A service call in the middle of winter in Laval
At AirGreen , we know that a heat pump breakdown in the winter can quickly become an emergency. This is exactly what happened during a call received in Sainte-Dorothée, Laval , for a Mestec central heat pump installed outside a single-family home. The customer had noticed that the system had not been producing enough heat for two days, despite the fact that the heat pump was still running intermittently. A layer of snow had accumulated on top of the condenser , a typical sign of a problem related to the defrost cycle .
On-site diagnosis: between ice and defrosting failure
Upon our arrival, our technician performed a complete inspection of the Mestec condenser . The model in question, a unit of approximately 36,000 BTU , was mounted on a wall bracket, which made it easy to access despite the accumulation of snow on the ground.
Initial checks revealed:
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A thick layer of frost on the rear grille of the condenser.
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The outdoor fan was spinning erratically.
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The discharge temperature indicated abnormally low pressure for a heating cycle.
After some testing, our team confirmed that the electronic defrost board was faulty. This component, essential to the proper operation of a heat pump in winter, normally prevents excessive ice buildup on the coils by briefly reversing the refrigeration cycle.
Intervention: card replacement and complete recalibration
We replaced the defrost board with a new, Mestec-compatible part. Before installation, the technician took care to:
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Disconnect the main power supply and secure the work area.
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Check the continuity of the temperature sensors (evaporator and compressor).
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Clean the control box and remove any moisture.
Once the board was replaced, the system was restarted and run through a controlled defrost cycle . The compressor restarted normally, the pressure stabilized, and the accumulated ice began to gradually melt.
We also have:
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Cleaned the condenser coils with gentle steam to optimize heat transfer.
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Repositioned the cables and sealed the electrical entries to prevent water infiltration.
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Checked the indoor thermostat was working properly, to ensure the defrost control was properly synchronized.
Result: restored comfort and optimal performance
As soon as the intervention was completed, the indoor temperature began to rise steadily. Within minutes, the Mestec system was once again providing uniform and stable heat throughout the residence.
We advised the client:
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Regularly check the accumulation of snow on top of the condenser, especially after heavy rainfall.
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Leave a clearance of at least 60 cm around the unit to ensure good air circulation.
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Schedule annual preventive maintenance before each winter, which helps extend compressor life and prevent defrost failures.
What this repair demonstrates
This case illustrates the importance of regular professional maintenance for central heat pumps installed in Quebec , where winter conditions put HVAC systems to the test.
At AirGreen , we work daily on systems from various brands— Midea, Gree, Lennox, Fujitsu, Sharp, Mestec , and many others—for repairs ranging from refrigerant leaks to the complete restoration of an electrical circuit .
Our certified technicians ensure that each intervention aims not only to repair, but to optimize the energy performance of the system, while guaranteeing the electrical safety and interior comfort of our customers.
Intervention carried out by AirGreen – HVAC Service in Laval
By choosing AirGreen, you benefit from:
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Certified and experienced technicians in central and wall-mounted heat pumps.
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Fast service in Laval, Montreal, Longueuil, North Shore and South Shore.
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Original parts and manufacturer's warranties .
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Precise diagnosis with digital instruments (manometers, thermocouples, pressure readers).
Thanks to our expertise, the Sainte-Dorothée client now benefits from reliable thermal comfort and a Mestec system ready to face the coldest months of the Quebec winter.