not Sell/Share My Personal InformationTerms & ConditionsSitemapGet 10% Off
© 2026 RepairClinic.com