AC Running But Not Cooling in Chattanooga
The fan is going, air is moving, but nothing is cold. In Chattanooga this is our single most common summer call, and it is usually one of three parts.
In Chattanooga, a failed run capacitor is the most common cause of an air conditioner that runs but does not cool, and replacement typically costs $170-330.
A failed contactor costs $160-320 to replace in the Chattanooga area and takes under an hour.
Low refrigerant is never normal wear. A sealed system does not consume refrigerant, so low refrigerant always means a leak somewhere, and repair runs $250-1,500.
Match the symptom to the part
| What you notice | Most likely cause | Typical Chattanooga cost |
|---|---|---|
| Outdoor fan not spinning, humming sound | Run capacitor | $170-330 |
| Outdoor unit completely silent, indoor fan runs | Contactor or capacitor | $160-330 |
| Cooling weakly, longer and longer run times | Low refrigerant from a leak | $250-1,500 |
| Ice on the copper line at the outdoor unit | Frozen coil - see the frozen-coil page | $110-950 |
| Cools fine but house stays clammy | Oversized system or short cycling | diagnosis $80-150 |
| Warm air only in some rooms | Duct leak or blocked return | $150-800 |
Two things to check before you call
- Change the air filter. A filter choked with dust restricts airflow across the evaporator coil, and restricted airflow is the leading cause of both weak cooling and frozen coils. This costs a few dollars and fixes a surprising share of calls.
- Look at the outdoor unit. If the fins are packed with grass clippings, cottonwood fluff or Tennessee Valley pollen, the unit cannot dump heat and will struggle no matter how healthy the parts are. Rinse it gently with a garden hose from the inside out, with the power off at the disconnect.
About the capacitor
The run capacitor is a small cylinder that gives the compressor and fan motor the jolt they need to start. It is a wear part, it degrades faster in sustained heat, and Chattanooga summers give it plenty of that. The classic sign is an outdoor unit that hums but whose fan blade does not turn.
It is also the part most often used to overcharge people. A capacitor is an inexpensive component and the labour is under an hour, so a quote well above the $170-330 range deserves a question about what else is being replaced at the same time.
Common questions
Can I just add refrigerant every summer?
You can, but you are paying $250-750 a year to refill a system that is leaking into the atmosphere. Finding and repairing the leak costs more once and then stops. Any technician who recommends an annual top-up without ever looking for the leak is selling you a subscription.
Why does it cool at night but not in the afternoon?
That pattern points to a system that is marginal rather than broken - low refrigerant, a dirty condenser, or undersized capacity. At night the heat load drops enough for it to keep up. It usually gets worse, not better.
Is a hard-start kit worth it?
On an older compressor that is struggling to start, it can buy time for around $130-250. It is a stopgap, not a repair, and an honest technician will tell you which one you are buying.