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Lennox Central air conditioner not cooling properly

If your Lennox central air conditioner is not cooling properly, start with the furnace main control board, especially if the condensing unit contactor is not receiving 24 volts or the blower motor has no power. Next, check for an airflow problem: a clogged air filter, blocked registers, or dirty blower wheel can restrict air, cause the evaporator coil to freeze, and leave your central air not cooling or air conditioner blowing warm air. A failed contactor can prevent the outdoor condensing unit from receiving power, while a defective dual run capacitor may make the condenser fan motor noisy, cause it to overheat, or keep it from running. If airflow is good, the coils are clean, and the blower, fan, and compressor run but the AC is still not cold, a refrigerant leak or restriction in the sealed system is likely. A faulty relay board can also keep the blower motor from receiving power. Turn off power before inspecting parts, and leave 240V testing or replacement to a qualified technician. Any refrigerant or sealed-system repair requires EPA 608 certification. Enter your Lennox model number to find the exact replacement part for your central air conditioner.

01 - Lennox Central Air Conditioner Main Control Board

If the central air condensing unit contactor is not receiving 24 volts or power is not getting to the furnace blower motor, a possible cause is a defective furnace main control board. While this is not a common problem, if all other potentially faulty components are working properly, the main control board should be replaced.
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Top Solution

02 - Air Flow Problem

Proper air flow is critical for the central air conditioner to work properly. The evaporator needs proper air flow to keep the condensing water from freezing. If the air filter or blower wheel gets clogged, ice can start forming on the evaporator coils, eventually freezing them up and preventing proper air flow. It is recommended to replace the air filter at least every 6 months or sooner depending on the conditions. Refer to owner's manual for guidance. Avoid covering registers with furniture, rugs, or other items that will restrict the air flow.
Top Solution

03 - 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 is defective, it will not provide voltage to the condensing unit. To determine if the contactor is at fault, use a multimeter to test the contactor for continuity. If the contactor does not have continuity, replace it.
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Highly Likely

04 - Lennox Central Air Conditioner Dual Run Capacitor

If the dual run capacitor is defective, the fan motor might be noisy, overheat, or not run at all. To determine if the dual run capacitor has failed, inspect the capacitor. If the dual run capacitor is bulging or leaking, replace it.
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Highly Likely

05 - Sealed System Problem

If the unit has good air flow, the evaporator and condensing unit coils are clean, the fan and compressor are running, and the furnace blower is on, but there is still not enough cooling, it is likely there is a leak or restriction in the sealed system. Since diagnosing and repairing a sealed system takes specialized tools and knowledge, a qualified service technician should diagnosis and repair the unit.
Highly Likely

06 - Lennox Central Air Conditioner Relay Board

A relay board is often used to control components of an a central air condidtioner. If the blower motor is not receiving power, the relay board is likely the cause. A defective relay board will need to be replaced.
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Common

Frequently Asked Questions

Why is my Lennox central air conditioner not cooling properly?
Why is my central AC coil freezing up or not blowing enough air?
What should I check if the Lennox condenser fan is not spinning or the outdoor AC unit is not running?
Why is my air conditioner making a loud noise or is the condenser fan making noise?
How do I find the correct Lennox central air conditioner part?

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