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Error code reference

Denso Air Conditioner Error Code E20

DC voltage abnormality

Denso codesDenso air conditioner codes

DC voltage abnormality — DC voltage or current at or below, or at or above the specified value detected.

First step from the service manual

Check if the supplied voltage to the unit is unstable due to external influence, then RESET the controller. If error persists, replace the relay board and initialize the fan motor.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E20 means on a Denso air conditioner

The E20 error code on a Denso air conditioner signals a DC voltage abnormality, meaning the system has detected DC voltage or current levels that fall outside the acceptable operating range. This can manifest as a voltage reading that is too low, too high, or showing excessive fluctuation at a critical measurement point within the unit's power circuit. The control board continuously monitors these values to protect internal components, and when the readings deviate from specified thresholds, the system faults out and triggers this code.

The relay board is the primary component under scrutiny when E20 appears. This board is responsible for converting and distributing power to various subsystems, including the fan motor. If the relay board develops a fault, it can produce irregular DC output that the controller reads as an abnormality. Unstable incoming AC supply voltage from the building's electrical system is another common trigger, as poor power quality can translate into irregular DC levels after conversion inside the unit.

Diagnosis begins by ruling out external power supply issues before condemning any internal component. Voltage instability from the grid, undersized wiring, or shared circuits with heavy loads can all contribute to this fault. If a controller reset after confirming stable supply voltage does not resolve the error, the relay board should be replaced and the fan motor reinitialized. Fan motor initialization is required after relay board replacement to re-establish proper communication and operating parameters between the two components.

Source: manufacturer service documentation.

Common causes of E20

  1. 01

    Unstable or Poor Incoming Supply Voltage

    Wiring / connection

    Fluctuations or sags in the AC power supplied to the unit can cause irregular DC levels after internal conversion. Check for shared circuits with heavy loads, undersized wiring, or utility supply issues at the disconnect and service panel.

  2. 02

    Faulty Relay Board

    Part replacement

    The relay board can develop internal faults that cause it to output DC voltage or current outside the specified range. If the error persists after confirming stable supply voltage and performing a controller reset, the relay board is the primary suspect and should be replaced.

  3. 03

    Fan Motor Requiring Initialization

    Wiring / connection

    After a relay board replacement, or independently due to a communication fault, the fan motor may operate outside expected parameters and contribute to abnormal DC readings. Fan motor initialization is a required step following relay board replacement.

  4. 04

    Loose or Corroded Wiring Connections

    Wiring / connection

    Loose terminals or corroded wiring at the relay board or between the board and the fan motor can introduce resistance that distorts voltage and current readings. Inspect all connector terminals and wiring harnesses in the power circuit for signs of corrosion, heat damage, or poor seating.

  5. 05

    Controller Board Fault

    Part replacement

    In some cases the main controller board itself may misread DC voltage values due to an internal component failure. This is typically considered after the relay board has been replaced and the fan motor initialized without resolving the fault.

See the test procedure for each cause

Frequently asked questions about E20

What does E20 mean on a Denso air_conditioner?
E20 on a Denso air conditioner indicates a DC voltage abnormality. The system has detected DC voltage or current levels that are at or below, or at or above, the specified acceptable values. This causes the unit to fault and stop operating in order to protect internal components from damage.
Can I fix E20 on my Denso air conditioner myself?
The first step is to check whether the power supply to the unit is unstable, which may involve inspecting your electrical panel or the circuit feeding the unit. If the supply voltage is stable, you can attempt a controller reset. However, if the error returns, the repair requires replacing the relay board and reinitializing the fan motor, which are tasks best handled by a qualified technician with experience on commercial or mini-split systems.
Will resetting the controller clear the E20 error?
A controller reset may clear the E20 error temporarily if the root cause was a transient power supply fluctuation. However, if the fault is caused by a failing relay board or persistent voltage instability, the error will return after reset. A reset that does not hold is a strong indicator that a component repair or replacement is needed.
Is it safe to keep running my Denso AC with an E20 error?
The unit will typically shut itself down when E20 is triggered, so continued operation is usually not possible until the fault is cleared. Attempting to force the unit to run with an unresolved DC voltage abnormality risks damaging the relay board, fan motor, or other internal components. The fault should be diagnosed and resolved before resuming normal operation.
How much does it cost to repair a Denso E20 error?
Repair costs vary depending on the root cause. If the issue is simply unstable incoming power, correcting the electrical supply may involve minimal cost. If the relay board requires replacement, parts and labor combined typically range from a few hundred dollars to over five hundred dollars depending on the unit model and local labor rates. A diagnostic visit from a certified technician is recommended to confirm the fault before purchasing parts.

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