Question

What might need to be replaced if your home air conditioning and heating stopped working?

Answer 1

If both your home air conditioning and heating stop working, the faulty item could be one of several components. Before replacing parts, check simple things: thermostat settings and batteries, the air filter (dirty filters can shut systems down), that power switches are on, and the circuit breaker or any HVAC fuses/trip switches.

Common parts that may need replacement, with typical signs and whether a pro is recommended:

- Thermostat — blank or unresponsive display, wrong temperature control. Often replaceable by a homeowner if you’re comfortable.
- Thermostat batteries — easy DIY fix if display is dead.
- Air filter — if clogged, replace immediately (DIY).
- Circuit breaker or fuse — if tripped or blown and retrips, electrician or HVAC tech needed.
- Control board / furnace PCB — intermittent or no response, erratic operation. Usually replaced by a technician.
- Transformer — low/no 24V control power; pro recommended.
- Contactor (outdoor unit) — outdoor fan/compressor won’t start; tech replacement recommended.
- Start/run capacitor(s) — humming, fan/compressor won’t start, or slow startup; often replaced by a technician (can store lethal charge).
- Compressor — AC won’t cool and outdoor unit won’t start or is seized; major repair/replacement by pro.
- Condenser fan motor or blower motor (indoor) — fan not running, poor airflow; usually replaced by a technician.
- Blower motor capacitor or relay — weak airflow or no blower; tech replacement.
- Refrigerant leak / TXV or expansion valve — loss of cooling; a certified HVAC tech must repair and recharge refrigerant.
- Reversing valve (heat pump) or defrost control — heat pump won’t switch to heating or freezes up; pro replacement.
- Igniter/pilot assembly, flame sensor, or gas valve (furnace) — furnace won’t light or keeps shutting off; tech required (gas safety).
- Heat exchanger — cracked heat exchanger causes no heat or dangerous CO—immediate professional assessment and usually major repair/replacement.
- Limit or safety switches, float switch (condensate) — unit shuts down due to safety; a tech should inspect/replace.
- Condensate pump or clogged drain — AC shuts off due to float switch; homeowner can clear drain or replace pump.
- Ductwork/vents/dampers — poor airflow or inconsistent temperature; repairable by HVAC or duct specialist.
- Whole unit (furnace or AC) — if very old/inefficient, replacement may be more cost-effective than repairing major components.

Safety: Don’t attempt gas, refrigerant, or high-voltage electrical work yourself. If you’re unsure or the problem involves gas, refrigerant, or major electrical components, call a licensed HVAC technician.

If you tell me the symptoms (no power, no airflow, noise, trips breaker, heating only, cooling only, age of equipment), I can suggest the most likely causes and next steps.