A service call in the middle of winter: when the cold puts heat pumps to the test
One particularly freezing January morning in Lachine , on the island of Montreal , our AirGreen team was dispatched to an emergency: a commercial building saw its Goodman central heat pumps stop producing heat while the outside temperature was close to -18°C .
On the building's flat roof, the two Goodman outdoor units were covered in frost and appeared to have completely shut down.
In these conditions, every minute counts. The client—a property manager responsible for several offices—was concerned about a prolonged outage that could cause the water pipes inside to freeze . At AirGreen, we're used to these winter emergencies typical of Greater Montreal , and we immediately began a comprehensive on-site diagnosis.
Initial Inspection: Excessive Frost and Blocked Compressors
Upon our arrival, our technicians noted that:
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The Goodman outdoor units were completely frosted over , a sign that the defrost cycle was no longer activating.
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The compressors would not start, although the control boards were receiving correct voltage.
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The outdoor temperature sensor displayed an inconsistent reading (-41°C), automatically blocking the heating function.
This type of problem is common in urban areas, where rooftop heat pumps are exposed to icy gusts and intense humidity, which can disrupt the thermal sensors.
In-depth diagnosis: a faulty temperature sensor and a frosted card
By dismantling the front of the units, our technicians were able to isolate the exact causes:
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Outdoor temperature sensor (thermistor) completely frozen and cracked.
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Defrost control board covered with a thin layer of internal ice, causing an intermittent short circuit.
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Clogged drainage system : Previous defrost water had accumulated and frozen under the base.
Using a controlled hot air defroster , we dried the components, replaced faulty sensors, and tested the board for electrical continuity.
Repair: precision and safety on a snowy roof
Our technicians, equipped with safety harnesses and heated gloves, carried out the following interventions:
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Complete replacement of the external thermal probes with genuine Goodman parts.
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Cleaning the electrical box and applying a protective dielectric sealant.
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Drainage repair with repositioning of PVC supports to prevent ice build-up.
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Automatic defrost cycle test : the compressor started running again and the discharge temperature quickly reached 46°C , confirming the return to normal.
Result: performance restored and customer reassured
After the repair, we let both Goodman units run for 45 minutes under observation.
The measures were optimal:
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Stable and balanced refrigerant pressure.
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Indoor blowing temperature at 30°C , stable and homogeneous.
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No abnormal frost after several cycles.
The client was able to see the complete restoration of its central heat pumps and the resumption of heating throughout the building.
We recommended that he install a partial snow shield and an anti-icing control system , which our AirGreen team can configure for buildings exposed to wind, as is often the case in Lachine , Dorval or Saint-Laurent .
Lessons Learned: The Importance of Winter Maintenance
This intervention illustrates a common problem in Quebec:
A poorly maintained or poorly defrosted heat pump can lose up to 40% of its heating capacity in the middle of winter.
To avoid this type of stoppage:
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Have your sensors and electronic boards checked before the cold season .
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Ensure efficient defrosting and drainage free from obstruction.
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Opt for AirGreen maintenance including cleaning, calibration and inspection of the refrigeration circuit.
Our teams respond quickly in Montreal, Laval, Longueuil , as well as on the North Shore and the South Shore , even in periods of extreme cold.
AirGreen: Your HVAC Partner for a Worry-Free Winter
With our expertise in Goodman , Lennox , Gree , Trane and Midea systems, we provide reliable and long-lasting service for both residential and commercial buildings .
Each intervention is carried out in compliance with the electrical and refrigeration standards in force in Quebec, guaranteeing safety and performance, even in the snow.
AirGreen — Experts in central heat pump repair and maintenance in Lachine and throughout Greater Montreal.