Air Conditioner Troubleshooting,
Tips From A Pro
Before you call the repairman, try this basic air
conditioner troubleshooting guide. This guide and our SYMPTOM CHECKER will help
you to diagnose problems with your typical ducted split type air conditioner. A
repairman will cost you about one hundred dollars per hour. With a few household
tools and a little bit
of knowledge, you can do it yourself and save that money. (You provide the tools
and we will help with the
You should ensure that the routine maintenance
has been performed on the unit. If the air filter has not been changed in the
past month, check to see if it is dirty.
You can use the HvacRepairGuy interactive troubleshooter. LAUNCH
the video on Youtube
At the Thermostat
**NOTE** ONLY YOU CAN ASSESS YOUR ABILITY TO PERFORM
THIS TASK. THIS IS A GUIDE AND CANNOT PROVIDE ALL OF THE DETAILS FOR
Begin your air conditioner troubleshooting at the
thermostat by ensuring that the thermostat is on cool and that it is set
lower than actual room temperature. This is to ensure that there
really is a problem. It may seem silly but that is the first
thing a repairman will check and you will normally still be charged a
service call even if that is the only problem.
Is there air coming out of the floor or ceiling
If there is not, then, check to see if the fan on
the outside unit is running. If the fan on the outside unit is not
running either, check to make sure that the breakers for the furnace/air
handler and the air
If the breaker is not tripped, then the problem may
be your thermostat,
the furnace/air handler control
board, or the wires between the furnace/air handler and the
If your unit has a condensate pump, check to make
sure the reservoir is not full. If the reservoir is full, a limit switch
will normally stop the air conditioner from running. You will need to
repair or replace the pump.
If the breaker is tripped, you can reset it by shutting it
off and then turning it back on. If it trips again, then check the
wiring in the
furnace/air handler for signs of damage and repair as necessary.
If the blower is running but the fan on the outside
unit is not, then continue your air conditioner troubleshooting at the
Is the fan on the outside unit
blowing out hot air?
If the blower isn't running but the fan outside is,
the problem could be the blower
motor, it's run
capacitor, or the furnace/air handler control
If the fan motor is not running, then shut the
power off to the unit. Then check all wire connections for signs of
damage such as burning and repair as necessary. You should also check
the wire connections in the
compressor terminal box and repair if necessary.
You can use our capacitor
testing guide to check the unit's capacitors and replace as
Continue your air conditioner troubleshooting by turning
the power back on to the unit and observe whether the contactor closes
or not. If the
unit does not start, look for a reset button. Some units have a high
pressure cutout switch that can be
reset. Then, use a voltmeter to check to see if you have power to the
unit and 24 vac to the contactor's coil. If you do
not have power to the unit, you should check the wiring between the
electric panel and the
unit. If you do not have 24 volts to the contactor's coil, check the
thermostat and the low voltage wires from the furnace/air handler to the
condensing unit. If you have power
to the unit and the coil on the contactor but the unit does not start,
the unit's contactor
may be bad.
If the compressor starts but the fan does not, the
could be the problem.
If the condenser fan starts but the compressor does not,
the unit may be low
on refrigerant, the compressor might be too hot, or the compressor
might be bad.
Do you see ice on the lines connecting the indoor and
outdoor units or is there water around the furnace?
If the blower on the furnace is running, check to
see if you see any frost or ice around the units. You might also notice
water around the furnace. Is there ice on the copper lines going
outside? If yes, then shut the outside unit off for a couple of
hours but let the blower on the furnace run. This will allow the ice to
After two hours, you can continue your air
conditioner troubleshooting. Turn the ac back on and let it run for
about five minutes. Now feel the larger copper line at the outdoor unit.
This should be cold and have condensation on it. If it is not
cold or if frost is forming on the line, it
is probably a freon problem. You will need to call a repairman
because of federal refrigerant usage regulations.
If there is no ice or frost, then continue
troubleshooting at the outside unit.
Air Conditioner Troubleshooting,
If the condenser fan and the compressor both run but the
cooling effect is not adequate, you should check the temperature drop of
**NOTE** The unit should be operating for 10-15 minutes prior
to taking temperature measurements.
To measure the temperature drop, measure the air
temperature leaving the air handler and subtract it from the temperature
of the air entering the air handler. The result should be about 15
degrees for a high efficiency unit and about 18 to 20
degrees for an older unit (SEER less than 10). If the temperature drop
is significantly lower than that, the problem may be the refrigerant
If the temperature drop is significantly higher than that,
then your air conditioner troubleshooting should focus on the system's
air flow. The evaporator coil, filter, or blower wheel could be dirty.
This is usually the result of not performing routine maintenance on the
system. It could also be caused by a duct system that is too small. This
is usually the result of improper design or installation. You may be
able to increase the blower's cooling speed or replace your existing
blower motor with a variable speed motor to overcome that problem.