Identifying the right cause helps you save on repair costs and avoid serious damage — from dust and low refrigerant to a failing compressor.
An air conditioner that won't cool is a very common issue, especially during peak summer. Many people assume it's low refrigerant, but in reality there are many different causes. Pinpointing the right one helps you save on repair costs and prevent serious damage.
Below are the 10 most common causes and the most effective ways to fix them.
Quick overview of the 10 causes
- 1
Dust buildup on the indoor unit & filter
Cause #1 — accounting for 40% of no-cooling cases. Clean the filter every 2 weeks and perform a full cleaning every 6 months.
- 2
Low refrigerant
After 2–3 years of use or after relocation, refrigerant pressure may drop. A technician needs to measure the pressure and top it up.
- 3
Improper installation
Copper piping that is too long, has too many bends, or wasn't properly vacuumed — causes refrigerant loss and reduces efficiency.
- 4
Faulty compressor
The compressor is the "heart" of the air conditioner. When it fails, the fan still runs but there's no cooling. Replacement cost is 30–60% of a new unit's price.
- 5
Faulty indoor or outdoor fan
A weak or stopped fan means no heat dissipation, so the compressor can't pressurize refrigerant — and no cooling occurs.
- 6
Weak capacitor
An inexpensive but critical component. A weak capacitor makes the compressor start slowly or fail to start at all.
- 7
Leaking copper piping
Leaks at joints or caused by rodent damage. The refrigerant escapes completely, leaving only the fan running.
- 8
Wrong mode setting
Sometimes the unit is set to Fan or Dry mode instead of Cool. Check the remote before calling a technician.
- 9
Unstable power supply
Low voltage (< 200V) or constant fluctuations cause the compressor to underperform or fail to start.
- 10
Capacity mismatched with room size
Installing a 9,000 BTU unit in a 25m² room means it will never reach the desired temperature. Choose BTU based on the formula of about 600 BTU per m².
Details — Symptoms & Solutions
1 Dust buildup from long-overdue cleaning
Dấu hiệu
- Weak airflow
- Slow cooling
- Unpleasant odor
Cách khắc phục
- Clean the indoor and outdoor units regularly (every 3–6 months)
- Clean the dust filter
2 Low or empty refrigerant
Dấu hiệu
- The unit runs but doesn't cool
- Ice may form on the indoor unit
Cách khắc phục
- Check for leaks
- Refill with the correct refrigerant type and pressure
3 Improper installation
Dấu hiệu
- A newly installed unit won't cool
- Unstable operation
Nguyên nhân thường gặp
- No vacuum process performed
- Copper piping installed against standards
Cách khắc phục
- Inspect the entire installation
- Redo the work following correct technical procedures
4 Faulty compressor
Dấu hiệu
- No cooling at all
- Unusual noises
Cách khắc phục
- Inspect and repair, or replace the compressor
Requires a qualified technician to handle
5 Failed indoor or outdoor fan
Dấu hiệu
- The unit runs but produces no airflow or only weak airflow
Cách khắc phục
- Repair or replace the fan
- Check the fan capacitor
6 Weak or failed capacitor
Dấu hiệu
- Intermittent operation
- The compressor won't start
Cách khắc phục
- Replace with a new capacitor matching the correct specifications
7 Leaking or clogged copper piping
Dấu hiệu
- Cooling performance gradually decreases over time
Cách khắc phục
- Inspect the piping
- Reseal leaks or replace the pipe
8 Incorrect temperature setting
Dấu hiệu
- The unit runs but doesn't cool enough
Cách khắc phục
- Set a suitable temperature (25–27°C)
- Select the correct Cool mode
9 Unstable power supply
Dấu hiệu
- The unit operates weakly
- Constantly cuts out
Cách khắc phục
- Check the power supply
- Use a voltage stabilizer if needed
10 Overcapacity unit or poorly sealed room
Dấu hiệu
- The unit runs continuously but doesn't cool
Nguyên nhân thường gặp
- Room is too large
- Excessive heat gain (open doors, direct sunlight)
Cách khắc phục
- Choose a unit with the correct capacity
- Improve shading and insulation
An air conditioner that won't cool isn't always due to a major fault. In many cases, simple cleaning or adjustments are enough to fix the issue.
Bluebolt Services provides
Air conditioner cleaning
On-site inspection and repair
Installation that meets technical standards
Quick booking — a technician near you — transparent pricing. Bluebolt Services Hotline 0902 808 049.
Bluebolt Services
Need a professional installation quote?
Nationwide service · transparent pricing · 12-month workmanship warranty. Response within 24–48h.
