AC Troubleshooting Wizard Calculator

This free AC troubleshooting tool asks a few quick questions about your symptoms,
then tells you whether your air conditioner needs a simple DIY fix or a professional technician.
🩺 Symptom Diagnosis
🔧 DIY vs Pro Guidance
⚡ Instant Results
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AC Troubleshooting Wizard
Which AC issue are you having? Answer a few quick questions to help identify the most likely cause of your air conditioner problem and what to do next.
When you check your thermostat, what do you notice?
What sound do you hear from your AC unit?
How is the airflow from your vents?
When did you last have professional maintenance?
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AC Troubleshooting Results
Most Likely Cause
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Common AC Problems & Solutions in Canada

Most AC problems are caused by a handful of common issues see our full breakdown of common air conditioner problems for more detail. Before spending $100+ on a service call, work through the basic checks below see our breakdown of repair vs. replace costs. many Canadian homeowners solve their cooling problems without a technician.
SymptomLikely CauseFirst CheckDIY or Pro?
AC blowing warm airLow refrigerant, dirty coils, thermostatThermostat setting, filterPro for refrigerant
AC won’t turn onTripped breaker, bad capacitor, thermostatBreaker panel, thermostat✓ DIY first
AC short-cyclingOversized unit, dirty filter, refrigerantReplace air filter✓ DIY first
Water leaking from ACClogged condensate drain, frozen coilClear drain line✓ DIY possible
Outdoor unit not runningCapacitor, contactor, refrigerantCheck breaker, listen for hum⚠ Usually pro
Loud banging/rattlingLoose parts, debris in fan, failing motorTurn off, inspect visually⚠ Often pro
AC icing upLow refrigerant, dirty filter, low airflowReplace filter, turn off, let thaw✓ DIY first
High electricity billLow SEER2, dirty coils, refrigerantClean filters, check thermostat✓ DIY first

Before You Call a Technician — Check These First

🌡️ Check Thermostat
Make sure the thermostat is set to COOL (not Heat or Fan-only), the temperature is set below room temperature, and the batteries aren’t dead. Also check if it’s in AUTO fan mode.
🔌 Check the Breaker
AC units have a dedicated circuit breaker — if resetting it doesn’t work, see our guide on AC is not turning on. Find it in your electrical panel and check if it has tripped. Reset it by switching fully OFF then back ON. A repeatedly tripping breaker means a professional is needed.
🗂️ Replace the Air Filter
A completely blocked air filter is the #1 cause of AC icing, poor cooling, and short-cycling. If you can’t see light through your filter, replace it immediately — this takes under 5 minutes.
see signs your AC needs repair.
🧊 Clear the Drain Line
A clogged condensate drain causes water to back up and leak from your indoor unit. Pour a cup of diluted bleach or vinegar into the drain pan access point to clear algae buildup.
🌿 Clear the Outdoor Unit
Make sure your outdoor condenser unit has at least 2 feet of clearance on all sides. Remove grass, leaves, or debris from around and on top of the unit. Gently rinse the coil fins with a hose.
check our air conditioner maintenance tips for the full seasonal checklist.
❄️ Let Iced Coils Thaw
If your indoor or outdoor unit has ice on it, turn the AC to Fan-Only mode (not cooling) for 2–4 hours to let it thaw completely before restarting. Running a frozen AC risks compressor damage.
our spring AC maintenance checklist can help you prevent this next season.

When to Call a Professional Immediately

Some AC issues are beyond DIY and require a licensed HVAC technician certified through an HRAI-recognized program. Call a pro right away if you experience: the circuit breaker keeps tripping after reset, you notice a burning smell from any component, the outdoor unit hums but the fan won’t spin, your AC is more than 15 years old and stops cooling entirely (see our guide on when to replace your AC), or you suspect a refrigerant leak (hissing sound, bubbling refrigerant lines, persistently frozen coils despite changing the filter).

AC Error Codes

Modern AC systems — especially ductless mini-splits — display error codes on the indoor unit’s display or via LED flash patterns. Our troubleshooting wizard decodes error codes for major Canadian brands including Lennox, Carrier, Trane, Daikin, Mitsubishi, Fujitsu, and LG. Enter your error code in the wizard to get a specific diagnosis and estimated repair cost.

Common Questions About AC Troubleshooting

Why is my AC running but not cooling my home?

Your AC is likely blowing air but not cooling due to a dirty filter, low refrigerant, a frozen coil, or a dirty condenser coil start by replacing the filter and checking the thermostat setting. AC running but not cooling

This is short-cycling, usually caused by an oversized AC, dirty coils, low refrigerant, or a faulty thermostat, and it wastes electricity, reduces dehumidification, and stresses the compressor. learn how to avoid this in our central air conditioner buying guide.

Signs of low refrigerant include weak cooling, ice on the lines, a hissing sound, and rising bills — but only a licensed technician can legally check and add refrigerant in Canada.

Manufacturers recommend an annual AC tune-up each spring which helps protect your system’s SEER efficiency rating, typically costs $100–$200, and is required to keep most warranties valid

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