Air Conditioning Problems: Not Cooling, Leaking, Smelling Bad or Making Noise
Quick 2026 diagnosis: identify the symptom, apply step-by-step solutions, and discover when it is urgent to call a professional technician. Includes error codes and seasonal prevention.
⚠️ Safety Warning Before starting
Before handling any internal component, disconnect the unit from the electrical supply at the main breaker panel. Never work on the unit while it is plugged in.
If you detect a burning smell, sparks, smoke, or loud metallic noises, immediately turn off the unit at the electrical panel and call a professional. Do not attempt to diagnose electrical problems without proper training.
Important: Interventions on the refrigeration circuit (refrigerant gas) require professional certification and are regulated by environmental regulations. Do not attempt to recharge the gas yourself.
🌳Diagnosis tree: identify your problem in 3 steps
Step 1: What is your unit doing (or not doing)?
Step 2: When does the problem occur?
- 🌞 Only during peak heat hours → Possible overheating or undersizing
- 🌙 Only at night → Possible misconfigured eco mode or thermostat
- 💨 When turning it on for the first time this season → Possible accumulated dirt
- ⚡ After a power outage → Possible electronic failure or need for a reset
Step 3: Have you done recent maintenance?
- ✅ Filters cleaned in the last 30 days → Rule out the most common cause
- ❌ No maintenance since last year → Clean filters BEFORE diagnosing further
🔍 Don't know what's wrong with your AC? Diagnosis in 3 questions
📊Comparison table: Can I fix it myself?
| Problem | Most frequent causes | Difficulty | Urgency | % of cases |
|---|---|---|---|---|
| ❄️ Not cooling | Dirty filters, misconfigured thermostat, obstructed outdoor unit | Easy | Medium | 70% |
| 💧 Leaking water | Clogged drain, broken pan, poorly leveled installation | Easy-Medium | Medium | 60% |
| 🔊 Strange noises | Vibrations, loose parts, worn bearings | Technician | High (if metallic) | 45% |
| 👃 Bad smell | Mold/bacteria in filters, electrical problem (burnt) | Easy (if mold) | Urgent (if burnt) | 35% |
| 🔌 Shutting off on its own | Overheating, sensor failure, voltage problems | Technician | High | 25% |
| 🔢 Error code | Specific failure detected by the system | Technician | Medium-High | 20% |
| ❄️ Lack of gas | Leak in the refrigeration circuit | Technician (Certified) | Medium | 15% |
1My air conditioner is not cooling (but air is coming out)
Problem → Cause → Solution
Direct answer: The most frequent cause (70% of cases) is clogged filters that reduce airflow. Clean or replace the filters, verify that the thermostat is set to "COOL" mode and temperature <26°C, and ensure the outdoor unit is not obstructed. If the problem persists >24 hours after these steps, it could indicate a refrigerant leak or electrical failure.
Steps to diagnose "not cooling" in 5 minutes:
1. Turn off the unit and remove the filters: Lift the front cover (it usually opens upwards or to the sides). Carefully remove the filter meshes.
2. Clean with warm water or a vacuum: Use warm water with mild soap if they are very dirty. Let them dry completely in the shade (direct sunlight can deform the plastic). Never use aggressive detergents.
3. Check the thermostat: "COOL" mode, temperature 3-5°C below the current ambient temperature. If it is digital, check that the batteries are charged.
4. Check the outdoor unit: No leaves, dust, or furniture blocking the grilles. Keep 50cm clear around it.
5. Turn on and wait 15 minutes: If it doesn't improve, consult the full section below.
Cause: Frozen indoor unit (ice on pipes)
Symptoms: You see ice on the copper pipes or on the indoor unit. The air comes out very weak or not at all.
Cause: Very dirty filters, lack of gas, or broken indoor fan.
Solution: Turn off the unit immediately and let it defrost for 4-6 hours. Clean the filters thoroughly. If it freezes again upon restarting in <2 hours, call a technician (possible gas leak or fan failure).
Cause: Lack of refrigerant gas (leak)*
Symptoms: The unit runs but doesn't cool at all, the pipes are not cold to the touch, or you see ice on the service valve.
Important: Gas is NOT a consumable. If it is missing, there is a leak that must be repaired.
Solution (technical level): Do not attempt to recharge the gas yourself. It requires specialized tools (manometers), professional certification, and leak diagnosis. Contact an authorized technician. Approximate cost: 230-600€ (detection + repair + recharge).
2The air conditioner is leaking water from the indoor unit
Problem → Cause → Solution
Direct answer: A small drip at the outdoor drain outlet is normal, as the unit removes moisture from the environment. If there are large puddles or leaks inside the house, it indicates a clogged drain or a damaged pan. Clean the drain with warm water and vinegar; if it persists, call a technician.
Cause: Clogged drain (90% of internal leaks)
Symptoms: Water dripping from the indoor unit, puddles on the floor under the unit, or water coming out of the wall.
Step-by-step solution:
- Locate the drain pipe (it usually comes out of the indoor unit to the outside or a drain)
- Pour 200ml of warm water with white vinegar (3:1 ratio) down the drain
- Wait 15 minutes and check if the water flows freely
- If it is still clogged, use a large syringe or funnel to apply gentle pressure
- Never use aggressive chemicals (bleach, lye) that can damage the pipes
Cause: Cracked or poorly leveled condensate pan
Symptoms: Water does not flow to the drain but accumulates and overflows over the sides.
Solution: Verify that the indoor unit is perfectly leveled (slightly tilted towards the drain). If the pan is broken, stop using the unit and call a technician to replace it. Stagnant water can cause short circuits and mold.
Cause: Excess ambient humidity
Symptoms: Abundant dripping only on very humid days (>80% relative humidity).
Solution: It is normal. Ensure the outdoor drain ends in a suitable place (not over walkways). If the dripping is excessive, consider using a complementary dehumidifier.
Alert: internal puddles, continuous leaks, or water on the floor
3It is making strange noises (humming, squeaking, banging)
Problem → Cause → Solution
Classification of noises and their meaning:
Soft hum / slight vibration: Normal or due to dirty filters. Solution: Clean filters and check mountings.
Metallic squeaks: Worn belts or unlubricated bearings. Solution: Turn off immediately and call a technician.
Dry bangs: Loose internal parts or unbalanced fan. Solution: Turn off and contact a professional.
High-pitched whistle: Irregular refrigerant flow or obstruction. Solution: Requires diagnosis with manometers.
Bubbling: Air or moisture in the refrigeration circuit. Solution: Specialized technician.
Solution for vibrations (easy level):
1) Check that all mounting screws are tightened (without exceeding the recommended torque).
2) Clean the filters (turbulent flow causes vibration).
3) Place an anti-vibration mat under the indoor unit if it is on a rigid surface.
4) Ensure the intake/outlet grilles are free of obstacles.
4It smells like dampness or sewer when turned on
Problem → Cause → Solution
Damp, mold, or "dirty" smell
Cause: Accumulation of condensation in the evaporator + dust = breeding ground for mold and bacteria. Common after periods of inactivity or in very humid environments.
Solution (easy level):
- Clean or replace the filters
- Turn on the unit in "fan" mode (without cooling) for 30-60 minutes to dry the inside
- Use a specific air conditioner deodorizer (avoid generic air fresheners that can damage components)
- If it persists, consider a professional cleaning of the evaporator
Burning, plastic, or chemical smell (EMERGENCY)
Serious cause: Overheating of electrical components, melted wire insulation, or failure in the electronic board. It may indicate a fire risk.
Solution (URGENT): Immediately turn off the unit at the electrical panel. Do not turn it on again. Contact a certified technician for inspection of wiring, connections, and electronic components.
5It shuts off repeatedly on its own
Problem → Cause → Solution
Frequent causes:
- Overheating: Clogged filters or blocked outdoor unit. The safety system shuts off the compressor.
- Temperature sensor failure: Sends incorrect readings to the board.
- Electrical voltage problems: Power surges or loose connections.
- Timer activated: Check that you don't have an automatic shutdown programmed.
- Electronic board failure: Requires professional diagnosis.
Step-by-step solution:
1) Clean the filters thoroughly.
2) Check outdoor ventilation.
3) Wait 30 minutes before restarting.
4) If the problem persists, write down the error code (if it appears) and call a technician.
🔢Common error codes by brand (2026)
Error codes appear on the display (E1, F3, P0, etc.) and indicate specific failures. Each brand has its own table. Here are the most frequent ones excluding Daikin and Mitsubishi:
LG / General
CH01 / E1Defective ambient temperature sensor. Check sensor connections.
LG / General
CH05 / E5Communication problem between indoor and outdoor units. Check wiring.
Samsung
E401Indoor fan failure. Motor blocked or dirty.
Samsung
E416Pressure problem. Possible gas leak or defective expansion valve.
Haier / Carrier
E1High pressure protection. Outdoor unit obstructed or outdoor fan broken.
Haier / Carrier
E4Compressor protection. Overheating or electrical failure.
Panasonic
F11Communication problem. Damaged wiring or loose connectors.
Panasonic
H11Indoor-outdoor communication anomaly. Reset unit and check.
📞When to call an air conditioning technician (very important)
This section is key for your safety, the longevity of the unit, and the validity of the warranty. Not all problems require professional intervention, but ignoring the right signs can turn a simple repair into an expensive one.
You can solve it yourself if...
- The problem disappears after cleaning the filters
- It is a thermostat setting adjustment
- The outdoor unit was temporarily obstructed
- The leak is slight and is solved by cleaning the drain
- The noise was due to vibration and is corrected by adjusting mountings
- Damp smell that disappears after cleaning and ventilating
Call a technician IMMEDIATELY if...
- It smells like burning, plastic, or chemicals
- You hear metallic noises, loud squeaks, or bangs
- There are water leaks inside the house that do not stop
- The unit shuts off repeatedly on its own after cleaning filters
- You see sparks, smoke, or the electrical panel trips when turning it on
- The unit is over 10 years old and shows new failures
- An error code appears that is not resolved with a reset
- You see ice on pipes after cleaning the filters
Tip to save time and money
Before calling, prepare this information for the technician: 1) Model and year of the unit (label on outdoor unit), 2) Exact description of the problem (when it started, frequency), 3) Steps you already tried, 4) Error code (if it appears), 5) Photos or videos of the failure (if it is safe to do so). This speeds up diagnosis and reduces labor costs.
📅Seasonal prevention: avoid problems before they occur
Most failures can be prevented with simple habits. This checklist helps you act before the critical season:
🌸 Spring (pre-summer): preparation
- ☐ Clean or replace indoor filters
- ☐ Check that the outdoor unit is free of leaves, dust, or vegetation
- ☐ Verify that the drain pipe is not bent or disconnected
- ☐ Test the unit in fan mode for 15 minutes to detect new noises
- ☐ Update firmware if your unit is smart (via manufacturer's app)
- ☐ Schedule annual professional check-up (evaporator cleaning, gas check)
☀️ Summer (intensive use): express maintenance
- ☐ Clean filters every 4-6 weeks
- ☐ Do not block intake/outlet grilles with furniture or curtains
- ☐ Keep temperature between 24-26°C to avoid overexertion
- ☐ Close doors of unused rooms to optimize airflow
- ☐ Pour water with vinegar down the drain monthly
- ☐ Listen for new noises when turning it on each morning
🍂 Autumn (post-summer): safe shutdown
- ☐ Clean filters before storing the unit (if portable)
- ☐ Leave the unit in fan mode for 1 hour to dry the internal evaporator
- ☐ Cover the outdoor unit with a protective cover if you live in an area with a lot of dust/leaves
- ☐ Note any minor failures to mention them at the next professional check-up
- ☐ Disconnect completely if you will not use it in winter (standby savings)
❄️ Winter (heat pump): if you use heating
- ☐ Check that the outdoor drainage does not freeze (cold climates)
- ☐ Clean filters with the same frequency as in summer
- ☐ Do not turn off the unit completely if you use it occasionally
- ☐ "Standby" mode consumes less than a cold start
- ☐ Check that the outdoor grilles are not blocked by snow/ice
❓Frequently asked questions about air conditioning problems
Common air conditioning problems —not cooling, leaking water, making noise, smelling bad, or shutting off on its own— have, in many cases, accessible solutions that you can apply with basic tools and by following clear instructions. The key is in the orderly diagnosis: symptom → cause → solution → urgency level.
Remember the three fundamental rules: 1) Clean the filters regularly (it is the cause of 70% of reported failures), 2) Never ignore burning smells or metallic noises (warning signs that require immediate action), and 3) When in doubt, call a professional (the safety and warranty of your unit are worth more than an amateur repair attempt).
With basic prevention and early diagnosis, you can extend the lifespan of your air conditioner, reduce energy consumption, and enjoy reliable thermal comfort season after season. For professional assistance, look for certified technicians with experience in your specific brand and model.
