AC Troubleshooting Wizard Calculator

AC not working? Diagnose common problems step-by-step and find out whether it’s a quick DIY
fix or needs a professional technician.
🩺 Symptom Diagnosis
🔧 DIY vs Pro Guidance
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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. Before spending $100+ on a service call, work through the basic checks below — 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. 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.
🧊 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.
❄️ 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.

When to Call a Professional Immediately

Some AC issues are beyond DIY and require a licensed HVAC technician. 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, 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.

Frequently Asked Questions

Why is my AC running but not cooling my home?

The most common causes are: a dirty air filter restricting airflow, low refrigerant due to a leak, a frozen evaporator coil, a dirty condenser coil blocking heat rejection, or an oversized AC that short-cycles. Start by replacing your air filter, cleaning visible components, and checking that your thermostat is set correctly. If the problem persists, a technician should test refrigerant levels and check for coil damage.

This is called short-cycling and has several causes: the most common is an oversized AC that cools the space too quickly before removing humidity; dirty evaporator coils causing high-pressure shutoffs; low refrigerant; or a malfunctioning thermostat. Short-cycling wastes electricity, reduces dehumidification, and stresses the compressor. Check your air filter first, then call a technician if it continues.

Signs of low refrigerant include: the AC blows air but it’s not very cold, ice forms on the refrigerant lines or evaporator coil, there’s a hissing or bubbling sound near the lines, and your electricity bill has increased. Only a certified technician can check and add refrigerant — it’s regulated in Canada. Remember: a properly sealed AC should never need refrigerant top-ups. Low refrigerant always means there’s a leak.

Annual AC tune-ups, ideally in April or May before cooling season, are recommended by all major HVAC manufacturers and are required to maintain most equipment warranties. A professional tune-up includes coil cleaning, refrigerant check, electrical connection inspection, capacitor testing, and efficiency measurement — and typically costs $100–$200.

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