Why does my air conditioner run constantly?
An AC that never shuts off drives up your hydro bill and wears out components faster. But before assuming a breakdown, it helps to know that some extended running is normal during a Metro Vancouver heatwave.
The key question is context. If your AC runs continuously when it’s 35C outside, it may simply be keeping pace with demand. If it runs non-stop on a mild 24C day and still can’t hit your setpoint, something is reducing its efficiency.
At HeatLand, serving Metro Vancouver and the Fraser Valley since 1999, we help homeowners distinguish normal hard-working operation from the airflow, refrigerant, and sizing issues that keep a system running when it shouldn’t.
When Constant Running Is Actually Normal
During an extreme heat event, an appropriately sized AC may run almost continuously and that’s expected, not a fault. Air conditioners are typically sized to keep your home comfortable at a design temperature, and when outdoor temperatures exceed that, the unit simply can’t cycle off because it’s working at capacity. In these conditions, constant running is the system doing its job. You’ll know it’s coping if the indoor temperature stays reasonably close to your setpoint, even if it drifts a degree or two. Problems arise when the outdoor temperature is moderate but the AC still won’t shut off. That points to lost efficiency somewhere in the system. Setting your thermostat unrealistically low (say, 18C on a 32C day) also forces near-constant running because the unit chases a target it can barely reach. A more moderate setpoint reduces runtime and energy use while keeping the home comfortable. If normal-weather constant running is your concern, read on.
Airflow and Dirt: The Efficiency Killers
The most common fixable cause of constant running is restricted airflow or dirty components. A clogged air filter forces the system to work harder and longer to move cooled air, so it runs extended cycles. Replace filters regularly, roughly every one to three months depending on pets and pollen. A dirty evaporator coil (indoors) or condenser coil (outdoors) has the same effect: the system can’t transfer heat efficiently, so it runs and runs. The outdoor condenser is especially prone to collecting grass, cottonwood fluff, and dirt in Fraser Valley yards; rinse the fins gently with a hose (power off) and keep two feet of clearance. Leaky or undersized ductwork also causes constant running by losing cooled air into attics or crawlspaces before it reaches your rooms. Poor insulation and air-sealing let heat pour back in, making the AC chase a moving target. Addressing filters, coils, ducts, and insulation often restores normal cycling and cuts your energy bill noticeably.
Sizing, Refrigerant, and Mechanical Causes
If your AC runs constantly even after cleaning and the weather is moderate, deeper causes may be at play. Low refrigerant from a leak reduces cooling capacity, so the system runs endlessly trying to reach the setpoint, often paired with warm vents and higher bills. Refrigerant work is regulated and requires a licensed technician. An undersized unit, one too small for your home’s square footage or heat load, will run non-stop by design; this is common after additions or when a system was under-specified at install. Conversely, worn compressor components can reduce output over time. A failing thermostat that misreads temperature can also command endless running. Safety note: constant running that trips breakers, produces burning smells, or is accompanied by electrical buzzing should prompt you to shut the system off and call a professional immediately. HeatLand’s licensed technicians perform proper load calculations, leak detection, and repairs across all major brands, so your AC cools efficiently instead of running itself into the ground.
Quick Checklist
- Set a realistic thermostat target for the weather
- Replace the air filter if dirty
- Clean the outdoor condenser coil and clear debris
- Check for obvious duct leaks in accessible areas
- Note if constant running only happens on mild days
- Watch for warm vents signalling low refrigerant
| Cause | Runs Constantly Because | Fix |
|---|---|---|
| Extreme heat | Working at full capacity | Normal; moderate the setpoint |
| Dirty filter or coil | Reduced heat transfer | Clean or replace |
| Low refrigerant | Can’t reach setpoint | Licensed technician |
| Undersized unit | Too small for the load | Professional load calc |
| Leaky ductwork | Cooled air lost en route | Seal or repair ducts |
Frequently Asked Questions
Is it bad for my AC to run all day?
During extreme heat, continuous running is normal and not harmful if the unit keeps pace. On mild days, constant running signals lost efficiency from dirty filters, low refrigerant, or duct leaks. Prolonged unnecessary running raises energy bills and accelerates wear, so it’s worth diagnosing.
Could my AC be too small for my house?
Yes. An undersized system runs non-stop trying to meet demand it can’t satisfy, especially after home additions or if it was under-specified at install. A licensed technician can perform a proper load calculation to confirm whether your unit matches your home’s cooling needs.
Will a dirty filter make my AC run constantly?
It can. A clogged filter restricts airflow, so the system works harder and longer to move cooled air and may even freeze the coil. Replacing the filter every one to three months is a cheap, easy step that often restores normal cycling and lowers runtime.
When should I call a technician about constant running?
Call a professional if your AC runs non-stop on mild days, produces warm air, trips breakers, or you notice burning smells or electrical buzzing. These point to refrigerant, sizing, or mechanical faults. HeatLand serves Metro Vancouver and the Fraser Valley with licensed diagnostics.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.