As we hurtle towards what is a scorching summer period for most of us in Australia, many of us will retreat indoors in the hottest part of the day to enjoy the cooling bliss of an air conditioner. Air conditioners — both split and ducted systems — consist of piping and lines, outdoor and indoor units, airflow outlets, and various connections and controls. And each of these components can eventually start underperforming or breaking down.
One of the elements of an air conditioning system that can cause a lot of problems is the thermostat. Here is our guide to air conditioner thermostat troubleshooting, including what can go wrong and whether you can find a DIY solution or not.
What air conditioner thermostats do
We rely on the thermostats in air conditioning systems to give us accurate temperature readings and ensure the required adjustments to the air conditioning unit’s temperature are made. Essentially, if the thermostat is not working correctly, you cannot effectively communicate with your system and your comfort levels and the unit’s energy efficiency could be compromised.
Air conditioner thermostat location
In terms of air conditioner remote control symbols, many models have visually similar symbols. (Check out our blog — What Every Daikin Air Conditioner Symbols Means — for a guide). In terms of the air conditioner thermostat location buttons on your remote, the two important ones to refer to are:
General air conditioning issues
Most of the common air conditioning problems and solutions apply to any type of system, but some are specific to each, whether it be a split or ducted system. Here are the top 6 air conditioning issues:
- Your unit has airflow problems, is short cycling or won’t turn off or on
- Your unit is blowing air that’s either too cold or too hot
- Your unit is leaking refrigerant or water
- Your unit is noisy or emitting strange smells
- Your energy bills have dramatically increased
- Your unit requires frequent repairs
Signs you may have thermostat issues
There is a range of issues that can indicate problems with AC thermostats, usually evident in noticeable external signs, including:
Your unit is not cooling or heating properly
One of the most common air conditioner issues is units that are producing air that’s inconsistent with your chosen settings. Air conditioners are meant to provide a consistent air temperature, and if your system stops producing warm or cool air when you need it, it could be due to a range of issues. Possible causes are:
- a dirty condenser unit
- frozen evaporator coils due to blocked filters
- dirty or frozen condenser coils
- electrical issues with the condenser fan motor and wiring
- a leak in the refrigerant line
- low refrigerant
- damaged or clogged-up ducts
- vents not open (or only a few are open)
- a broken thermostat (ducted systems)
- insulation issues (ducted systems)
- air loss due to misaligned ductwork (ducted systems)
The above can all result in your AC system not cooling your property sufficiently or at all! Most of them can also lead to overheated interior AC units.
In terms of solutions, you can fix some non-technical issues yourself. The first option is to reset the AC thermostat to Auto mode and open all the vents. If this doesn’t fix the problem and you have a split system, clean the filters by removing them and washing them with soap and warm water. Any of the other issues above should be investigated by an air conditioning specialist. Filters on ducted units are also not typically accessible to homeowners, so again, contact a professional.
Your unit won’t turn on
This issue can be frustrating, particularly if it happens unexpectedly and it’s a scorching hot day outside! Possible causes are:
- flat batteries on your AC remote control or thermostat
- wrong thermostat settings
- tripped AC circuit breaker
- a blown fuse
- a damaged motor or compressor
Some of the causes behind your AC system not turning on can be simple and easy to fix yourself, whereas others will definitely require the expert skills of a licensed professional. First up, check the batteries in your temperature control devices and replace them if necessary. If that doesn’t work, check the thermostat settings are as they should be (for example, in the Cooling mode and at the desired temperature).
It’s also worth checking that the outdoor condenser is running, as sometimes lowering the temperature by around ten degrees can resolve the issue. However, programming and calibrating thermostats can be tricky, so we definitely recommend you contact your air conditioning technician.
Your unit won’t turn off
The central AC system is designed to turn itself on and off via the thermostat. So, if it fails to do that, there is a problem. Possible causes are:
- your unit size is not conducive to the size of your property (meaning your system will struggle to turn off as the desired temperature level is never reached)
- a short in the thermostat wires
- a broken thermostat
- issues with the fan relay switches
- inappropriate refrigerant levels
The only DIY solution with this issue is switching your system off by turning the thermostat fan to the “off” mode. If you still can’t turn the system on again, then it is a gas or electrical-related issue that needs a professional.
How to fix an ac thermostat
We have offered some solutions on how to fix an AC thermostat above. However, it’s worth mentioning that anything other than simple maintenance (like cleaning filters, vents and outdoor units) shouldn’t be attempted by yourself. This is because DIY troubleshooting carries more risks than benefits. Risks include:
- Additional costly repairs — Repair attempts on one part of your system can lead to the serious breakdown of another.
- Safety issues — Dealing with electricity, toxic fumes and dangerous pressurised gases can pose serious health and safety risks.
- Compromised efficiency — High monthly operational costs and sub-standard efficiency are often the result of unqualified AC repair work.
- Invalid warranties — Manufacturers put warranty conditions on products for a reason. Any unauthorised repairs may lead to your air conditioner’s warranty becoming void.
So in terms of air conditioner thermostat troubleshooting, our advice is to call in an expert. If you have done your general cleaning maintenance and still have an issue, it’s more than likely it is something more serious that requires professional servicing.
- Matt Mouritz, 2017, Ducted Air Conditioning: Is Your Thermostat Broken? Mouritz
- 2020, Air Conditioner Troubleshooting: Problems and Solutions, Fantastic Services