Why has my AC unit stopped working suddenly?
Most sudden cooling outages come from simple, fixable issues such as a tripped breaker, a thermostat problem, or a clogged filter. If those quick checks don’t restore function, more serious faults like refrigerant leaks or a failed compressor may be involved and require a licensed HVAC technician.
Immediate checks you can perform safely
Before you call a technician, perform these quick, safe checks to determine if the problem is something you can fix without specialized tools.
- Check the thermostat: ensure it is on, set to cooling, and not in a restricted mode (like emergency heat or a very restrictive programmable setting); replace batteries if applicable and verify the display is clear and showing the target temperature.
- Inspect the outdoor condenser unit: clear any leaves, grass, or debris around the grille; ensure airflow isn’t blocked; if safe, verify the fan blade spins freely when power is on.
- Inspect the electrical panel and disconnects: locate the AC breaker or disconnect in the panel or at the unit; reset a tripped breaker and note if it trips again; replace any blown fuses with the same rating and check for underlying causes.
- Check air filters: a very dirty filter restricts airflow and can cause the evaporator coil to freeze, leading to little or no cooling.
- Listen for unusual signs: buzzing, sizzling, or burning smells indicate electrical or refrigerant issues—if you notice smoke or a strong burning odor, shut off power immediately and contact a professional.
If none of these steps restore cooling, or you are uncomfortable performing them, contact a licensed HVAC technician for a diagnostic.
Common mechanical and electrical causes
When simple checks don’t fix the problem, several frequent causes fall into the mechanical and electrical category. These issues typically require professional assessment and, in some cases, refrigerant handling or electrical work.
- Power supply problems: a tripped circuit breaker or blown fuse stops the unit from receiving electricity; resetting the breaker may help, but repeated trips require an electrical inspection to rule out overloads or faults.
- Thermostat or control issues: a miscalibrated thermostat, a failing sensor, or a malfunctioning control board can prevent the system from turning on or cooling properly.
- Electrical components wearing out: capacitors, relays, contactors, and fan motors degrade over time and can block the compressor or blower from starting or cause intermittent operation.
- Refrigerant leak or low charge: most newer systems use R-410A refrigerant; older systems may use R-22, which is being phased out and can be expensive to service. Leaks reduce cooling capacity and can cause the compressor to overheat; handling and charging refrigerant must be done by a licensed technician.
- Compressor or condenser problems: a failing compressor or a blocked/constrained outdoor condenser coil impairs cooling and often requires replacement or significant repair.
- Frozen evaporator coil: restricted airflow from a dirty filter or other blockage, or an improper refrigerant charge, can cause the evaporator coil to freeze—this stops cooling until the system thaws and the underlying issue is addressed.
- Drainage and safety switches: a clogged condensate drain line can trigger a safety shutoff on some systems; ensure the line is clear and the condensate tray is draining properly.
- Sensor and safety switches: high-pressure/low-pressure switches or temperature sensors can trip to protect the system; replacement or recalibration may be required.
Concluding paragraph: Because many of these issues involve electrical components or refrigerant handling, a professional diagnosis is often necessary to safely restore operation and prevent further damage.
What to expect from a professional diagnosis and repair
If you hire a licensed HVAC technician, here’s what typically happens during a diagnostic visit and subsequent repair plan.
- Initial interview and history: the tech asks about symptoms, when it started, and any prior issues or changes in usage.
- On-site inspection: assesses the outdoor unit, indoor air handler, thermostat, wiring, and refrigerant lines; checks for airflow problems and blockages.
- Electrical tests: checks voltages, capacitors, contactors, and safety switches to identify electrical faults or overloads.
- System pressure test: uses gauges to determine refrigerant charge and detect leaks; confirms whether the system is charged correctly and sealed.
- Defect diagnosis and cost estimate: outlines recommended repairs, parts, and labor, along with expected impact on cooling efficiency.
- Repair execution and testing: performs approved repairs, replaces faulty components, and tests the system to ensure proper operation and safety.
Concluding paragraph: Regular maintenance, including annual tune-ups and filter changes, helps prevent sudden shutdowns and keeps your AC running efficiently.
Summary
In short: start with quick, safe checks—thermostat, breakers, filters, and outdoor unit. If cooling still fails, the issue is likely electrical, refrigerant-related, or mechanical and should be handled by a licensed technician. Proactive maintenance can reduce the odds of sudden outages and extend the life of your system.
