Overview: Central air conditioner failures and solutions
You can't cool off in front of the open
fridge forever. It's time to decide: You can
either wait four days for the service guy
to show up or try fixing your central air
conditioner yourself. I'll show you which
A/C failures can be handled by a DIYer
and how to safely replace the three parts
that cause the majority of all outdoor
condenser unit failures. You'll need a
standard multimeter, an insulated needle-nose pliers and ordinary hand tools.
I'll assume you've checked the A/C and
furnace circuit breakers in the main electrical
panel, as well as any cartridge fuses
in the outside disconnect. Replace all
three parts at once (about $150 total; see
“Buy the Right Parts,” below). Of course,
that might mean you'll replace some
good parts. But if the fixes work, your A/C
will be up and running much sooner and
you'll save about $150. Or you can replace
the parts one at a time and test the unit
after each one.
If these fixes 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.
Step 1: Make sure the problem isn't the furnace
Set your thermostat to A/C mode and
lower the temperature setting. If the furnace
fan kicks in, the problem isn't in the
furnace. If the fan doesn't run, try resetting
the furnace circuit breaker. If the fan
still won't start, call a pro—the fixes
shown here won't work.
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.
Turn off the A/C and furnace
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.
Step 2: Clean or replace the contactor relay
1 of 1
Photo 1: Blow out the contactor
Blow compressed air into all sides of the contactor relay
to clean out dead insects. If you're not able to remove all the
debris, you'll have to replace the contactor. Then try starting
The contactor relay switches power to
the condenser fan and the compressor. It
rarely fails. But it often gets jammed with
beetles, bugs and spiders that perished
checking things out. Remove the condenser
unit's access cover and locate the
contactor relay—it'll have at least six
wires attached to it. Try cleaning the critters
out with compressed air (Photo 1). If
that works, fine. But if you can't remove
all the fried bug parts, replace the contactor
with a new unit (about $30). Don't
think you can file the contacts to clean
them. That fix won't last.
Buy the Right Parts
Buy replacement parts from your local
appliance parts store or A/C dealer.
You'll need the make, model and serial
numbers from the nameplate on your
outdoor condensing unit—not the furnace
nameplate. Or, if you're willing to
pay for overnight delivery, you can buy
discount parts online (source1parts.com
is one site).
Step 3: Replace the capacitor(s)
1 of 2
Photo 2: Discharge the old capacitor
Attach a jumper lead to each end of the resistor pack.
Clip the other ends to insulated screwdrivers. Then touch the
screwdrivers to the capacitor terminals.
2 of 2
Photo 3: Swap capacitor wires to the new unit
Wiggle each wire off the old capacitor, noting the
terminal markings. Place the wire on the matching terminal
on the new capacitor. Then secure the new capacitor in the
The “start” and “run” capacitors store
electrical energy to jump-start the compressor
and fan motor. You may have a
combination start/run capacitor or two
individual ones. Both styles have a very
high failure rate, and when they go, the
compressor or fan won't start. They're cheap (about $30), so
First discharge any remaining electrical charge from the
capacitor(s) before you work on them. Fabricate a shorting
resistor pack by twisting four 5.6k-ohm, 1/2-watt resistors in
series (part No. 271-1125; about $1.25 at Radio Shack). Then discharge the capacitor (photo 2).
Next, move each wire lead from the old capacitor to the new
capacitor (photo 3).
Step 4: Replace the fan motor and restart the A/C
1 of 1
Photo 4: Install the new fan motor
Align the fan motor studs with the holes in the fan guard
or condenser cover. Then spin on the acorn nuts and
tighten. Install the fan blade and the electrical connector.
Tuck the new fan wires into the old conduit.
Remove the fasteners that hold the fan guard in place or
remove the entire cover assembly from the condenser unit. Lift
out the fan assembly and mark the bottom of the blade so you
replace it in the right direction. Then loosen the blade-retaining nut and pull it off the motor shaft. Disconnect the fan
motor electrical connector. Then swap in the new fan motor
(photo 4). Reconnect the fan guard or condenser cover.
Reinstall the access cover and the outside disconnect block.
Raise the temperature on the thermostat. Then flip the A/C and
furnace breakers to “On.” Wait 15 minutes for the thermostat
and furnace electronics to reset. Then lower the temperature
setting. The condensing unit should start up. If it doesn't, your
system may need more time to reset. Wait one hour and try it
again. If it still doesn't work, schedule a service call. Be sure to
specify exactly what you did. That'll keep the repair person from
replacing brand new parts, and you'll be able to have your work
checked by an expert.