Rapid intervention for a wall-mounted air conditioner that has completely stopped
At AirGreen , we often receive calls from surprised customers who find their wall-mounted air conditioner no longer works for no apparent reason. This is exactly the situation we encountered during our recent intervention in Ville Mont-Royal , where a Sharp wall-mounted air conditioner stopped working overnight, leaving the apartment without air conditioning despite the heat outside.
Background to the breakdown
The customer contacted us after several unsuccessful restart attempts. The indoor unit displayed an error code “88” , indicating a communication fault between the wall unit and the outdoor compressor. This type of error is typical of an electronic failure , but it can also be caused by a loose connection or a damaged control board .
Upon arrival, we found a Sharp wall unit installed properly, but with its front panel open and electrical terminals partially disconnected . A first visual inspection showed traces of dust and slight oxidation on the connectors.
Step 1 – Initial Analysis and Diagnosis
Our technicians started by:
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Check electrical continuity between the indoor unit and the outdoor condenser.
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Inspect the main board for burn marks or overheating.
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Analyze the communication signals on terminals 1-2-3 of the wall terminal.
Multimeter measurements revealed unstable voltage on the communication wire. This indicated a poor contact at the internal terminal block , probably due to slight oxidation caused by repeated condensation near the coil.
Step 2 – Cleaning and Tightening Connections
We have carefully:
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Unplugged the unit.
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Cleaned the terminals with a dielectric contactor product.
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Tightened all screws on the main terminal block.
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Checked the polarity and exact correspondence between the inner and outer wires (1-2-3).
After completing these steps, the communication signal became stable again, and the unit reset properly. However, a second test revealed that the indoor fan still would not start, despite correcting the wiring.
Step 3 – Further Diagnosis: Fan Control Module
We removed the top cover to access the BLDC motor control module . Using our Sharp diagnostic interface, we confirmed that the module's power transistor had failed, preventing the motor from starting despite the correct input voltage.
This type of failure is common on units over 8 years old, especially when dust accumulates around the motor and Hall sensor. We therefore proceeded to completely replace the control module with a genuine Sharp part, conforming to the AY-XC09KR series.
Step 4 – Restart and Checks
Once the card was replaced, we carried out:
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A start-up test in cooling mode .
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A check of the blowing temperature (which dropped to 11°C in less than 4 minutes).
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Airflow and fan speed control .
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A visual inspection of the condensate drain to ensure there were no leaks.
The air conditioner was working perfectly at the end of our intervention. We then closed and cleaned the unit, before returning the system to automatic mode.
Step 5 – Preventive Maintenance Tips
We recommended to the client:
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Have the filters cleaned every two weeks during the hot season.
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Avoid leaving the unit inactive for too long without power, as internal moisture can promote oxidation.
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To plan annual professional maintenance to ensure the durability of the electronic module.
Results and customer satisfaction
Thanks to our quick and precise intervention , the Sharp air conditioner in Ville Mont-Royal has regained all its original performance. The customer immediately noticed a reduction in noise , increased thermal stability , and above all, a constant and powerful cold blast .
This case perfectly illustrates the value of a rigorous diagnosis , where every detail counts: a simple loose terminal or a worn card can immobilize an entire system.
At AirGreen , we operate every day in Montreal , Laval , Longueuil , on the North Shore and the South Shore to diagnose, repair and maintain all types of residential and commercial HVAC systems — whether it's a wall-mounted heat pump , a Sharp air conditioner , or a MultiZone installation .
We combine technical expertise, genuine parts and fast service to guarantee optimal comfort in all seasons.