The fan is blowing, the outdoor unit is humming, and the house is still warm. That pattern has a short list of causes. Some you can check yourself in a few minutes. Others involve refrigerant and need a mechanic. This guide covers both, then looks at outdoor unit noise and rebates.
Running but not cooling usually comes down to airflow, heat rejection or refrigerant
An air conditioner moves heat. The indoor coil above the furnace picks heat up from the house air. The outdoor unit dumps it outside. If air cannot get across the indoor coil, if the outdoor coil cannot shed heat, or if the refrigerant charge is wrong, the system runs and nothing much happens.
The common causes, roughly in order of how often they turn up:
- A clogged furnace filter. The furnace blower pushes the cooling air too, so a blocked filter starves the coil.
- A frozen indoor coil. Low airflow or low refrigerant drops the coil below freezing and it ices over. Air then stops passing through it.
- An outdoor unit that is not actually running. The indoor fan works, but the compressor or outdoor fan has stopped. A failed capacitor or contactor is a frequent reason.
- A dirty outdoor coil. Cottonwood fluff, grass clippings and leaves mat the fins and trap heat.
- Low refrigerant. A sealed system does not use refrigerant up. If it is low, there is a leak somewhere.
- Ducts too small for the cooling load. More on this below, because it depends on the age of the house.
Check these before you call
- Thermostat set to cool, fan set to auto, and the setpoint a few degrees below room temperature. A fan left on "on" blows warm air between cycles and can feel like a fault.
- Filter. Pull it and hold it to the light. If you cannot see through it, replace it.
- Breakers. Central air usually has its own breaker in the panel and a disconnect switch on the wall beside the outdoor unit. Check both.
- Outdoor unit. With the system calling for cooling, the top fan should spin and you should hear the compressor. If the fan is still and the unit hums, shut it off at the disconnect. Running it that way can damage the compressor.
- Outdoor coil. Clear plants, leaves and anything stored against it. Keep a clear space all round.
- Ice. Look at the larger copper line at the outdoor unit and, if you can, at the indoor coil. Frost or ice means a frozen coil.
- Supply registers open and return grilles not blocked by furniture.
If you find ice, turn the cooling off and run the fan only until it melts. That can take a while. Do not chip at it or use heat on it. When it has thawed, change the filter and try again. If it freezes a second time, the cause is likely refrigerant or a blower problem, not the filter.
Also check the condensate line. The indoor coil drains water while it cools. If the drain blocks, water can back up into the furnace or onto the floor, and some systems have a float switch that shuts cooling off to stop a flood. A wet floor beside the furnace or a system that cools then stops points here.
The house you live in changes the likely fault
Caledonia's housing falls into three broad ages, and each has its own cooling habits.
The Shetland Street area north of the river grew around the 1960s. Houses of that era were built with ducts sized for a standard gas furnace, not for central air. Cooling needs more airflow than heating. Push it through small ducts and you get weak flow upstairs, noisy registers and coils that freeze. Adding a bigger air conditioner makes it worse, not better. The fix is often duct work, or a ductless system for the rooms the ducts cannot reach.
The older homes around Edinburgh Square and Caithness Street were built long before forced air. Any ductwork there was added later and is usually cramped. Upper floors running hot while the basement stays cool is normal for these houses. Ductless heads are often the practical answer. See air conditioning installation.
Newer homes in Avalon have tight shells, mechanical ventilation and matched furnace and coil equipment. Here the usual summer faults are maintenance ones: blocked condensate lines, dirty filters, and ventilator filters nobody has changed since move-in. A seasonal tune-up catches most of these before the first hot week.
Refrigerant work is not a homeowner job
If the checks above do not solve it, the next steps involve gauges and refrigerant. In Ontario, refrigeration and air conditioning is a compulsory trade, which means a homeowner or general handyman should not be opening the sealed system. Topping up refrigerant without finding the leak only buys a few weeks. A proper repair finds the leak, fixes it, and charges the system to the manufacturer's specification. Work is performed by 313A refrigeration and air conditioning mechanics.
Neighbours can complain about outdoor unit noise
Yes. Noise from an outdoor unit is covered by municipal noise rules, and a neighbour can raise a complaint with the county. Haldimand County sets its own rules, so check the current version with the county directly rather than relying on what applied elsewhere.
In practice, most complaints start when a unit gets louder than it used to be. That change is usually a fault:
- A grinding or squealing fan motor bearing.
- A rattle from a loose panel, fan guard or refrigerant line touching the wall.
- A unit that has settled off level, so the compressor vibrates through the pad.
- A buzz or hard clunk at start-up, often a failing capacitor or contactor, or a compressor near the end.
Fixing the fault usually fixes the complaint. Newer subdivisions with narrow side yards put outdoor units close to the neighbour's windows, so placement matters more there. A few practical points:
- Do not box the unit in or wrap it in anything the manufacturer has not approved. It needs open air to shed heat, and a choked unit runs louder and longer.
- A solid fence or planting a short distance away can break up sound without blocking airflow. Follow the manufacturer's clearance distances.
- If you are replacing the unit anyway, compare published sound ratings between models. Variable-speed units spend most of their time running slower and quieter.
- Moving an existing unit is possible, but it means new refrigerant lines and electrical work, so it is usually only worth doing at replacement time.
Rebates in Ontario change, so check before you buy
Rebates for cooling equipment come and go, and the rules change between programs and years. Recent programs from governments and utilities have tended to favour heat pumps over air-conditioning-only units, because a heat pump also heats the house in winter. A heat pump looks and works like a central air conditioner in summer, so if you are replacing central air, it is worth pricing one alongside. See heat pumps.
Before you sign anything, check:
- Which programs are open right now, and whether they cover your fuel and equipment type.
- Whether an assessment is needed before the work. Some programs refuse claims for equipment already installed.
- Whether the exact model must be on an approved list.
- What paperwork the installer must provide. Keep the invoice, the model and serial numbers, and any assessment reports.
A rebate does not change whether the ducts can carry the airflow. Size the system to the house first, then see what the programs will pay toward it.
If the checks above did not bring the cooling back, book an air conditioner repair.