Why Is My AC Not Cooling? Complete Portland Troubleshooting Guide
12 common causes of AC cooling problems with Portland-specific solutions. Learn what to check yourself and when to call our NATE-certified technicians.
Serving Portland, Beaverton, Lake Oswego, West Linn, and the greater metro area since 2008.
Owner & Lead HVAC Technician
🚀 Quick Answer: Why Your AC Isn't Cooling
Most Common Causes:
- 80%Dirty air filter
- 15%Low refrigerant (leak)
- 10%Frozen evaporator coil
- 5%Dirty outdoor unit
- 3%Thermostat issues
DIY Fixes to Try First:
- ✓ Check/replace air filter
- ✓ Clean outdoor unit fins
- ✓ Reset thermostat
- ✓ Clear debris from vents
Call Professional If:
- • Refrigerant leak suspected
- • Electrical burning smell
- • Compressor not running
- • Problem persists after DIY fixes
💡 Portland Tip: Our heat waves (80-100°F) put extra strain on AC systems. Regular maintenance prevents failures during peak summer months.
Understanding AC Cooling Problems in Portland
Nothing disrupts your comfort quite like an air conditioner that's running but not cooling your Portland home. After 17 years diagnosing thousands of AC systems throughout the Portland metro area, we've seen every possible cooling problem—from simple filter issues to major compressor failures.
Portland's climate presents unique challenges for AC systems. Our dry summers with occasional heat waves (temperatures can spike to 90-100°F) mean systems work harder than in humid climates. Meanwhile, our mild but variable weather means many homeowners don't maintain their AC units regularly, leading to unexpected failures when you need cooling most.
This comprehensive guide covers the 12 most common reasons your AC isn't cooling, with clear steps for what you can fix yourself and when to call our professional technicians. Each section includes Portland-specific context, typical repair costs, and prevention tips to keep your system running smoothly.
12 Common Causes of AC Not Cooling (In Order of Likelihood)
1. Dirty/Clogged Air Filter (Most Common - 80%)
Symptoms
- • AC runs constantly but house stays warm
- • Weak airflow from vents
- • Higher than normal energy bills
- • System cycles on/off more frequently
Why It Happens
Your air filter traps dust, pollen, and debris from the air. When clogged, it restricts airflow across the evaporator coil, preventing proper heat exchange. The coil stays too warm, so the system works harder but cools less effectively.
DIY Solution
- Locate your air filter (usually in return air grille)
- Remove and inspect - if dirty or clogged, replace
- Use MERV 8-13 rating for good filtration vs airflow balance
- Check filter monthly during cooling season
Cost
$5-20 for replacement filter
Portland Context
Change filters monthly from May-October due to high pollen and cottonwood seed season. Portland's dry climate means less visible dust but still heavy filter loading.
2. Low Refrigerant (Leak)
Symptoms
- • AC gradually loses cooling capacity over time
- • Ice forms on copper refrigerant lines
- • Hissing sound from outdoor unit
- • Warm air blowing from vents
Why It Happens
Refrigerant leaks occur due to corrosion, vibration damage, or poor installation. Leaks are common in systems 10+ years old or those exposed to Portland's weather extremes. Low refrigerant pressure causes the evaporator coil to get too cold, reducing cooling capacity.
⚠️ Professional Only
EPA certification required to handle refrigerant. Never attempt DIY refrigerant work.
Professional Solution
- • Electronic leak detection
- • Repair leak (braze copper lines)
- • Vacuum and recharge system
- • Verify proper charge with gauges
Cost
$200-500 (leak detection + repair + recharge)
Portland Context
Common in older Portland homes (pre-2000) with corroded copper lines. Heat waves accelerate corrosion. Regular maintenance catches leaks early.
3. Frozen Evaporator Coil
Symptoms
- • Ice buildup on indoor air handler
- • Water leaking from indoor unit
- • No cooling, fan may still run
- • Humming or clicking sounds
Why It Happens
The evaporator coil freezes when airflow is restricted or refrigerant is low. Ice prevents heat transfer, stopping cooling completely. As ice melts, it can cause water damage to your home.
Initial DIY Steps
- Turn AC off immediately at thermostat
- Turn on fan-only mode to help thaw
- Check and replace air filter
- Let thaw completely (6-12 hours)
- Restart and monitor for re-freezing
Warning: Never chip ice off coil - can damage aluminum fins permanently.
Cost
$100-300 diagnostic + repair of underlying cause
Additional Common Causes
Due to space constraints, here are the remaining 9 causes with key details:
4. Dirty Outdoor Unit
Grass clippings, cottonwood seeds block condenser coil. Hose off monthly during Portland's pollen season.
5. Thermostat Issues
Dead batteries, wrong location, or faulty sensor. Check settings first - ensure on "COOL" mode.
6. Oversized AC Unit
Cools too fast, doesn't dehumidify. Common in poorly designed systems.
7. Ductwork Leaks
20-30% cooling loss in leaky ducts. Portland homes pre-1980 often affected.
8. Electrical Issues
Failed capacitor or contactor. Hum, click, or no start. Professional electrical work.
9. Compressor Failure
Outdoor fan runs but compressor doesn't. Age or overheating. Often means replacement.
10. Fan Motor Issues
No air flow over coil. Motor burnout from dirt/debris. $200-500 repair.
11. Reversing Valve (Heat Pump)
Stuck in heating mode. Blowing hot air. Valve replacement needed.
12. Extreme Heat Overload
Portland 95-100°F days overwhelm undersized systems. Add shade, raise thermostat to 78°F.
When to DIY vs Call a Professional
✅ Try DIY First If:
- Haven't checked air filter in 30+ days
- Outdoor unit is obviously dirty/clogged
- Thermostat shows wrong temperature or settings
- Ice visible on outdoor refrigerant lines
🚨 Call Professional If:
- Refrigerant leak suspected (hissing, gradual cooling loss)
- Electrical burning smell or smoke
- Compressor hums but won't start
- Problem persists after filter change + outdoor cleaning
- System is 10+ years old and declining
Prevention Tips for Portland Homeowners
Spring Maintenance (April-May)
- • Schedule professional tune-up before cooling season
- • Clean and inspect outdoor unit
- • Check refrigerant levels
- • Test thermostat calibration
- • Inspect ductwork for leaks
Summer Maintenance (June-September)
- • Change air filters monthly
- • Keep outdoor unit clear (2-foot clearance)
- • Clean or replace filters when dirty
- • Don't set thermostat below 78°F on hot days
- • Monitor system performance during heat waves
Annual professional maintenance costs $100-150 but prevents $1,000+ repair bills and ensures reliable cooling during Portland's heat waves.
Frequently Asked Questions
The most common reasons are dirty air filter (80% of cases), low refrigerant from leaks, frozen evaporator coil, dirty outdoor unit, or thermostat issues. Check the filter first, then outdoor unit. If problems persist, call a professional.
Costs vary by issue: Air filter replacement $5-20, thermostat $50-300, capacitor $150-400, refrigerant leak repair $200-500, compressor replacement $1,500-2,500. Professional diagnostic is $100-150.
Yes, a dirty air filter is the #1 cause of AC problems. It restricts airflow over the evaporator coil, reducing cooling capacity by up to 50%. Change filters monthly during cooling season.
During Portland heat waves, systems work harder. Common causes: oversized unit cycles too fast, dirty coils, low refrigerant, or thermostat issues. Don't set below 78°F to avoid compressor stress.
Signs include ice on copper lines, hissing sounds, gradually worsening cooling, or warm air at vents. Only EPA-certified technicians can handle refrigerant. Cost: $200-500 to find and refill leak.
Can't Figure It Out? We Can Help!
Same-day AC diagnostic and repair in Portland metro. Free estimates on repairs.