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Error code reference

Denso Air Conditioner Error Code FL

Overcurrent relay (thermal relay) protection activated

Denso codesDenso air conditioner codes

Overcurrent relay (thermal relay) protection activated — overcurrent relay contact opened due to fan motor overcurrent condition.

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What FL means on a Denso air conditioner

The FL error code on a Denso air conditioner indicates that the overcurrent relay, also referred to as a thermal relay, has been activated. This protective device monitors current flow through the fan motor circuit and is designed to open its contact when it detects a current level that exceeds the motor's rated operating range. When the relay contact opens, the fan motor loses power and the control board registers the FL fault to halt system operation and prevent further damage.

The thermal relay functions as both a current-sensing and heat-sensing protective device. As excessive current flows through the fan motor windings, the relay's internal bimetallic element heats up and mechanically opens the circuit. This can occur due to a motor that is drawing too much current because of worn bearings, degraded winding insulation, a seized rotor, or a capacitor that is failing and unable to provide proper starting torque. The relay will not reset until it cools down and the underlying cause is addressed.

Common conditions that lead to FL activation include blocked or obstructed fan blades, a failing run capacitor on the fan motor, deteriorated motor bearings causing mechanical drag, or actual motor winding failure. In some cases, low voltage supply to the unit can also cause the motor to draw elevated current as it struggles to maintain speed. Technicians should inspect the full fan motor circuit, including the capacitor, blade assembly, and motor windings, before attempting to restore operation.

Source: manufacturer service documentation.

Common causes of FL

  1. 01

    Failing or failed fan motor capacitor

    Part replacement

    A degraded run capacitor cannot provide the phase shift needed for proper motor startup and operation, causing the motor to draw excessive current. Measure capacitor microfarad value with a capacitor meter and compare to the rated value printed on the capacitor body.

  2. 02

    Worn or seized fan motor bearings

    Part replacement

    Bearing wear increases mechanical drag on the motor rotor, forcing the motor to draw higher current to maintain rotation. Inspect for unusual noise during operation and check that the fan spins freely by hand when power is off.

  3. 03

    Obstructed or jammed fan blade

    Wiring / connection

    Debris, ice buildup, or a loose blade contacting the housing can restrict fan rotation and spike motor current. Visually inspect the fan assembly and blade clearances with power disconnected.

  4. 04

    Fan motor winding failure

    Part replacement

    Shorted or grounded windings inside the motor cause a dramatic increase in current draw and will repeatedly trip the thermal relay. Check winding resistance across motor terminals and compare phases for balance; a shorted winding will show very low or near-zero resistance.

  5. 05

    Low supply voltage to the unit

    Wiring / connection

    Insufficient line voltage forces the motor to draw higher current to compensate for reduced power delivery. Measure supply voltage at the unit's disconnect or terminal block under load conditions and confirm it is within the unit's rated input voltage range.

See the test procedure for each cause

Frequently asked questions about FL

What does FL mean on a Denso air_conditioner?
The FL code on a Denso air conditioner means the overcurrent relay, also called a thermal relay, has tripped due to excessive current in the fan motor circuit. The relay opens its contact to cut power to the fan motor and protect the system from damage. This is a protective fault that requires diagnosis of the fan motor and related components before the unit can resume normal operation.
Can I reset the FL error code myself to get the unit running again?
The thermal relay will reset on its own once it cools down, and the FL code may clear temporarily after a reset. However, if the underlying cause is not corrected, the relay will trip again and the fault will return. Repeatedly cycling the unit without fixing the root cause can accelerate motor failure and risk additional component damage.
Is it safe to keep running my Denso air conditioner when the FL code appears?
No, it is not safe to continue operating the unit while the FL code is active. The system has shut down specifically to prevent motor overheating and potential electrical damage. Running the unit repeatedly through reset cycles without addressing the cause can lead to more extensive and costly repairs.
How much does it cost to repair a Denso air conditioner with an FL error code?
Repair costs depend entirely on which component has failed. A replacement run capacitor is typically a low-cost repair in the range of $50 to $150 including labor. A failed fan motor replacement can range from $200 to $600 or more depending on the unit model and labor rates in your area. Diagnosing the specific fault first will prevent unnecessary parts replacement.
Will clearing the FL code fix the problem on my Denso air conditioner?
Clearing or resetting the FL code does not fix the underlying problem. The thermal relay trips in response to a real overcurrent condition, so the code will return if the fan motor, capacitor, or supply voltage issue is not corrected. A proper repair requires identifying and resolving the cause of the excessive current draw before the system can operate reliably.

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