Help, my (reverse cycle) air conditioner isn’t performing!

​As your air conditioner is often your largest energy user, it is worth getting the best out of it. In fact, if you have a modern high performance reverse cycle (heat pump) air conditioner you should probably use it for heating as well as it is likely to cost less than a gas heater. If this is the case, it will almost certainly be your largest single energy user.

Often, if an air conditioner is not performing as well as expected, it is not the air conditioner. the problem could be:

• excessive heat load (see the blog post Our house is too hot, what can I do?)
• dirty filter (see below)
• ​poor installation (This will be the subject of a future post)

​Of course it may be the air conditioner, particularly if it is old, and it may be worth getting a refrigeration mechanic to check it out.

Setting the Thermostat

Setting the thermostat correctly is critical to achieving comfort and minimising energy use. Setting the Temperature one-degree cooler than needed in the summer will cause a surprisingly large increase in energy use. Similarly setting the Temperature one-degree warmer than needed in the winter will also cause a surprisingly large increase in energy use.

Some old-style thermostats have a single temperature setting, and the temperature swings around that setting. Most modern ones have separate heating and cooling settings, which allow closer control. Normally it is best to set the temperature at 22 degrees for a single setting thermostat or at 20º for heating and 24º for cooling (possibly higher if you have ceiling fans) with a dual setting thermostat. For most air conditioners this would give a temperature of around 24 degrees for most of the summer and 20 degrees for most of the winter. If you can achieve comfort at a higher temperature in summer, or a lower temperature in winter, use the higher summer setting or lower winter setting as every degree change can save up to 10% of your heating or cooling energy.

In practice there are several factors that may require a different setting. For example, if in winter you get freezing air next to the windows sinking down and pooling at floor level, it may be necessary to set the thermostat at a higher temperature (although a better long-term solution would be to have honeycomb blinds or thick drapes with a pelmet to reduce the heat loss). To find out what the best solution is, it may be worth getting an energy audit as getting the right solution would save a lot more than the cost of the audit.

Often thermostats are not very accurate; this is not really a problem if you can find a single setting that achieves comfort all year round. However, it is probably necessary to occasionally tweak the setting.

You can find a suitable setting by randomly adjusting the thermostat, but if that doesn't seem to work, try the following approach:
1.On a day that is warm (to find the best summer setting) or cool (to find the best winter setting), but not an extremely hot or cold day.
2.Ensure the air conditioner has been running for at least one hour so the temperature is stable.
3.Initially set the thermostat to 22 degrees (for a single setting thermostat) or 24 degrees if you are setting cooling on a dual setting thermostat, or 20 degrees if setting heating on a dual setting thermostat.
4.Wait for a period of time (at least 10-15 minutes) to allow the air conditioner to stabilise again
5.If this hasn’t achieved comfort, set the thermostat slightly higher or lower, as seems appropriate. Don’t adjust it by more than a degree at a time or you will end up overcorrecting and take longer to find the best setting.

In summer, using ceiling fans may enable you to set the thermostat slightly higher. It will also significantly reduce the number of hours you need to operate the air conditioner.

Remember there are some problems that can’t be fixed by adjusting the thermostat. For example, if the air conditioner doesn’t have enough capacity due to the temperature of the day, adjusting the set point won’t make any difference to the room temperature. If this is the case, start with Cleaning Filters below, also see the blog post Our house is too hot, what can I do? Setting the thermostat also can't generally cure hot and cold spots, (refer Hot and Cold Spots below).
​
A future post will address basic troubleshooting of an air conditioner.

Maintenance requirements

All air conditioning systems require some routine maintenance. Cleaning filters is vital (refer Below). The outdoor unit also needs to be kept clear from leaves and other debris.

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Cleaning Filters

John bought an older home with ducted air conditioning. The second year they lived there, the air conditioner didn’t appear to be cooling as well. John asked me to look at it. The filter was completely blocked. After cleaning, the cooler worked fine! It had never occurred to John that he needed to do anything for the air conditioner and so the filter hadn’t been cleaned since the previous occupants left!

Filters require frequent cleaning because when they accumulate dirt, they block up, reducing airflow and hence the cooling capacity of the air conditioner. In residential air conditioners, filters are generally in hinged or sliding filter frames attached to the return air grille. These filters are generally of the washable type and should be cleaned by gently washing with water. However, check the manufacturer’s instructions first. If they won’t clean, use a mild detergent. As an alternative they can be vacuumed, however the cleaning frequency may need to be increased as vacuuming is not as effective. Most residential filters require frequent cleaning. I suggest you start with three monthly and increase or decrease if it seems appropriate. As a minimum, clean them at the start of each season.
When the filter gets torn or damaged it will need replacement

Hot and Cold Spots

Some homes have hot and cold spots, usually caused by an air conditioner serving areas that have windows facing different directions, or the difference between the old and new parts of a home.
It is possible to get ducted air conditioning controllers to give individual temperature control in each room, however this is still quite expensive. Most people must use judicious control of curtains or blinds to control temperature differences.
To save randomly trying different ideas, it may be worth getting an energy audit as getting the right solution first off, would likely save a lot more than the cost of the audit.

Adjusting the louvres

The aim in summer is to spread the cold air as widely and evenly as possible within the room. With the normal type of ceiling grille, the four or six segments can be rotated to direct air where required. If the louvres in the grille can be adjusted, direct the air along the ceiling. Try also to direct the air into the corners of the room. If using the air conditioner for heating, it may be necessary to adjust some (or all) of the vents downwards in winter.
If you have a wall split, try their automatic setting first for the louvre blades, but if it doesn't give the desired comfort, experiment with the manual settings.

General

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If you need personalised advice or you are thinking of spending some real money on air conditioning or improvements to the house, get an energy audit. I guarantee I can cost effectively save you the cost of the audit or the audit is free.

Feel free to leave a comment or question below.