Lennox Central HVAC System Repair in Sainte-Thérèse

A service call on a flat roof that reveals a complex failure

At AirGreen , we often work on complex commercial and residential HVAC systems. Today's service call took us to Sainte-Thérèse , on Montreal's North Shore , for an in-depth diagnosis of a central Lennox system installed on the roof of a modern apartment building.

The client reported a lack of air conditioning in several units of the building, despite the system appearing to be functioning. The unit in question—a dual-compressor Lennox rooftop —was responsible for servicing all of the block's air ducts.

---

Initial diagnosis: compressor failure and electrical problem

Upon opening the control panel, our technicians immediately noticed several telltale signs:

• Loose wires and slightly blackened insulation in the control compartment.

• Internal circuit breakers tripped , indicating a previous electrical overload.

• The main compressor appeared to be inactive despite the thermostat request.

Using a professional multimeter , we checked the voltage on the compressor and relay terminals. The result: the main contactor was no longer engaging properly, preventing the compressor from starting.

---

Step 1 – Inspect the electrical circuit and starting components

The problem was caused by a faulty power relay and a weak start capacitor . Both of these are essential for the compressor to function properly.

We have proceeded to:

• Replacing the power relay with a genuine Lennox part.

• Installation of a new dual capacitor , calibrated for the compressor and the fan.

• A complete check of the wiring to ensure that no oxidation or poor contact persists.

---

Step 2 – Checking the refrigeration circuit

After power was restored, the compressor started, but the suction pressure indicated an abnormally low refrigerant level . A visual inspection revealed traces of oil on a brazed connection in the circuit—a typical sign of a microleak .

So we have:

• Performed a nitrogen pressure test to locate the leak.

• Repaired the leaking solder joint .

• Pulled a full vacuum to -500 microns to remove all moisture.

• Recharged the system with R-410A according to the manufacturer's specifications.

---

Step 3 – Performance optimization and system calibration

Once the charge was restored, we carried out a series of tests:

• Monitoring of pressures and temperatures using a pressure gauge and thermocouple.

• Measurement of subcooling and superheat to ensure optimal performance.

• Checking the air flow at the duct outlet.

The results were perfect:

• Stable suction pressure at 118 psi.

• Air blown at 14°C colder than ambient air.

• Electricity consumption returned to normal.

---

Final result: comfort restored and prevention assured

After the repair, air conditioning was fully restored throughout the building . The property manager immediately noticed the difference.

Before leaving the premises, our team:

• Cleaned the electrical compartment.

• Tighten all connections.

• Recommended a seasonal preventive inspection to avoid the return of a breakdown related to humidity or vibration.

---

Why choose AirGreen for your HVAC systems on the North Shore

At AirGreen, we know that rooftop units require advanced technical expertise . Our technicians are trained to:

• Quickly diagnose electrical and refrigeration faults.

• Safely handle R-410A and R-32 refrigerant gases .

• Repair or replace original manufacturer parts .

Thanks to our rapid interventions in Sainte-Thérèse, Laval, Montreal and on the South Shore , we provide reliable and long-lasting HVAC service , supported by our certified know-how.

---

AirGreen – Air Conditioning and Heating , your trusted partner for all your Lennox central HVAC system repair needs, whether you are on the North Shore , the South Shore or in the Montreal metropolitan area .