When a wall-mounted heat pump stops heating in the heart of Montreal
In Montreal's bustling Rosemont–La Petite-Patrie neighborhood, a customer contacted us after noticing that her Midea wall-mounted heat pump was no longer heating properly, even though the indoor fan seemed to be operating normally. The problem occurred mid-season, when the system was supposed to alternate between heating and cooling—a time that's often critical for wall-mounted units that undergo numerous defrost cycles.
Upon our arrival, our AirGreen technician noticed that the outdoor unit, securely installed on a galvanized steel wall bracket , showed signs of residual frost on the coil, despite an outside temperature above zero. This detail already pointed the diagnosis towards a problem with the defrost sensor or communication between the electronic boards.
Initial inspection: complete analysis of system behavior
Our first step was a complete electrical and functional check :
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Correct 240V power supply confirmed,
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Communication cable intact,
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Compressor inrush current within normal limits,
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Cooling pressures slightly lower than average for heating mode.
The customer also mentioned noticing a slight vibration and a change in blowing noise before the heater failed completely. After observing the cycle, we found that the compressor was stopping prematurely : the control board was receiving a false end-of-defrost signal, interrupting the heating mode too early.
Diagnosis confirmed: faulty defrost sensor
By accessing the main board of the Midea Xtreme Series heat pump , our technician checked the resistance of the outdoor temperature sensor (thermistor). The reading was 18 kΩ at 5 °C—a figure that was too high according to the manufacturer's specifications (approximately 10 kΩ at this temperature). The faulty sensor was therefore sending a false reading to the board, causing the heating cycle to stop prematurely and preventing the heat pump from maintaining the desired temperature.
Intervention: replacement and recalibration
In order to restore proper functioning, we have taken the following steps:
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Replacing the defrost sensor with a genuine Midea part, carefully attached to the outdoor coil,
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Cleaning the coil using a biodegradable cleaner to remove deposits and optimize heat exchange,
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Checking compressor connections and control cables,
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Complete system restart and control of defrost cycles,
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Measurement of discharge and suction temperatures , confirming stable performance and compliance with standards.
The system resumed normal operation with an indoor blowing temperature of 46°C , guaranteeing immediate comfort for the customer.
AirGreen Finishing and Recommendations
We also checked the stability of the wall mount , which is essential to avoid vibrations and extend the life of the equipment. This Midea model had been installed about 2.5 meters from the ground, under the eaves, a wise position to protect it from snow and water.
Before leaving the premises, our technician recommended to the customer:
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To have the internal filters cleaned every 4 to 6 weeks,
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To have the probes and pressures inspected every year before winter,
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Avoid covering the outdoor unit during the mid-season, so as not to impair ventilation.
AirGreen Expertise in Montreal: Fast and Accurate Service
This intervention perfectly illustrates the rigor and precision of our AirGreen teams in the repair of residential HVAC systems in Montreal . Midea wall-mounted heat pumps , renowned for their efficiency and low-temperature performance, require precise maintenance to maintain their maximum performance.
Our certified technicians operate in Montreal, Laval, Longueuil, the North Shore, and the South Shore , providing fast, professional, and long-lasting service. Each repair is performed using genuine parts and validated through a comprehensive performance check.
Thanks to our intervention, the Rosemont–La Petite-Patrie client regained the comfort and reliability of her system, just in time for the cooler evenings.