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Error code reference

Denso Air Conditioner Error Code AS

Condensate pump problem

Denso codesDenso air conditioner codes

Condensate pump problem — optional condensate pump is damaged or broken (J8 input of relay board turns to open).

First step from the service manual

Fix the condensate pump, then reset the system by pressing ON/OFF and HI/LO buttons simultaneously for 5 sec.

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

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What AS means on a Denso air conditioner

The AS error code on a Denso air conditioner indicates a problem with the optional condensate pump. This pump is responsible for removing condensate water that collects during the cooling process, particularly in installations where gravity drainage is not possible and water must be pumped to a drain location. The system monitors the pump's operational status through the J8 input on the relay board. When the relay board detects that the J8 input has shifted to an open state, it interprets this as a pump failure and triggers the AS fault code to halt operation and prevent water damage.

The J8 input on the relay board serves as the communication point between the condensate pump and the main control system. Under normal operation, this circuit remains closed, confirming the pump is functional. A transition to an open state at J8 can indicate a broken pump motor, a failed float switch within the pump assembly, a wiring disconnection, or physical damage to the pump unit itself. Since the condensate pump is described as an optional component, this fault will only appear in systems where the pump has been installed and wired into the relay board.

To clear the AS code, the underlying pump issue must be resolved first. Simply resetting the unit without addressing the pump will not permanently clear the fault. Once the pump has been repaired or replaced, the system reset is performed by pressing the ON/OFF and HI/LO buttons simultaneously and holding them for 5 seconds. This action clears the stored fault state from the relay board and restores normal operation.

Source: manufacturer service documentation.

Common causes of AS

  1. 01

    Failed condensate pump motor

    Part replacement

    The pump motor itself may have burned out or seized, causing the J8 circuit on the relay board to open. Check if the pump makes any sound or draws power when the unit calls for drainage.

  2. 02

    Tripped or faulty float switch

    Wiring / connection

    Most condensate pumps include an internal float switch that opens the circuit when the reservoir is full or the switch fails. Inspect the pump reservoir for standing water and check whether the float switch resets after draining.

  3. 03

    Wiring disconnection at J8 relay board input

    Wiring / connection

    A loose, corroded, or broken wire connection at the J8 input of the relay board can cause the system to read an open circuit even if the pump itself is functional. Inspect the wiring harness running from the pump to the relay board.

  4. 04

    Physical damage to the pump unit

    Part replacement

    The pump housing or internal components may be cracked or broken due to impact, freezing water, or age-related wear. Visually inspect the pump body for cracks, leaks, or signs of mechanical damage.

  5. 05

    Blocked or frozen condensate line causing pump overload

    Wiring / connection

    A clogged discharge line can prevent the pump from moving water, causing it to overheat or trip an internal protection switch. Inspect the discharge tubing for blockages, kinks, or ice buildup.

See the test procedure for each cause

Frequently asked questions about AS

What does AS mean on a Denso air conditioner?
The AS code on a Denso air conditioner indicates a condensate pump problem. Specifically, the relay board has detected that the J8 input, which monitors the optional condensate pump, has shifted to an open state. This means the pump is damaged, has failed, or has lost its electrical connection to the relay board. The unit will not operate normally until the pump issue is resolved.
Can I fix the AS error code myself?
Some causes of the AS code are within reach of a knowledgeable DIYer, such as clearing a blocked condensate line, draining a full pump reservoir, or reseating a loose wiring connection at the J8 relay board input. However, replacing a failed pump motor or diagnosing internal relay board faults typically requires a qualified technician. After any repair, the system must be reset by pressing the ON/OFF and HI/LO buttons simultaneously for 5 seconds.
Will resetting the unit clear the AS error code?
Resetting alone will not permanently clear the AS code if the underlying pump problem has not been fixed. The reset procedure, pressing ON/OFF and HI/LO simultaneously for 5 seconds, is intended to be performed after the condensate pump has been repaired or replaced. If the fault condition still exists at the J8 input, the code will return immediately or shortly after the reset.
Is it safe to continue using my air conditioner when the AS code is displayed?
No, you should not attempt to operate the unit while the AS code is active. A non-functioning condensate pump can allow water to accumulate and overflow, potentially causing water damage to ceilings, walls, or floors. The system is designed to shut down when this fault is detected specifically to prevent that damage. Address the pump issue before resuming operation.
How much does it cost to repair the AS error code on a Denso air conditioner?
Repair costs vary depending on what has failed. A simple line clearing or wiring fix may involve only a service call fee, typically in the range of $75 to $150. Replacing a condensate pump unit generally costs between $150 and $400 including parts and labor, depending on the pump model and local labor rates. Relay board repairs or replacements can be more expensive, potentially ranging from $300 to $600 or more.

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