As temperatures drop during winter in Québec, it’s common to notice a layer of frost forming on your heat pump’s outdoor unit. But not all cases are the same. Some are perfectly normal and even expected as part of the system’s cycle, while others may indicate an underlying issue that could impact your HVAC system’s performance, increase your energy consumption, and eventually damage the unit.
At AirGreen, we’ve responded to many calls in Montréal, Laval, Longueuil, the North Shore, and the South Shore for issues related to excessive frost. Here’s everything you need to know to identify what’s going on, respond appropriately, and above all, prevent frost from becoming an obstacle to your winter comfort.
Frost on a Heat Pump: Normal Phenomenon or Sign of Trouble?
A heat pump in heating mode draws heat from the outside air and transfers it indoors. During this process, the outdoor unit may accumulate ambient moisture, which freezes upon contact with the coils.
What’s normal:
-
A thin white layer of frost on the coils
-
Temporary appearance followed by an automatic defrost cycle
-
Soft “blowing” sound during defrost
-
Some condensation or light runoff afterward
What’s not normal:
-
A thick or persistent layer of ice
-
Complete blockage of the outdoor fan
-
The unit no longer heating properly
-
Defrost cycles happening too frequently or not at all
Real Case Study: Excessive Frost in Repentigny on a Lennox EL18XPV Unit
A client from the North Shore called us after noticing their Lennox EL18XPV central heat pump wasn’t heating efficiently even though the outdoor temperature was only -5°C. When our technician arrived on-site, they observed:
-
A thick layer of ice covering the coils
-
The automatic defrost system wasn’t functioning
-
The outdoor unit was installed in a poorly ventilated corner
-
Plant debris was blocking airflow
After a thorough cleaning, reactivating the defrost system, and relocating the unit to a more open area, performance was restored.
Common Causes of Abnormal Frost
1. Blocked Airflow
Debris, dead leaves, snow, or clutter around the unit prevent proper airflow, which accelerates frost buildup.
2. Faulty Defrost Sensor
If the sensor is improperly placed or defective, it may not trigger the defrost cycle correctly.
3. Poor Initial Installation
A unit that’s poorly oriented, installed too close to a wall, or lacking ventilation space increases the risk of freezing.
4. Extreme Weather Conditions
A mild thaw followed by a quick freeze creates surface water that instantly turns to ice.
5. Lack of Maintenance
A dirty coil, bent fins, or a clogged fan reduce system efficiency and slow natural defrosting.
What to Do If You See Frost on Your Outdoor Unit
Here are the steps recommended by AirGreen:
-
Check the immediate surroundings: is the unit clear on all sides?
-
Monitor cycle frequency: is your heat pump regularly switching to defrost mode?
-
Gently clear any debris or snow from around the unit (no sharp tools!)
-
Pay attention to indoor temperature: if it’s no longer stable, it’s time to act
-
Call AirGreen for a full inspection
How to Prevent Excessive Frost Formation
-
Ensure proper installation: at least 12 to 24 inches of clearance around the unit
-
Install a snow shield to protect from snowfall and freezing rain
-
Schedule fall maintenance: coil cleaning, sensor check, system inspection
-
Use a smart thermostat to optimize system cycles
-
Choose models built for cold climates, such as the Bosch BOVA, Gree Elite, or Fujitsu KZAH R-32
Why Choose AirGreen?
-
A team trained for Québec winters
-
Over 1,000 successful installations in Greater Montréal
-
Recommended annual preventative maintenance
-
Fast diagnostics and repairs within 48 hours
-
Support for LogisVert government grants
Do you live in Montréal, Laval, Longueuil, on the North Shore or South Shore and notice frost on your outdoor unit?
Don’t let the problem get worse. Contact AirGreen today for a maintenance call or inspection, and restore your HVAC system’s full efficiency.