Central air conditioners have two separate components: the condenser and the
evaporator. The condenser unit is usually located outside the house on a
concrete slab. The evaporator coil is mounted in the plenum or main duct
junction above the furnace.
Most central air conditioners are connected to a home's forced-air
distribution system. Thus, the same motor, blower, and ductwork used for heating
are used to distribute cool air from the air conditioning system. When a central
air conditioner is operating, hot air inside the house flows to the furnace
through the return-air duct. The hot air is moved by the blower across the
cooled evaporator coil in the plenum and is then delivered through ducts to cool
the house. When the air conditioner works but the house doesn't cool, the
problem is probably in the distribution system.
Both the evaporator and the condenser are sealed. Therefore, a professional
service person should be called for almost any maintenance other than routine
cleaning. Central air conditioners should be professionally inspected and
adjusted before the beginning of every cooling season. However, don't let your
maintenance end with this annual checkup. While there aren't many repairs you
can make yourself, there are specific maintenance procedures you can follow to
keep your system operating at peak efficiency.
The evaporator for the central air system is located directly above the
furnace in the plenum. The evaporator may not be accessible, but if it is, you
should clean it once a year. If the plenum has foil-wrapped insulation at its
front, you can clean the evaporator; if the plenum is a sealed sheet metal box,
do not attempt to open it. Here's how to clean an accessible evaporator:
Maintaining the Condenser
In most air-conditioning systems, the condenser unit is located outside the
house and is prone to accumulate dirt and debris from trees, lawn mowing, and
airborne dust. The condenser has a fan that moves air across the condenser
coil. You must clean the coil on the intake side, so, before you turn off the
power to the air conditioner, check to see which direction the air moves
across the coils. Here's how to clean the condenser:
What You'll Need
You'll want to have these tools on hand to clean the condenser:
- Grass shears or pruners
- Spray bottle of coil cleaner
- Soft brush
- Fin comb
- Carpenter's level
- Pry bar or piece of 2-by-4
- Gravel or rocks
Step 1: Cut down any grass, weeds, or vines that have
grown around condenser unit; they could be obstructing airflow.
Step 2: Clean condenser with commercial coil cleaner,
available at refrigerator supply stores. Instructions for use are included.
Flush coil clean (do not use hose); let dry.
Step 3: Clean fins with soft brush to remove accumulated
dirt. You may have to remove protective grille to reach them. Do not clean
fins with garden hose, as water could turn dirt into mud and compact it
between fins. Clean fins very carefully: They're made of light-gauge aluminum
and are easily damaged. If fins are bent, straighten them with fin comb, sold
at most appliance parts stores. A fin comb is designed to slide into spaces
between fins. Use it carefully to avoid damaging fins.
Step 4: Check concrete pad on which condenser rests to
make sure it's level. Set carpenters' level front to back and side to side on
top of unit. If pad has settled, lift pad with pry bar or piece of 2-by-4,
then force gravel or rocks under concrete to level it.
During the fall and winter, outside condenser units should be protected
from the elements to prevent leaf blockage and ice damage. Cover the condenser
unit with a commercial condenser cover made to fit the shape of the unit or
use heavy plastic sheeting secured with sturdy cord.
Handling the Refrigerant
The coolant used in most air conditioning systems is a refrigerant called
Freon. Newer systems are likely using a replacement called Puron. If the system does not contain the proper amount of
Freon or Puron, little or no
cooling will take place. If you suspect a Freon or Puron problem, call a professional
service person to recharge the system. Caution: Do not try to charge your
system's refrigerant lines. Only EPA licensed technicians are legally
authorized to test or adjust your systems refrigerant.
Here's how you can repair the system's coolant lines. Examine the lines
running from the condenser outside the evaporator inside the house. If the
insulation is damaged or worn, it will cut down on the cooling efficiency of
the unit and, therefore, should be replaced.
Replace damaged or worn coolant line insulation with new insulation of the
same type as soon as possible. Follow manufacturer's instructions for
Many homes or apartments use window-unit air conditioners, so it's also
important to know how to maintain or service these smaller units. Learn how to
head off problems and keep these units running smoothly in the next section.
How to Troubleshoot a Window Unit
Publications International, Ltd.
Both of the major components of a room air conditioner
are contained in one housing. The condenser coil faces outside, and the
evaporator faces inside.
Room air conditioners, also called window units, work the same way
central air conditioners do. They are smaller than central systems and often
more expensive to operate. Depending on its size, a room unit may cool only
the room in which it's located, or it may be able to cool adjoining rooms as
Sandwiched between the coils are a compressor, two fans, a motor, and
thermostat controls. Dirt is the biggest enemy of window air conditioners; it
can lower the efficiency of the evaporator coil, block the operation of the
fan that blows out the cool air, clog filters, and block drain ports.
The coils, the compressor, and the motor of a room air conditioner are
sealed components, so any repairs to them should be left to a professional
service person. However, you can make minor repairs, and regular maintenance
will keep your unit running well. When extensive repairs are needed, you can
also save the cost of a service call by removing the air conditioner from its
mounting and taking it to the repair shop.
During the winter, room air conditioners should be protected from the
elements. Either remove the unit from its mounting and store it or cover the
outside portion of the unit with a commercial room air conditioner cover or
with heavy plastic sheeting, held in place with duct tape.
Caution: Before doing any work on a room air conditioner,
make sure it's unplugged. Room air conditioners have either one or two
capacitors, located behind the control panel and near the fan. Capacitors
store electricity, even when the power to the unit is turned off. Before you
do any work on an air conditioner, unplug it and discharge the capacitor or
you could receive a severe shock. The unit's owner's manual will show the
location of capacitors and tell how to discharge them. Otherwise, let an air
conditioning technician do it.
Maintaining Key Components
The filter, power cord, coils, switch, thermostat, drain ports, and fan are
important to service on a routine basis to avoid larger problems. Below are
guidelines on how to maintain these key parts.
At the beginning of every cooling season and once a month during the season,
remove the front grille and clean or replace the filter. If you live in a very
dusty area, clean or replace the filter more often. Most room air conditioners
have a washable filter that looks like sponge rubber.
Clean the filter with a solution of mild household detergent and water;
rinse well. Let the filter dry completely before reinstalling it. Some units
have a throwaway filter, similar to a furnace filter. When this type of filter
becomes dirty, replace it with a new one of the same type.
The power cord that connects the air conditioner to the wall outlet may become
worn and fail to supply electricity to the unit. To check the cord, remove the
control panel. Unscrew the cord terminals and then attach a test wire across
the bare lead wires.
Hook the clips of a volt-ohm-milliammeter (VOM) set to the RX1 scale to the
prongs of the cord's plug. If the meter reads zero, the cord is functioning.
If the meter reads higher than zero, replace the cord.
Evaporator and Condenser Coils
Clean the evaporator and condenser coils at the beginning of the cooling
season and every month during the season. If you live in a very dusty area,
clean the coils more often. Use a vacuum cleaner on these components.
If the fins on the coils are bent, straighten them with a fin comb, sold at
most appliance parts outlets. A fin comb is designed to slide into the spaces
between the fins. Use it carefully as the fins are made of light-gauge
aluminum and are easily damaged.
The selector switch, located directly behind the control panel, turns the unit
on. If the air conditioner does not run at any setting, and it is receiving
power, chances are the switch is faulty. To correct the problem, remove the
control panel and locate the switch. Check the switch terminals for burnt
insulation or burn marks on the terminals. If you see any indication of
burning, replace the switch with a new one of the same type.
The switch is held to the control panel or frame with screws; unscrew it
and connect the new one the same way. If you determine the problem may not be
the switch, call a professional service person.
Maintaining the thermostat and drain ports on your home air-conditioning
window unit is vital to keep the whole system working properly. It won't be a
difficult or burdensome task if you folllow the guidelines mentioned below.
The thermostat is located behind the control panel. Here's how to test and/or
replace the thermostat:
What You'll Need
You'll want to have these tools on hand to test or replace a
- Volt-ohmmeter or multimeter
- Replacement thermostat
Step 1: Remove grille and control
panel from unit. Thermostat has special sensing bulb attached to it; this part
extends from thermostat into evaporator coil area. Its role is to sense
temperature, which is controlled by thermostat.
Step 2: Remove thermostat carefully
because you must return sensing bulb to identical spot later. To make
replacement easier, tag location of bulb before you remove thermostat.
Step 3: Check thermostat with VOM
set to RX1 scale. Clip probes of tester to thermostat terminals, and turn
temperature control dial to coldest setting. If meter reads zero, thermostat
is functioning properly. If reading is higher than zero, replace thermostat
with new one of same type. If thermostat is held to control panel or frame
with screws, clips, or metal tabs, connect new thermostat the same way the old
one was connected.
Note: If the thermostat has more
than two lead wires connected to it (not counting the sensing bulb wire) do
not try to test or replace it. Instead, call a professional service person.
As the air conditioner operates, condensed moisture and water vapor from the
evaporator coil are funneled through drain ports or an opening between the
partition in the middle of the evaporator coil and the condenser coil. At this
point, the fan blows the moisture against the condenser coil, where the water
Drain ports can become clogged with dirt. The result is water leaking from
the appliance, usually through the bottom of the grille. To prevent clogging,
clean the ports with a short piece of wire hanger or the blade of a
pocketknife. Do this at the beginning of every cooling season and every month
during the season. Also check the condenser side of the air conditioner. Some
models have a drain port along the bottom edge of the cabinet frame. If your
air conditioner has this drain port, clean it out when you clean the other
The fan, motor, and compressor require routine maintenance to keep your
air-conditioning unit running at its most efficient. The following are some
When a fan malfunctions, the problem is usually loose or dirty
blades. If the fan won't operate or if it's noisy, cleaning and tightening
will usually fix it. Here's how to repair a room air conditioner's fan:
What You'll Need
You'll want to have these tools on hand to repair a room air
- Soft cloth
- Screwdriver or Allen wrench
- Long-blade screwdriver
- Wrench 20-weight non detergent motor oil
- Volt-ohmmeter or multimeter
Step 1: Open cabinet and locate fan.
Step 2: Clean away any debris with vacuum and soft cloth.
Step 3: Check fan blade on motor shaft for looseness.
Blade is fastened to shaft with setscrew at hub of blade.
Tighten setscrew with screwdriver or Allen wrench. If air conditioner has
round vent fan, tighten fan on motor shaft by inserting long-blade screwdriver
through port in fan.
Fan is installed in its housing with bolts, and vibration can loosen
these fasteners. Then tighten them with wrench.
Step 4: If fan has oil ports, apply
several drops of 20-weight nondetergent motor oil (not all-purpose oil) to
each port at beginning of cooling season.
Step 5: If you suspect fan motor is faulty, test it with
VOM set to RX1 scale. Disconnect terminal wires from terminals, and clip
probes of VOM to wires.
If meter reads between about 3 and 30 ohms, motor is functioning properly.
If meter reads either zero or an extremely high number, replace motor.
To remove the fan motor, remove the fan, the power wires, and several
mounting bolts. Install the new motor with the reverse procedure. However, if
the condenser coil must be moved to get the fan out, do not try to remove the
motor. Call a professional service person.
Motor and Compressor
If problems occur in the motor or compressor of the air conditioner, call a
professional service person.
By following the routine maintenance mentioned in this article, you will be
able to handle most problems that occur with your central air conditioning or