A service call for a Daikin heat pump that was no longer defrosting properly
At AirGreen , we regularly receive calls from owners of Daikin wall-mounted heat pumps in Montreal, especially during the changing seasons. Recently, our team was called to the Rosemont–La Petite-Patrie neighborhood for a Daikin unit installed on the back wall of a duplex, whose defrost system appeared to be faulty.
Background to the call
The customer contacted us after noticing that their outdoor unit remained covered in ice, even when the temperature was around -2°C, and that the flow of hot air inside was gradually weakening. The heat pump, a Daikin 12,000 BTU Aurora series , had been operating normally since its installation approximately five years ago.
First on-site inspection
Our technician quickly arrived on site. The outdoor condenser, mounted on galvanized steel wall brackets , was clear and clean, which immediately ruled out the possibility of an airflow blockage.
We then carried out several checks:
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Operating mode : the system remained stuck in heating mode without ever activating defrosting.
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Refrigeration pressure reading : slightly too low for ambient temperature.
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Defrost sensor (thermistor) inspection : The resistance was unstable and the returned values were not within the normal range expected by Daikin.
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Control card : no visual damage, but a defrost signal not triggered, confirming that the probe was faulty.
Diagnosis confirmed: defective defrost thermistor
The thermistor is a small sensor that measures the temperature of the outdoor coil. When it sends incorrect data, the system cannot detect ice formation, which prevents the automatic defrost cycle . This defect, although minor in appearance, can cause in the long term:
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a significant drop in performance ;
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overconsumption of energy ;
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and premature wear of the compressor .
Repair carried out by our AirGreen team
Our technician proceeded methodically:
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Safely disconnect the heat pump's power supply .
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Disassembly of the casing to access the coil and the thermistor.
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Replacement of the temperature sensor with an original Daikin part.
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Resistance test using a digital multimeter to confirm the accuracy of the new part.
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System restart and forced defrost simulation using service mode.
After the repair, the heat pump initiated a complete defrost cycle lasting a few minutes, removing the ice accumulated on the fins. At the end of the cycle, the indoor discharge temperature quickly climbed to 41°C , indicating a return to normal performance.
Advice given to the client
In order to prevent the problem from recurring, we recommended to the customer:
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Have your system inspected every fall , before the start of the heating season.
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Keep the condenser free of any obstructions , such as leaves, snow or ice.
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Allow the heat pump to complete its cycles without manually turning it off during defrosting.
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And consider a complete biannual maintenance , especially if the system operates year-round.
AirGreen expertise: precision and efficiency
This type of intervention highlights AirGreen's specialization in repairing Daikin systems and other popular brands of wall-mounted heat pumps in Montreal. Our technicians are trained on the latest generation of products running on R-32 refrigerant , and use digital diagnostic tools to quickly identify anomalies.
We operate daily in the residential neighborhoods of Rosemont, Outremont, Plateau-Mont-Royal, Côte-des-Neiges and Ville-Marie , as well as in Laval, Longueuil, on the North Shore and the South Shore . Each repair is carried out with the attention to detail and transparency that AirGreen is known for.
Final result: restored comfort and regained efficiency
After the repair, the customer noticed an immediate return of heating and a reduction in indoor blower noise . His Daikin heat pump is now fully operational, ready to handle the temperature fluctuations of Montreal's spring.
This type of intervention clearly illustrates our commitment: to offer a fast, reliable and long-lasting service , always supported by precise diagnostics and original parts.