The operating principles of through-the-wall units, heat pumps, and other small self-contained air-conditioning systems are alike enough that some common remedial measures will help to keep them in peak working order:
1. Keep the evaporator and condenser coils clean. A good time to do this — as with most of these measures — is during the off season.
2. Change the filter or clean the filter element regularly. At the same time, clean the intake louvers and controls.
3. Be sure the airflow to and from the unit is not restricted in any way.
4. Keep the caulking in openings between the unit and window or wall frame in flexible, fresh condition to minimize infiltration and exfiltration.
The voltage available to the unit should be the full-rated voltage. This can be verified with a hand-held voltmeter. If the voltage is low, then either the wire size to the panel is too small (resistance losses diminish the available voltage at the point of use) or other elements on the circuit are drawing current that the packaged system needs. This equipment can be powered from other circuits, freeing an entire home run for the air-conditioning unit alone.
In the overall scope of the facility, self-contained systems are not very efficient, in which case several additional options are available:
1. A central control loop can be installed, which would involve nothing more than a single strand of wires looped between all the units, back to a central time clock. An override switch at each location would permit use outside of the scheduled hours.
2. Older units can be replaced with more efficient air-to-air heat pumps that have a higher energy efficiency rating.
3. If many units are to be replaced at the same time, it may be more economical to install a central system.
Depending on the scope of the renovation—if the ceiling space will be exposed, for example, making it easier to install ductwork there — and the location and type of existing equipment, the central system may not cost much more, and it will certainly use much less energy to operate.
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Excerpt from Energy Conservation Projects.