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Réparation d’une thermopompe centrale Lennox à Outremont
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Repair of a Lennox central heat pump in Outremont

A Lennox central heat pump in difficulty on a residential flat roof

At AirGreen , our technicians regularly work on Lennox HVAC systems installed on flat roofs of residential and commercial buildings in Montreal. Recently, we were called to Outremont to diagnose a Lennox central heat pump that was no longer providing heat despite the exterior fan apparently operating normally.

This installation, typical of Lennox single-compressor central heat pump systems, provided both heating and cooling for a renovated duplex. The unit, located on the building's flat roof, was exposed to wind, humidity, and extreme temperature fluctuations—demanding conditions that require rigorous maintenance.

Symptoms reported by the client

The client contacted us after noticing several worrying signs:

  • No heat in the ducts despite a thermostat set at 23°C;

  • Extended operation of the outdoor fan without stopping;

  • Frost buildup around the insulated refrigeration connection;

  • Abnormally high power consumption.

These clues suggested a failure of the refrigeration circuit or abnormal pressure in the compressor .

Diagnosis carried out by our AirGreen team

As soon as we arrived on site, we carried out a complete inspection:

1. Visual and safety check

  • Inspection of wiring, pipe insulation and securing of the unit to its treated wood supports.

  • Check clearance around the Lennox condenser to ensure adequate airflow.

2. Pressure and circuit integrity test

Using our pressure gauges and electronic detectors, we observed a partial loss of pressure in the R-410A refrigerant circuit , indicating a micro-leak at the main flare connection.

3. Electrical analysis

We then checked the power contactor and the starting capacitor , both in good condition. No short circuits or voltage imbalances were detected.

4. Compressor Inspection

The Lennox compressor was operating, but on a prolonged cycle, a direct result of the gas loss. This led to a drop in efficiency and a risk of overheating.

Repair and recommissioning

Our technicians undertook the complete repair according to the standards of the Quebec Building Code and LENNOX Authorized Service standards:

  1. Purge of residual refrigerant (safe recovery according to EPA standard).

  2. Renovation of the flare connection : clean cutting, replacement of the tube, tightening with controlled torque and addition of a high-pressure sealant.

  3. Nitrogen leak test : no leaks detected after 30 minutes.

  4. Complete vacuum to eliminate all moisture in the circuit.

  5. Recharge the system with the exact amount of R-410A according to the manufacturer's nameplate.

  6. System restart and balancing with subcooling and superheat measurement to optimize performance.

Result and improvement of comfort

After intervention, the Lennox central heat pump returned to its nominal performance:

  • Blowing temperature: 34°C in heating mode;

  • Balanced pressures: 118 psi (low) / 365 psi (high);

  • Stabilized electricity consumption.

The client immediately noticed a return to comfort and a significant reduction in outside noise . We also added additional insulation to the refrigeration line to prevent future freezing, especially during mild winters.

AirGreen Maintenance Tips

To extend the life of a Lennox central heat pump installed on a roof:

  • Clean the condenser coils at least twice a year;

  • Check the fastening of the refrigeration pipes before each winter;

  • Have the refrigerant charge checked by a certified technician;

  • Ensure good insulation of exposed fittings;

  • Schedule annual preventative maintenance with a specialized team like AirGreen.

Regular maintenance prevents efficiency losses and costly breakdowns, while ensuring optimal performance of the HVAC system, even in the middle of Montreal's winter.

Why choose AirGreen for your Lennox systems in Montreal

Our teams are authorized and trained on Lennox equipment , allowing us to perform accurate diagnostics, durable repairs and maintenance in accordance with manufacturer specifications.

Whether you are in Montreal, Laval, Longueuil, on the North Shore or the South Shore , AirGreen remains your trusted partner for any Lennox HVAC repair, installation or maintenance .

We guarantee a fast, transparent and professional service , so that your comfort is always optimal, whatever the external conditions.