Professionally installed air conditioning is reliable and easy to operate, but anything mechanical has the potential to develop a fault eventually. Regular servicing and maintenance is your best defence but here are some of the most common issues we’ve listed below for you.

User error

If your bills are high and the building isn’t cooling, make sure nobody is responding to hot weather by throwing open the windows. If you’re running an air conditioner with open windows, you are effectively trying to cool the entire planet. It won’t work and you’ll run up a hefty bill trying. Air conditioners need to operate upon sealed zones in order to do their job.

Compressors occasionally switch off if they overwork on a hot day. Don’t panic and call an engineer until you’ve had a look for the reset button. Also, check for a tripped breaker.

Refrigerant problems

The efficiency of an air conditioner depends on it containing the optimum amount of refrigerant; not less and not more than the manufacturer’s recommendation. However, most systems leak a small amount over time and need to be checked regularly. Soldered joints can also crack and leak suddenly. Refrigerant gases are strictly controlled under UK and EU regulations so any handling of refrigerants must be performed by a properly licensed person. A certified technician will fix any leaks, test the repair, and top up to the correct level.

Inadequate maintenance

Filters get dirty. They’re meant to, but if you don’t clean or change them, it becomes harder for air to pass through freely. This causes the system to work harder, use more electricity and accelerates the wear on other components. The same is true of the condenser, cooling coils, fans and other parts of the system. A regular maintenance regimes save money in both the short and the long term.

Electrical failures

Wires and terminals slowly corrode: this is one of the many aspects that a technician checks and cleans on a service visit.

Eventually, electrically-driven components such as the compressor and fan will need to be replaced or reconditioned, but you can delay this cost by ensuring that your system is matched in power to the size of the building. When it isn’t, it can switch on and off too often and it’s the constant switching more than anything else that wears out electrical components. Ask for an engineer to assess this for you if you think it could be a problem.


Malfunctioning or poorly positioned thermostats and other sensors can have a similar effect, causing your system to switch on and off too often. The most important one is located near the cooling coil and air inlet. Make sure that it isn’t actually touching the coil.

Drainage issues

Evaporators produce a condensate that is supposed to drain away. Make sure that outlets don’t become clogged and that any wall mounted evaporator units are still level, because this affects their ability to drain.

If there are signs of water leaking near the coils it could be due to ice formation. Most often this indicates that the airflow is inadequate, so check that your filters are clean and your air inlet vents are clear.

Air inlet blockages

The vents that draw air into the building, or into your external compressor if you have one, can become blocked with all kinds of strange things. Crisp packets are quite common, as are windblown leaves and even wasps nests and nesting birds. Be sure to give them an occasional check. External vents can be secured behind mesh baskets, which can help but this isn’t foolproof.

Hot and cold areas

If you have a properly zoned air conditioning system, you shouldn’t have a problem with one area being too hot and another too cool. If this develops over a period of time, look for leaks in ducts; joints can separate, cracks develop, or someone can decide to drill a hole in one to pin up a calendar (it happens).

If there are no leaks and the problem has always been there, it could simply be that a room is receiving far more heating from the sun than others. You can alleviate this with thermal blinds or by applying a filter coating to the window glass.


Flapping sounds are most likely something caught in the blades of the fan – something you can easily check, but be sure to turn off all power before removing any covers.

Screeching or rattling sounds could indicate a more serious fault developing, for example, worn motor bearings. It’s wise to ask an engineer to check this out for you in good time: air conditioning systems have a habit of failing precisely when you want them the most, such as during a heat-wave, and that’s when everyone else is calling out engineers too. Regular maintenance catches any issues developing before they become emergencies.

Still have questions about air conditioning, then why not check out our handy A to Z of air conditioning terminology. Or if you can’t find what you’re looking for there, give one of our friendly air con engineers a call on 0117 322 6150 or drop us an email.