Portable AC Maintenace Tips
Preventive Maintenance for portable or window air conditioners
Scotty
HVAC Oracle
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2005-08-06
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Portable or window air conditioners are an excellent choice for cooling a single room or and area where ducting cannot be used. Regularly is still required for best performance from these small units.
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The evaporator coil on the cool side should have a thin foam filters covering the face of the coil. The Filter should be removed and cleaned regularly. Once a month should be sufficient. These filters do not hold dirt well; if they are allowed to get dirty the dirt will pass through to the evaporator where it is harder to remove. If the coil face has become dirty, brush the coil face off with a soft nylon brush. Dirt allowed to build on the coil will become trapped between the fins and reduce the air. This will reduce the cooling capacity and can cause the coil to freeze.
On the other side, the condenser coil has no filters; it can get very dirty depending on the environment that it is running in. Flush out the coil with water at the start of each season, before it is installed. This will help to prevent the unit from overheating on the hottest days of the year when you need it the most. The dirt builds on the air inlet side of the coil, which normally cannot be seen. If you want to see how dirty the coil is you have to remove the outer cover to see the air inlet side of the coil. Remove the screws spread out along the sides of the air conditioner, and lift the cover. With a flash light look at the air inlet side of the condenser coil, through the fan blade. By spraying water from the outside of the coil with hose or pressure water you can push the dirt back out through the coil. If using a pressure washer is used, spray straight onto the fins and stay at least 12 inches away. A pressure washer can flatten the fins very quickly is you get to close. When cleaning, be careful not to spray water directly onto the motor or electrical compartment. Use a plastic bag to cover up any vent holes on the fan motor. Allow the unit to dry out for several hours before installing and plugging the unit in. Place the unit on an angle to allow the water to drain back to rear. Any water left in the bottom of the tray is going to spill directly down the front of your shirt when you pick up the AC.
Depending on the size of the unit, there will be 1 or 2 fan motors. Most of the small units use a single multi speed double-shafted fan motor for both the condenser fan and evaporator fan wheel. Give the wheel a spin, does it feel tight or does it spin freely. Does the shaft move vertically? Any vertical movement, up and down, indicates worn bearings. If the bearings are tight or there is movement, use a little extra oil to loosen the bearing up. The fan may run still and be noisy, but it will quit. With the price of new portable AC so low and labor being expensive you are better of to replace the whole unit then trying to change the fan motor. Functional replacement motors are available for most units if you want to try and change it. Look at the ends of the motor for oil ports. If there are no oil ports then the motor has sealed bearings and cannot be lubricated. If there are oil ports add a few drops of SAE 20-, which is lightweight electric motor oil with no detergent added. The recommend oil amounts are normally on the motor nameplate, if you can read them. Look around the outside of the fan blades is a slinger, which is used to throw the condensed water from the evaporator coil up onto the condenser coil. This help to eliminate the condensate water and provide additional cooling to the condenser coil. This slinger sits very close to the edge of the fan shroud, even a slight misalignment will cause this to rub and make the unit noisy. With the top casing remove the unit can shift a little and cause the fan wheel to rub the edge, make sure the unit is sitting on a flat surface and well supported.
The electrical wiring on the unit should be inspected for any signs of burning or over heating. Check the tightness of all the electrical connections, any loose connection will overheat and burn, which can cause the fan or compressor to fail. Remove the retaining clip on the compressor terminal cover. The gasket under the cover keeps moisture out of the terminal connections. The compressor can sweat when operating and the moisture can drip down into the terminal connections and cause corrosion. The molded electrical plug of the unit is a common area for electrical problems. If the forks are loose or discolored, replace the plug. After the unit is installed and operating and on a hot day, check the temperature of the plug and wall receptacle. If it feels very warm then there is a connection problem or a low voltage. This can be a serious fire hazard There should be a vent flapper near the discharge of the fan. This should have a cable attached to open and close the vent. The vent when open will exhaust air to the outside, this helps to keep the air fresh in the room. The air expelled by the AC will be drawn in elsewhere through air leakage in the room, eventually exchanging the total volume of the room.
When replacing the casing on the unit use extra caution around the condenser coil. The screws near the condenser may be shorter than the other. If the screw is too long you can puncture the condenser coil and release the refrigerant. Give the fan wheel a spin to make sure it is rotating freely. If you hear it rubbing, take the case off and check the position of the condenser coil and the fan wheel again. Adjust as required.
After the units has dried out, plug the unit in while still on the workbench to give it a test run. The work area must be above 70%F else the thermostat may not make to start the unit. First run the fan only and check all speeds- Does the motor sound quite- is the fan rubbing on anything at high speed or low speed?
Next turn the compressor on by lowering the thermostat or switch to cool mode. Listen to the compressor start. Does it start right away or does it hum then start or does it talk more then a 2 seconds to come up to speed? The compressor should start right away and sound smooth. A slow start may indicate bearing wear I the compressor or low voltage. Low voltage can be cause by using an under sized extension cord. If you are using an extension cord make sure it is a minimum #14 gauge wire and less then 50 feet long. If the compressor is loud or have a rattle, this may indicate worn valves and reduced pumping capacity.
If you are running the unit without the faceplate, air can short cycle from the discharge back into the intake of the evaporator. Place a piece of cardboard to deflect the air up and it does get sucked back into the unit. With a good thermometer measure the air discharge temperature. It should be ~15%F less then the room temperature. This varies depending on what fan speed you are using. The higher the fan speed the lower the TD, at low speed the TD will be higher 20%F or higher. A TD of 10%F or less indicates a problem. This could a low refrigerant charge, overcharged, weak compressor, high head pressure or a clogged capillary tube.
If all has checked out then your AC is now good to go, install the unit in the window or sleeve opening. Make sure the unit is secured in the window and has a slight slope to the back to allow for drainage. Wall mounted and window mounted units have a different configuration. The window mount units are design to sit in thin profile of the window. If used an opening cut into a outside wall, the condenser air intake will be partially blocked. Cutting off air to the condenser, which will causes the unit to run hot. This reduces the amount of cooling, increase the energy use and on a really hot day, the compressor will quit or the breaker will trip.
After the AC has run for an hour, check that unit is draining out the back or the water is collecting in the condenser fan area. You should be able to hear the water in the condenser fan.
Remember to periodically check for the water is draining out the back and feel the electrical plug and receptacle area for heat build on the really hot days. Do not run the AC when it is cool outside, especially on cool clear nights when the outdoor temperature can really drop. This often causes freezing of the evaporator coil. Pull the filter out once every 4 weeks and rinse it out with water. That's it, the unit should be good for the season.
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