Updated on Mar. 18, 2025
We'll show you easy DIY solutions for the most common central air conditioning repairs. You'll be up and running in no time, and you'll save the expense of a service call.
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If your central air conditioning system stops working during a brutal summer heat wave, you could be waiting days, if not weeks, for an appointment with a repair technician to fix it, and it’s probably going to cost a few hundred dollars. However, if you’re comfortable working around electricity and willing to spend less than $100 on parts, you can probably handle most common air conditioning repairs yourself in about two hours.
We talked to HVAC repair technician Glenn Gault to get the best do-it-yourself AC fan repair and maintenance tips. These tips will help you with the most common “low cooling” and “no cooling” problems.
You’ll need a few basic tools: multimeter, a voltage detector, an assortment of insulated screwdrivers and a socket set.
If these AC repairs don’t work, at least you’ve covered the most common failures, and your service guy can concentrate on finding the more elusive problem. Plus, with the new parts, you’ll likely add years of breakdown-free air conditioning. Here’s how to start.
If you have a central air system that includes ductwork, you’ll find a large metal housing attached to the plenum, which is where the ducts connect. This is the air handler, and it contains the blower that circulates air from the air conditioner and the furnace. If that blower isn’t working, you won’t get any air from the AC unit. Here’s how to check it:
Set your thermostat to cool mode and lower the thermostat temperature setting all the way. The fan should kick in. If not, try resetting the system circuit breaker. Next, check the outside condensing unit. The compressor (which sounds like a refrigerator) and fan should be running. If not, follow the troubleshooting and repair procedures shown here.
According to Gault, the most common cause of an air conditioner not turning on is a tripped circuit breaker. “If your AC is not turning on, the first thing to do is to check the breaker at your electrical panel and reset it if it’s tripped.” If that isn’t the problem, turn off the AC breakers in the main electrical panel before pulling the outdoor disconnect or removing the condensing unit’s access panel. Then use a voltage tester on the wires coming into the contactor to make sure the power is really off.
The AC contactor (relay) and start/run capacitor(s) (see illustration below) fail most often and are inexpensive. So it’s a safe bet to buy and install those parts right away, especially if your air conditioning service unit is older than five years. The condenser fan motor can also fail, but it runs about $150 — hold off buying that unless you’re sure that’s the culprit.
To buy replacement parts, find the nameplate on the condensing unit (not your furnace). Jot down the make, model and serial number (or take a photo). Get the parts at an appliance store, furnace dealer or online.
Central home air conditioner service systems consist of two major components: a condenser that sits outside your house and the evaporator coil (often referred to as an A-coil) that sits in the plenum of your furnace or air handler. The refrigerant in the A-coil picks up the heat from your home and moves it to the outdoor condensing unit.
The condensing unit fan blows outside air through the condensing coil to remove the heat. The condensing unit houses the three parts replaceable by a DIYer: the AC contactor, the start/run capacitor(s) and the condenser fan motor. The condensing unit also houses the compressor, but only a pro can replace that. The A-coil has no parts that can be serviced by a DIYer.
If the fan won’t start, the most common reason is the thermostat, says Gault, and after that, it’s the fuses and capacitor. Try setting the thermostat to its lowest setting, and if that doesn’t make the fan kick on, follow the directions below for checking the fuses and replacing the capacitor.
It’s really easy to clean an air conditioner condenser, and it’s one of the regular maintenance tasks that will extend the life of your unit.
Many disconnect blocks contain two cartridge fuses. Check them before you proceed with repairs. A blown fuse is a sign of a failing part inside the condensing unit. So don’t just replace it and think you’ve solved the problem. Instead, replace the parts, install new fuses, and fire up the unit. If it blows again, call a pro—you’ve got more serious issues.
Follow the electrical conduit from the house — that’s where you’ll find the access panel. With the power off, remove and store the access-panel retaining screws and remove the panel. Before you replace any parts, check for rodents’ nests or evidence of chewing on wires and electrical connectors.
If you find broken wires or chewed insulation and can safely handle electrical repairs, discharge the capacitor first. Then repair the wires and clean out the nest. Otherwise, call a pro. Here’s what you need to know about air conditioner wiring.
All air conditioning service units have at least one capacitor. The capacitor stores electricity and releases it during compressor and condenser fan startup to give both motors an extra jolt of power. And it smooths out voltage fluctuations to protect the compressor and condenser fan motor from damage.
Capacitors can degrade slowly, providing less startup power over time. Or they can fail in an instant. Gradual capacitor failure can go unnoticed for a long time, stressing the compressor and condenser fan motor windings, resulting in their early failure. Since capacitors are cheap, it pays to proactively replace yours about every five years. This is one of the most common air conditioning repairs.
WARNING: Discharge the capacitor before disconnecting wires or removing it from its bracket.
An AC contactor is a $25 mechanical relay that uses low-voltage power from the thermostat to switch 220-volt high-amperage current to the compressor and condenser fan. AC contactors can wear out and are at the top of the list of common air conditioning repairs. Even if your AC contactor is working, it pays to replace it every five years or so. Unscrew the old AC contactor before removing the wires. Then move the wires to the new unit.
AC units and thermostats have built-in delay features when they’re shut down and then re-powered. The delay can be as long as 10 minutes. And, if you’ve subscribed to an energy-saving device from your local power utility, the unit can take even longer to reset. If you’ve installed the parts shown and reinstalled the disconnect block, re-powered the circuit breaker, turned on the switch at the furnace, moved the thermostat to AC mode and lowered the temperature below the indoor temperature, and the unit doesn’t fire up after 30 minutes, it’s time to call a pro. Learn how to clean a central air conditioner unit.
