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Réparation d’une thermopompe murale Lennox à Rosemont–La Petite-Patrie
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Repair of a Lennox wall-mounted heat pump in Rosemont–La Petite-Patrie

A quiet outdoor unit: the signal of a compressor running out of steam

When a client in Montreal's Rosemont–La Petite-Patrie neighborhood called us about a Lennox wall-mounted heat pump that was no longer producing heat or cooling, our team of AirGreen experts knew it was likely a serious problem with the refrigeration circuit . Located on a brick back wall, the installation had been done several years ago and had been working flawlessly until then.

Upon arrival, we found that the compressor would not start , although the indoor and outdoor fans appeared to be receiving power correctly. This type of symptom is often related to a compressor not starting , either due to a faulty electronic board or a worn power relay .

Diagnosis: electrical check and compression test

Our technicians carried out a series of tests:

  • Voltage check at the main power supply of the outdoor unit;

  • Compressor resistance measurement ;

  • Inspection of the Lennox control board , where slight blackening indicated a past short circuit;

  • Direct compressor testing using a temporary starter module.

The compressor responded well to the manual test: the problem was therefore with the control board and not the compressor itself. This good news prevented a major replacement, which reassured our customer.

Intervention: replacement of the card and repowering of the system

We have :

  1. Turn off the power and remove the original Lennox electronic board;

  2. Install a new compatible card , programmed according to the model specifications;

  3. Clean oxidized connectors and secure wiring to prevent future vibrations;

  4. Restart the heat pump and monitor the heating and cooling cycles for more than 20 minutes.

The unit returned to normal operation, with stable pressure and energy efficiency within manufacturer standards.

Interview and observations

While observing the installation, we noticed that the Lennox outdoor unit was mounted on a wall bracket above a patio door —a common fixture in Montreal alleys and backyards. This type of installation requires rigorous maintenance: dust and urban debris can clog the condenser fins and reduce heat exchange efficiency .

We took advantage of the intervention to:

  • Clean the fins with compressed air ;

  • Check clearance around the unit to ensure good air circulation;

  • Tighten the wall bracket fasteners , which are subject to thermal expansion and seasonal vibrations.

AirGreen Tips for Urban Facilities

In dense neighborhoods like Rosemont, where outdoor units are often installed near walls or in interior courtyards:

  • Make sure to leave at least 30 cm of free space around the unit to avoid overheating;

  • Schedule a complete annual maintenance including coil cleaning, drain checking and refrigerant pressure measurement;

  • Watch for unusual noises (humming, clicking, vibrations), often the first signs of wear on a relay or fan.

Result: a refurbished Lennox system and a satisfied customer

After the system was fully restarted, the customer immediately noticed a return to thermal comfort in his apartment. The indoor temperature stabilized in less than an hour, and the unit's noise level was remarkably low—proof of optimal operation.

At AirGreen , we believe that every repair is an opportunity to improve the overall performance of your HVAC system. With our expertise and diligence, we extend the lifespan of your equipment while optimizing its energy efficiency.