An air conditioner that runs but doesn’t cool is one of the most common faults. The cause can range from simple maintenance issues to refrigerant problems. Here’s how to work through it.
Common causes
- Low refrigerant (a leak) — reduced cooling, possible icing, abnormal pressures
- Dirty filters or coils — restricts airflow and heat transfer
- Blocked condenser — poor heat rejection outside
- Faulty compressor or capacitor
- Thermostat or control issues
Start with the simple checks
Clean or replace filters, clear debris from the outdoor unit, and confirm the thermostat settings. Poor airflow is a surprisingly common cause of weak cooling.
Then check the refrigerant circuit
If airflow is fine, take pressure, superheat and subcooling readings. Low charge points to a leak that must be found and repaired — not just topped up. High pressures suggest a condenser, airflow or overcharge issue.
FAQ
Does an air conditioner need regassing regularly? A sealed system shouldn’t lose refrigerant — if it’s low, there’s a leak to fix rather than a routine top-up to schedule.
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