🔧 AC Not Cooling? Complete Guide to Fix Compressor, Gas & Filter Problems
Problem Overview
Your AC turns on, fan runs, and you hear sounds, but the air isn't cold enough or the room won't cool down. This frustrating issue has several causes: compressor failure, refrigerant gas leaks, dirty air filters blocking airflow, thermostat problems, or outdoor unit issues. This comprehensive guide helps you diagnose and fix the exact cause.
Safety First
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Gas leak hazard: Never attempt to handle refrigerant yourself. Gas leaks require professional technicians with proper equipment and certification. Inhaling refrigerant can be harmful.
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Turn off power before cleaning: Always switch off AC at the circuit breaker before opening panels or cleaning internal components to prevent electric shock.
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Don't touch outdoor unit internals: The outdoor unit contains high-voltage capacitors and compressor. Only qualified technicians should open it. External cleaning is safe.
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Height safety: Use stable ladder and helper when cleaning outdoor units installed at height. Never lean out of windows to clean external units.
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Warranty preservation: Opening sealed components or attempting refrigerant work will void warranty. Check warranty status before DIY troubleshooting beyond basic cleaning.
🔍 Quick Checks ⏱️ 3-5 minutes
1 Check Temperature Setting
Verify AC is set to cooling mode (not fan/dry), temperature is set to 18-20°C, and fan speed is on high. Common oversight that prevents cooling.
2 Inspect Air Filter
Open indoor unit front panel and check filter. If visibly dusty/clogged, this blocks airflow causing weak cooling. Clean or replace immediately.
3 Listen to Outdoor Unit
Go outside and listen. Is compressor running (consistent humming/vibration)? Or just fan spinning? If only fan runs, compressor issue is likely.
4 Check Outdoor Unit Airflow
Feel air coming from outdoor unit—should be hot. Check for obstructions, plants, or debris blocking coils. Clear 2-foot space all around.
5 Measure Temperature Difference
Use thermometer: measure room temperature vs air from AC vent. Difference should be 8-12°C. Less than 5°C indicates cooling problem.
6 Look for Ice Formation
Check indoor unit coils (behind filter). Ice buildup indicates airflow problem or low refrigerant. Turn off AC to defrost if iced up.
💡 Common Causes → Solutions
Problem
Dirty/clogged air filters blocking airflow
Solution
Remove filters, wash with mild detergent and water, dry completely, reinstall. Clean every 2 weeks in dusty areas. Instant cooling improvement.
Problem
Low refrigerant gas due to leak or improper installation
Solution
Call technician for leak detection, repair, vacuum, and gas refill. Cost: ₹2,000-₹5,000. Requires specialized equipment and certification—never DIY.
Problem
Compressor not running (capacitor failure, relay issue)
Solution
Technician replaces faulty capacitor (₹300-₹800) or compressor relay (₹500-₹1,500). If compressor burned out, replacement costs ₹8,000-₹20,000.
Problem
Dirty evaporator or condenser coils reducing efficiency
Solution
Professional deep cleaning service (₹800-₹2,000). Outdoor coil can be gently cleaned with water spray (power off). Indoor coil requires technician with coil cleaner.
Problem
Undersized AC for room (wrong tonnage calculation)
Solution
Formula: 1 ton per 120 sq.ft (+ 0.5 ton for top floor/sun-facing). If severely undersized, consider upgrading AC. Interim: seal doors/windows, use curtains.
Problem
Faulty thermostat/temperature sensor reading incorrectly
Solution
Reset AC to factory settings. If issue persists, sensor replacement by technician (₹800-₹2,500). Sensor tells AC when to turn compressor on/off.
Problem
Blocked or kinked copper refrigerant lines
Solution
Inspect visible copper pipes between units. Look for sharp bends, crimps, or pressure from furniture. Technician can straighten or reroute if needed.
Problem
Excessive heat load (too many people, appliances, sunlight)
Solution
Use blackout curtains for sun-facing windows, minimize door opening, turn off heat-generating appliances, run exhaust fans before AC starts. Pre-cool room before occupancy.
🛠️ Step-by-Step DIY Troubleshooting
Clean Air Filters Thoroughly
• Turn off AC and open front panel/cover of indoor unit
• Remove mesh filters (usually slide out or have tabs to lift)
• Wash with mild detergent and lukewarm water, scrub gently with soft brush
• Rinse thoroughly, shake off excess water, air dry completely (2-3 hours)
• Never reinstall wet filters—can cause mold and electrical issues
• Clean filters every 2 weeks in dusty areas, monthly in clean environments
Verify Compressor Operation
• Set AC to coolest setting (16-18°C) and maximum fan speed
• Wait 5 minutes for compressor to start (initial delay is normal)
• Go to outdoor unit—you should hear steady humming and feel vibration
• Fan should spin and blow HOT air (heat being expelled from room)
• If fan spins but no compressor sound/vibration = compressor issue
• If nothing happens = electrical or control board problem
Clean Outdoor Unit Condenser Coils
• Turn OFF AC circuit breaker for safety
• Remove any debris, leaves, or obstructions around outdoor unit
• Gently spray water through condenser fins (from inside-out direction)
• Use garden hose with moderate pressure—don't bend delicate fins
• Clear 2 feet of space on all sides for proper airflow
• For heavy dirt, call technician for chemical coil cleaning
Check for Ice Buildup on Indoor Coils
• Remove filters and look at metal coils behind them (evaporator coils)
• If coils are iced over, this blocks cooling and indicates a problem
• Turn AC off and let ice melt completely (2-4 hours, use towels for dripping water)
• Ice causes: dirty filters (most common), low refrigerant, fan problems, or blocked airflow
• After defrosting, clean filters and run AC—if ice returns, call technician
Inspect for Refrigerant Gas Leaks
Signs of gas leak:
• Hissing sound from refrigerant lines or joints
• Oil stains around copper pipe connections
• Ice formation on outdoor unit (unusual)
• AC cools briefly then stops, repeating cycle
• Compressor runs but absolutely no cooling
If leak suspected, call technician immediately—do not run AC
Verify Thermostat/Temperature Settings
• Check AC is in COOL mode (not fan, dry, or auto)
• Set temperature to minimum (16-18°C) to test maximum cooling
• Ensure timer is not set accidentally
• Try resetting AC to factory defaults (check manual for procedure)
• Some ACs have eco/power-saving modes limiting compressor—disable for testing
• If digital display shows wrong room temp, sensor may be faulty
Measure Cooling Performance (Temperature Test)
• Use accurate thermometer (digital preferred)
• Measure room ambient temperature first
• Hold thermometer near AC air outlet (not in direct stream)
• Temperature difference (delta-T) should be 8-12°C for healthy AC
• Example: Room at 32°C, AC air at 22°C = 10°C delta (good)
• Less than 5°C difference = cooling problem confirmed
• More than 15°C difference may indicate oversized AC or sensor issue
Reduce Room Heat Load
• Install blackout curtains or reflective film on sun-facing windows
• Seal gaps around doors and windows (weatherstripping)
• Minimize door opening during peak heat hours
• Turn off unnecessary heat sources (lights, ovens, other appliances)
• Use ceiling fan WITH AC (helps circulation, not instead of AC)
• Close vents in unused rooms to concentrate cooling
• Avoid having many people in room during hottest hours
Check Tonnage vs Room Size Match
Tonnage calculation formula:
• Base: 1 ton per 120 sq.ft for ground/middle floors
• Top floor or sun-facing: 1 ton per 100 sq.ft
• Add 0.5 ton if kitchen or many occupants (5+)
• Example: 150 sq.ft room, ground floor = 1.5 ton AC
• Example: 120 sq.ft room, top floor = 1.5 ton AC
If AC is severely undersized, it will run constantly without cooling adequately
Final Diagnosis: Professional Assessment Needed
If all above steps completed and AC still not cooling properly:
• Low refrigerant requiring leak detection and refill (₹2,000-₹5,000)
• Compressor weak or failing (₹8,000-₹20,000 replacement)
• Faulty expansion valve or capillary tube blockage
• Internal coil freeze due to restricted airflow
• PCB or sensor malfunction affecting compressor control
Professional diagnosis with pressure gauges and multimeter required
📞 When to Call a Professional
⚡ Refrigerant & Gas Issues
- • Suspected refrigerant leak (hissing, oil stains)
- • Ice formation on outdoor unit or copper pipes
- • AC cools for 5-10 minutes then stops repeatedly
- • Compressor runs constantly but no cooling
- • Recent installation with poor cooling from day one
🔧 Mechanical & Component Failures
- • Compressor not starting (no sound, no vibration)
- • Outdoor fan not spinning despite power
- • Burning smell from indoor or outdoor unit
- • Unusual loud grinding, clicking, or banging noises
- • Ice keeps reforming after defrosting despite clean filters
💰 Expected Repair Costs (2025 India)
Capacitor Replacement: ₹300-₹800
Coil Deep Cleaning: ₹800-₹2,000
Fan Motor Replacement: ₹2,000-₹4,500
Expansion Valve: ₹1,500-₹3,500
PCB Repair/Replace: ₹2,500-₹7,000
General Service: ₹500-₹1,500
🔍 Questions to Ask Technician
- • What is the exact problem diagnosis? (Ask for pressure readings, temperature measurements)
- • Is refrigerant low? If yes, where is the leak? (Leak must be repaired before refilling)
- • What is current gas pressure? (Should be 65-70 PSI for most residential ACs)
- • Is warranty still valid? (For new ACs, insist on authorized service center)
- • Can I see the problem? (Ask to see dirty coils, faulty component, etc.)
- • What's total cost breakdown? (Parts + labor + gas separately listed)
📊 Cooling Performance Standards
| Parameter | Healthy AC | Needs Attention | Serious Problem |
|---|---|---|---|
| Temperature Delta (Room - AC Air) | 8-12°C | 5-7°C | < 5°C |
| Time to Cool Room (35°C to 26°C) | 20-30 min | 40-60 min | > 60 min |
| Compressor Duty Cycle (ON time) | 60-80% | 90-100% | 100% continuous |
| Outdoor Air Temperature (expelled heat) | 10-15°C above ambient | 5-10°C above ambient | Same as ambient |
| Filter Cleaning Frequency (Normal Use) | Every 2-4 weeks | Weekly (dusty area) | Never cleaned |
| Ice/Frost on Indoor Coils | None | Light frost edges | Heavy ice buildup |
🛡️ Preventive Care & Maintenance
Every 2 Weeks
Clean indoor air filters, check for unusual sounds, inspect outdoor unit for debris, test cooling performance briefly
Twice Yearly (Pre-Summer/Winter)
Professional deep cleaning, gas pressure check, coil inspection, drainage check, electrical connections tightening, capacitor testing
Warning Signs
Gradual cooling decrease, longer time to cool room, ice on pipes, unusual noises, higher electricity bills, water leaks
💡 Essential Prevention Tips:
- • Regular filter cleaning: Single most important maintenance task—prevents 70% of cooling issues
- • Annual coil cleaning: Professional chemical cleaning of indoor/outdoor coils maintains 90%+ efficiency
- • Proper room sealing: Fix door/window gaps—saves up to 30% cooling capacity waste
- • Adequate clearance: Maintain 2 feet clear space around outdoor unit for optimal heat rejection
- • Voltage stabilizer: Protects compressor from voltage fluctuations extending lifespan by 3-5 years
- • Correct tonnage: Ensure AC matches room size—undersized AC runs constantly, oversized AC short-cycles
- • Use thermostat wisely: Set realistic temp (24-26°C), avoid frequent on/off, use timer for efficiency
- • Professional service: Annual checkup catches small issues before becoming expensive repairs
📋 Annual Maintenance Checklist (For Technician)
✓ Deep clean evaporator coils
✓ Check and clean drain pan/pipe
✓ Test blower motor and fan
✓ Inspect electrical connections
✓ Clean filters or replace if damaged
✓ Clean condenser coils thoroughly
✓ Check refrigerant pressure (65-70 PSI)
✓ Test compressor and fan motor
✓ Inspect capacitor condition
✓ Tighten all electrical connections
❓ Frequently Asked Questions
Q1: AC was cooling fine last week, suddenly weak cooling. What changed?
Most common culprit: dirty filters accumulated dust rapidly during peak summer. Clean filters first. Other sudden causes: refrigerant leak started, compressor capacitor weakening, outdoor coils blocked by debris/pollen. If filter cleaning doesn't help immediately, call technician.
Q2: How do I know if AC gas is low without calling technician?
Signs of low refrigerant: (1) AC runs but barely cools, (2) Ice formation on indoor copper pipes or coils, (3) Hissing sound from refrigerant lines, (4) Compressor runs continuously but no cooling, (5) Outdoor air not significantly hotter than ambient. Definitive diagnosis requires pressure gauge—call technician.
Q3: Can I refill AC gas myself to save money?
Absolutely NOT. Refrigerant handling requires: (1) EPA certification, (2) Vacuum pump to remove air/moisture, (3) Pressure gauges to measure exact amount, (4) Leak detection and repair first, (5) Proper gas type (R32/R410A/R22). DIY gas filling damages AC, creates safety hazards, and is illegal. Professional service costs ₹2,000-₹5,000—much less than replacing damaged compressor (₹15,000+).
Q4: AC cooling fine at night but weak during peak afternoon. Normal?
Partially normal IF temperature difference maintained. During peak heat (40°C+), AC works harder to maintain set temperature. If AC brings room from 40°C to 28-30°C but no cooler, it may be: (1) Undersized for heat load, (2) Poor room insulation, (3) Direct sunlight through windows, (4) Dirty coils reducing efficiency. Install blackout curtains, clean filters, check tonnage adequacy.
Q5: Outdoor unit fan spinning but compressor not running. What's wrong?
Fan runs on separate motor from compressor. If compressor not starting: (1) Faulty capacitor (most common, ₹300-₹800 fix), (2) Compressor overload protection triggered (wait 30 min, try again), (3) Low voltage preventing startup, (4) Failed relay or contactor, (5) Compressor seized/failed (expensive). Call technician for diagnosis—don't keep trying to start repeatedly.
Q6: How often should AC gas be refilled? Technician says every year.
MYTH: AC is sealed system—gas should NEVER need refilling if no leak. If technician suggests annual gas refill, there's a leak that must be repaired. Proper approach: (1) Find and repair leak, (2) Vacuum system to remove air, (3) Refill gas once to correct pressure, (4) Should last 7-10 years. Annual refills indicate leak being ignored—will damage compressor eventually.
Q7: Ice forming on copper pipes outside indoor unit. What causes this?
Ice on refrigerant pipes indicates: (1) Restricted airflow (dirty filters #1 cause—clean immediately), (2) Low refrigerant charge causing excessive cooling at evaporator, (3) Faulty expansion valve, (4) Blower fan running slow. Turn AC off to defrost, clean filters thoroughly, ensure proper airflow. If ice returns after filter cleaning, call technician for refrigerant pressure check.
Q8: New AC not cooling properly from day one. What should I do?
Installation issue—call installer immediately under warranty. Common problems: (1) Insufficient refrigerant charge, (2) Air in refrigerant lines (improper vacuuming), (3) Wrong tonnage for room size, (4) Kinked refrigerant pipes, (5) Outdoor unit not level. Don't accept "wait a few days" excuse—new AC should cool excellently from day one. Insist on proper diagnosis and correction.
Q9: Is it better to run AC continuously or turn on/off multiple times?
Continuous running is more efficient and better for compressor. Frequent on/off cycles: (1) Consume more power during startup surge, (2) Wear compressor faster, (3) Create temperature fluctuations. Better approach: Set comfortable temp (24-26°C) and let AC maintain it. Use timer to turn off when sleeping or away. Modern inverter ACs designed for continuous operation adjust compressor speed for efficiency.
Q10: AC cooling but room feels humid/uncomfortable. Why?
AC should dehumidify while cooling. Humidity issues indicate: (1) Oversized AC short-cycling (cools fast but doesn't dehumidify), (2) Dry mode needed in monsoon instead of cool mode, (3) Dirty evaporator coils reducing moisture removal, (4) Drain pipe blocked causing water recirculation, (5) Poor room ventilation. Try dry mode, check drain flow, clean coils. If persists, AC may be oversized for room—runs too briefly to dehumidify properly.
⚠️ Disclaimer: This troubleshooting guide is for informational purposes only. Refrigerant handling, compressor repairs, and electrical work require certified professionals. Never attempt to handle refrigerant gas yourself—it's illegal and dangerous. If you're unsure about any step, or if the AC is under warranty, contact authorized service centers. Incorrect repairs can cause equipment damage, personal injury, environmental harm, or void warranty. When in doubt, call a professional technician.
Important Safety Reminder
If you're not comfortable with any step, or if the problem persists after trying these solutions, please contact a qualified technician. Safety should always be your first priority when dealing with electrical appliances.
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