Denso Air Conditioner Error Code AL

The AL code means the Denso air conditioner has received a stop signal from a connected fire alarm system and has shut down as a safety measure. This is an intentional interlock function, not a unit malfunction. The air conditioner will remain off until the fire alarm signal is cleared and the unit is manually reset. Once the alarm condition is resolved, press and hold the SET TEMP UP and SET TEMP DOWN buttons at the same time for 3 seconds to reset the unit.

Yes, the AL code should always be taken seriously because it means a fire alarm system has signaled the air conditioner to stop. Before resetting the unit, you should confirm there is no active fire or smoke condition and that the fire alarm system has been properly cleared by authorized personnel. Never bypass or ignore this interlock.

If the AL code is caused by a legitimate fire alarm trigger that has since been cleared, the reset costs nothing beyond the technician time to perform it. If faulty wiring between the fire alarm panel and the AC unit is responsible, repair costs can range from around 75 to 250 dollars depending on the extent of the wiring work needed. If the fire alarm control panel itself requires service or replacement, costs will be higher and will depend on a licensed fire alarm contractor's assessment.

First, confirm that the fire alarm system has been fully cleared and is no longer sending a stop signal to the AC unit. Once the fire alarm signal is off, press and hold the SET TEMP UP and SET TEMP DOWN buttons simultaneously for 3 seconds to reset the AL code. If the code returns immediately after the reset, the fire alarm system or its wiring to the AC unit still requires attention.

The reset will clear the AL code only if the underlying fire alarm signal has been deactivated. If the fire alarm panel is still in a triggered state, or if there is a wiring fault causing a false signal at the AC input terminal, the AL code will return after the reset. Persistent AL codes require investigation of the fire alarm system and its interconnecting wiring, not repeated resets of the air conditioner.