The laws of physics play an important role in air conditioning system, or also known as AC system, to cool enclosed air: Heat is absorbed when conversion of liquid to gas takes place. This process is known as phase conversion.

Air conditioners use this law to its advantage by making some chemicals go through the cycle of evaporation and condensation repeatedly in an enclosed arrangement of tubings.

These chemicals are known as refrigerants. They also have the ability to change at rather cold atmosphere. Air conditioners also have fans that push warm air over these coils filled with chilled refrigerants. Actually, central air conditioners contain this complete system of tubings whose purpose is to maneuver air to and fro these chilled coils.

When warm air flows over the cold, low-pressured evaporator coils, the chemical inside these tubing takes in the heat, and thus becomes a gas from a liquid state. Then the refrigerant gas goes through a compressor in high pressure in the air conditioner to become a liquid again. However, undesired heat is produced in this mechanism. This additional heat is released to the outside of the apartment by a second set of tubing, known as condenser coils, and a second fan. This sequence is then formed: The refrigerant gas is chilled and reverts to liquid state.

Thus the continuous cycles ensues - liquid refrigerant, changes to gas after taking in the heat from the air, gets compressed to become a liquid again.

Picture source: How stuff works

The main function of an air-conditioner (or A/C) is to chill indoor air. But they also keep track and maintain air temperature through a thermostat.Air-conditioner also comes with a filter to take away airborne materials in the room. Not only that, air-conditioners also act as dehumidifiers. As temperature is a critical part of relative humidity, decreasing the air temperature will help in removing a part of the moisture in the air. Because of this there should be drains to collect the water condensed when air-conditioners work on humid days.
In anyways, the main processes of an air-conditioner are to control refrigerant flow and regulate air in two directions: indoor and outdoor.
These are the main parts of an air-conditioner:

• Evaporator - Receives the liquid refrigerant
• Condenser - Removes heat energy through heat transfer
• Expansion valve - control refrigerant flow into the evaporator
• Compressor - A pump that pressurizes refrigerant

The chilled side of an air-conditioner has the evaporator and a fan that will move the air towards the cold tube and towards into the indoor. The warm side has the compressor, condenser and another fan to push the warm air to the outside of the apartment. The expansion valve is situated between the 2 coils. The main purpose is to control the level of compressed liquid refrigerant flowing back to the evaporator. As the pressure in the evaporator is low, the refrigerant will expand and becomes a gas again. The compressor facilitates this process by pressurizing the refrigerant gas and changes it back to a liquid. These are the main parts of an air-conditioner, on top of other accessories like sensors, timers, valves etc.
This is the standard, conventional system for an air-conditioner. There are other varieties of air-conditioner in the market now as listed below. We will look into details for some of the common ones in Singapore. Window air-conditioners - They consist of all these parts mounted into a metal box that is installed into a window opening. The hot air is removed from the back of the air-conditioner, while the condenser coils and a fan chills and circulates indoor air in a continuous cycle. Split-system air-conditioner - as the name suggest the system splits the hot side from the cold side. Please refer to the dedicated section on split-system air-conditioner for details.
The larger air-conditioners such as the central air-conditioning system perform slightly differently. They share a control thermostat with the apartment heating system, and the following are not located in the apartment - the compressor and condenser and the hot side of the unit. These are separated in a weatherproof enclosure in the outdoors. Usually the external condensing unit is mounted in locations like the top of the roof for big buildings.

Let's focus on split air conditioning system as this is the most common system for residential units and buildings here.

Picture source: Nick's maintenance Service
A split air conditioning system simply means that the condenser (or sometimes referred to as the "outdoor unit") is separated from the "indoor unit", thus the term "split".
In residential apartments or small offices, split air conditioning system is the most common air conditioner system applied. This system has at least 1 unit that is located in the apartment. The compressor is located outside of the room - either on the ground or onto wall brackets.
A split air conditioning system is the most suitable system compared to wall, window or centralized air conditioner systems for residential properties. It effectively cools a standard-sized house without the need for complicated installation that will have higher costs and effort, as they do not require ductwork.

Components and Function of a Split Air Conditioner

Picture source: How stuff works
The compressor that is placed outdoor will kick start the chilling of the air, and the evaporator and the blower make up the indoor portion. These 2 parts are connected by a series of wiring and coiling to move air between them. A thermostat is the main controller of the compressor. As the hot air comes in contact with the thermostat, the compressor is then initiated. Refrigerant gas is circulated, increasing the pressure and temperature of this chemical as it moves through a coil of tubes towards the condenser.
A chilling method is applied to remove the heat from the refrigerant gas in the condenser for it to become a liquid. Then the refrigerant liquid is forced through the tubes indoors as it approaches the evaporator.
As it moves in the indoor the heat from the liquid is released and the fan maneuvers the warm air over a container which consists of the cold liquid refrigerant. The fan system then blows this cold air into the apartment, achieving the main purpose of decreasing the temperature of the room. This process continues as long as the thermostat is in contact with the air that is hotter than the set temperature. This set temperature is usually determined by a remote control. Different rooms of the building can have different temperatures set.

Advantages of a split air conditioner system compared with other systems
Since a split air conditioner is small and separated among the 2 compartments, there is minimal chance for the heat energy to dissipate from the system. In centralized air conditioning system, which uses the duct system, results in a lot of the energy being wasted. This issue is not present in the split air conditioning system.
Split air conditioning systems are also better compared to window or wall air conditioning units. Window air conditioner units and wall air conditioner units are small and installation work is simpler but they are not efficient in cooling big apartments or numerous rooms. Even with good handy work to install these units to seal up any gaps, heat is still coming into the space for these systems, and thus wasting the efficiency of these air conditioners. Comparatively, split air conditioner is smaller, more cost effective and easy to operate and maintain. This system, once set by the professional as there are still some technical work such as wiring and installation of the air conditioner sets, is a low cost and energy saving method of air cooling in the apartment.

 

Another pretty common air-conditioning system is the window air-conditioner. This unit is made to fit into a standard window frame. This system contains:

• A compressor
• An expansion valve
• A hot coil (on the outside)
• A cold coil (on the inside)
• Two fans
• A control unit

The principle of how this system works is that the fans move the air over these tubes to assist in the dissipation of heat of the warm air to the outside and to cool the air in the room.
The window air-conditioning system is usually limited in cooling to 1 room. They will not be efficient in handling multiple rooms as too much energy will be wasted.

 

Whether your air conditioner is energy efficient, there are still methods to save your pennies by keeping these guidelines in mind:

1. The room size matters – measurements should be quite accurate so that you can decide on the cooling capacity of the air conditioner you want to purchase. We will go into how to calculate the size of the air conditioning system for optimal cooling.
2. When the air conditioner is on, ensure that the rooms are well enclosed – meaning doors and winders should be well shut.
3. Utilize the ‘economy mode’ of your air conditioner if there is such an option, or set a timer if necessary.
4. It is always better to be patient and wait for the room to climatise than to set a higher temperature (than the desired degree) to cool down and readjust the temperature later on.

It is critical that the air conditioning systems are regularly serviced so as to maximize the air conditioner’s efficiency and lifespan. This would prevent and reduce the risk of breaking down and having to replace costly components.

 

BTUs (British Thermal Units) is the most common capacity rating on air conditioners. 1 BTU is the amount of heat energy required to upped the temperature of 1 pound (0.45 kilograms) of water one degree Fahrenheit (0.56 degrees Celsius). Thus 1 BTU is equivalent to 1,055 joules. 1 ton is then equivalent to 12,000 BTUs in terms of heat energy transfer.
A standard window air conditioner’s rating would be at 10,000 BTUs. As a comparison a standard typical 2,000 sqft (185.8 sqm) apartment will require a 5-ton (60,000-BTUs) air conditioning system. This works out to be around 30 BTUs/sqft. This is just an approximation and to get an accurate calculation, a specialist like an HVAC vendor will be able to provide this figure.

The energy efficiency rating (EER) of an air conditioner is based on this formula – BTU rating/ wattage. As an example, if a 10,000-Btu air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 Btu/1,200 watts). To be most cost effective, the EER would be as high as possible. Do note, usually, the higher the EER, the higher the price.

Let’s do a simple calculation on 2 different air-conditioner units with different EER to see which is more cost effective.

For 2 units of 10,000 BTUs, 1 has EER of 8.3, with usage of 1,200 watts, and the other EER of 10, and usage of 1,000 watts. The air-conditioner price difference is $100 between the 2.

Estimating that your usage of the air-conditioner will be 6 hours/day, 4 mths/year (cost of $0.10/kWh). The difference in energy usage will be 200watts between the 2 air-conditioner units.

Basing on 30 days in a month, your air-conditioner is operating as follows:
  4 months x 30 days per month x 6 hours per day = 720 hours
  [(720 hours x 200 watts) / (1000 watts/kilowatt)] x $0.10/kilowatt hours = $14.40.

The more expensive air-conditioning unit costs $100 more for you to buy will cost you less operating cost. In this case study, it'll take 7 years for the higher priced unit to break even.

 

Many consumers purchase an air conditioner that is larger than required as they think the bigger the better to cool the apartment. But the fact is an oversized air conditioner is more ineffective and loses energy as well. The functions of air conditioners are to take away heat and humidity in the enclosure. If the air conditioning system is too big, the apartment will be cold quickly but not much of the humidity is removed simultaneously. This results in a cold, wet atmosphere in the room. A properly sized air conditioning system takes away the humidity from the air as effectively as it chills the room.

To figure out which size unit is best for your cooling needs:
How to calculate the size of the airconditioner based on your room size:

Establish the area (in sqft) based on the equations below:

• For square and rectangular enclosure: Length multiply Width (L x W)
• For a triangular area: Length multiply Width, then divide by two ((L x W)/2)

For irregular shaped rooms, you can cut it into basic shapes to get the area using the above formulas.

But if you are still not able to decide the shape, you should seek help from the airconditioner system sales team so to get the area.
After you have determined the area in sqft, the chart below will be useful for you to decide on the cooling capacity, that is in BTUs per hour.BTUs = British Thermal Units
As every room condition is different, following scenarios should be taken into consideration to fine-tuning the sizing calculation:

• Capacity should be reduced by up to 10% should the room is well shaded.
• Capacity should be upped by 10% if the room gets a lot of the sunlight.
• Capacity should be upped by 600BTUs for each additional occupant of the room if more than 2 people inhabit the room.
• The capacity should be upped by 4,000 BTUs if the air conditioner is installed in the kitchen.
• Take into account the location of the installation of the air conditioner. If it is located in a corner of the room, the unit should be able to maneuver the air to the right way to maximize the cooling effort.
• A standard bedroom is 12 square meters (4m x 3m) and in a warm country the usual capacity for such an air conditioner unit in this room will be 9,000 BTU. The living and dining room locations will normally need a bigger capacity unit (18,000 or 24,000 BTUs)

  

The following information is provided solely for your knowledge. We do not recommend you do your own repair work as air conditioning systems require trained professionals to handle repair and maintenance issues. However we are sharing the below so you can know your air conditioner system better. Should you decide to follow the steps below, Aircon.guru will not be in anyway responsible for any injury to any being or damage to anything.
Air conditioning systems generally have 2 separate portions, which are the condenser and the evaporator. The condenser unit is normally placed outside the house on a level ground like a concrete slab. The evaporator coil is hung above the furnace.
These are the typical cases where the air conditioning system does not work:

1. When the air conditioner works but the apartment is not cold, the problem is probably in the distribution system.
2. As these 2 portions, evaporator and condenser are enclosed, you should engage a professional servicer to come and inspect for any issues or maintenance. However you still can follow these guidelines to maintain your system at the optimal condition for best performance.

Warning – Power to the air conditioner must be switched off before any work is to proceed.

Cleaning of the Evaporator
The evaporator might be a sealed unit thus it may not be easily accessible for cleaning or other purpose. However if it is accessible, the following cleaning process is the usually performed:

1. Take away the foil or the plates covering the system.
2. Clean under the evaporator with hard bristles. A small mirror maybe required to help with the viewing of the underside. Be careful not to bend the pipes connected to the evaporator.
3. Clean the container under the evaporator that holds the water that has condensed from the unit. If the days have been humid, the drain and pan should be checked regularly as if there is too much liquid the drainage system maybe clogged.
4. Put back the condenser unit and replace the foil and the plate.
5. Turn on the air conditioner to check for air leaks. A masking tape can be used to cover up the hole.

Maintaining the Condenser
As the condenser is usually placed outside of the apartment in most of the air conditioning systems, dirt, dust and other unwanted things get stuck on it. The condenser should be maintained by cleaning the fan inside, so as to maximize the cooling effect. The typical maintenance steps are as per outlined below:

1. Remove any vegetation if any has grown around the condenser unit as this is blocking the air movement.
2. Using a coil cleaner that can be purchased at hardware stores or refrigerator supply stores to clean the condenser. The instructions on the cleaner should be followed carefully. The condenser should be left to dry after flushing the coil clean. Do not hose down the condenser.
3. Use soft bristles to take away the dirt stuck around the condenser fins. However do not use a hose to try to clear the fins as the water can make the dirt into mud and these will stick to the fins. It is recommended to use a fin comb if necessary. Fins are delicate so be sure to be gentle in this step.
4. It is important that the ground the condenser is sitting on is even. The surface should be flattened if it is uneven.
5. If the air conditioner is used in a location where there are different seasons, be sure that the condenser unit is well covered to prevent damage from the weather such as fallen leaves which will block the air flow or ice forming that will damage the unit during the different seasons. You can purchase a condenser cover from the stores or just use a heavy sheet with strong cords to secure the unit.

Handling of the Refrigerant
The refrigerant for cooling purpose in the standard air conditioning systems is known as Freon. The amount of Freon in the air conditioner is critical for proper cooling to occur. If Freon is suspected to be the cause of the problem, always call a trained technician to assist in recharging the system. You should never try this on your own if you are not trained. One can do a visual inspection of the coolant tubes that is running from the condenser (outside) into the evaporator located inside the apartment. One major issue will be if the insulation of these lines is torn or worn from years of usage, this will reduce the cooling effect of the apartment. You can experiment to replace these damaged coolant line, by following the manufacturer’s installation instruction.

Troubleshooting of Window Air Conditioning System
Window airconditioners are individual units set up in rooms to cool the enclosure.
Dirt and dust is the major maintenance issue for this kind of airconditioning system. These particles reduce the efficiency of the evaporator, disrupt the airflow of cooled air into the room, get stuck in filters and block drainage system.
Several advantages of this system is that minor repairs can be performed by the owner, and that if any big repairs are required, you can always take this air conditioner out of the mounting and bring it to the repair shop yourself to save on cost. Another advantage is that this being a small unit, it can be removed and stored if no longer in use or easily covered up to protect it from external elements. One example would be during winter, air conditioners would not be required for use.

Warning: Always unplug before performing any work on a window air conditioner, or any air conditioner for that matter. This kind of air conditioner has 1 or 2 capacitors and they store electricity even with the power source switched off. Thus, always switch off, unplug the air conditioner, and discharge the capacitor by following strictly the manufacturer’s manual otherwise one may receive a severe shock. If in doubt, always engage a trained professional to do the job.


Maintaining Key Components
Regular maintenance of major parts of the air conditioner can extend the lifespan of the air conditioner system and prevent bigger problems. Here are some guidelines.Note: Aircon.guru is not responsible for any damage to any equipment or injury to any being should you decide to perform such checks yourself.

Filter
The filter should be cleaned or replace every month, especially in Singapore where the air conditioner is used often. In dusty places, this should be done more frequently. Some air conditioners contain a reusable and washable filter. This filter should be cleaned with a diluted cleaning detergent solution and rinse well after cleaning. The filter should be dry before putting it back into the air conditioner.

Power Cord
One of the issues that the air conditioner will not start up is when the power cord is worn out and thus unable to start up the unit. This power cord links the air conditioner to the wall outlet. A professional should be able to check the functionality of the cord with test wires and a volt-ohm-millammeter (VOM). A reading of ‘0’ means the cord is working; any number higher, the cord is no longer functioning and needs to be replaced.

Evaporator and Condenser Coils
Just like the filter, these parts needs to be clean every month, and more often if the location is dusty. A vacuum cleaner usually can do the job. A fin comb can assist in getting rid of the dirt in between the fins on the coil.

Switch
Behind the control panel lays the selector switch which is responsible to turn on the air conditioner.
If the air conditioner is getting power with the switch turned off, it means the switch is faulty. The typical reasons are that the insulation of the switch terminals maybe burnt. You should engage a professional to change the switch if there are burnt marks on the switch terminals.
The thermostat and the drain ports are critical especially for the window air conditioning unit. The guidelines as follow:

Thermostat
Behind the control panel lays the thermostat. This is how it is tested and/or replaced if it is faulty.

1. Take out the grille and control panel from the air conditioning system. The thermostat has a sensor attached, and this sensor is extended into the evaporator coil area. The function of this sensor is to react to temperature changes, which is controlled by the thermostat.
2. Delicately remove the thermostat and remember its location.
3. Test the thermostat with VOM to ensure it is functioning.

It is important to note the above is for a simple thermostat. If there is 2 or more lead wires connection, a professional should be engaged.

Drain Ports
Drain ports are an opening where the condensation of the water from the evaporator coil collects.
Drain ports can easily be filled with dirt and this can cause water to drip from the air conditioner. Thus it is important to ensure the drain ports be unclogged for the best performance. You can use a piece of wire or a small knife to clean the ports. This should be done every month or more frequently depending on the environment.

Fan
When a fan malfunctions, the problem is usually loose or dirty blades. If the fan won't operate or if it's noisy, cleaning and tightening will usually fix it. Here's how to repair a room air conditioner's fan:

1. Open the air conditioner and find the fan
2. Clean the fan with vacuum and cloth
3. Inspect the fan blade on the motor shaft to see if any blade is loose. If there is, tighten it. Vibration can usually loosen the bolts and nuts.
4. If the fan has oil ports, put a few drops of 20-weight motor oil to each oil port every month.
5. To test if the fan motor is spoilt, use the VOM set. If VOM is reading between 3 and 30 ohms, the motor is working well. A reading of 0 or extremely high, the fan motor is faulty and needs to be changed. A professional should be engaged to replace this motor.

Motor and Compressor
This should be checked by a professionally trained air-conditioner servicer.

 

One of the usual suspects in air-conditioning issues is incorrect usage of the air-conditioning system.
For the air-conditioning system to be working effectively, make sure the apartment’s windows and outside doors are well closed. For room air-conditioners, isolate the room or a group rooms that are linked as much as you can from the rest of the apartment.
Other usual problems with installed air-conditioners come from improper installation, poor servicing process, and lack of regular servicing.
Air-conditioner systems are normally built to high standards. We recommend you to do the first round of checking if your air conditioner fails. You should check for any fuses or circuit breakers. Do let the unit chill down for up to 5 mins before resetting the breakers.

Refrigerant Leaks
Refrigerant leaks is damaging to the environment thus one should be aware of such an issue.
Undercharging of refrigerant during installation or if there is leakage can cause your air conditioner to be low on refrigerant.
You should call the air condition technician to fix such an issue, as they will check, fix, test and then add the refrigerant chemical to the correct level. It is crucial that the refrigerant charge is as per the manufacturer’s recommendation in the specification. Not more, not less.

Inadequate Maintenance
The compressor and fan will suffer if the filters and coils of the air conditioner become filthy. This will result in the compressor or fans to live out their lifespan prematurely.

Electric Control Failure
Wear and tear is a common issue and this can happen to the compressor and fan controls, especially when the air conditioner is switched on and off regularly. Wires and terminals can corrode as well, thus all connections and contacts should be checked during a routine servicing.

Sensor Problems
Room air conditioners consist of a thermostat sensor that measures the air temperature that is blowing to the evaporator. However if the sensor is dislocated, the cycle of heat dissipation could be disrupted. The sensor should be positioned near the coil but not in contact with it.

Drainage Problems
Drainage of the evaporated water is critical. When humidity is high outside of the apartment, it is important to ensure that the drain is not congested and water can flow through.

  

• If cost is your first concern – choose the fan instead of the airconditioner.
• Well ventilated apartment (by opening the windows and doors to create a criss-cross breeze) helps to cool the apartment.
• Invest in an energy-efficient window covering that allow natural light to come into the room while minimizing the solar heat absorption.
• If the heat is strangling you and you must have the airconditioner, you can try to minimize the usage. For example you can cool the room before you go to sleep for 1-2 hours, then off the airconditioner and use the fan instead while you are sleeping.
• Recommended temperature is at a comfortable 25degC. Each degree higher, the more you have to pay as the cooler it is, the more energy is utilized.
• All electrical appliances should be switched off instead of putting on standby mode.
• Own energy labeled appliance, as the more ticks, the better energy saving properties it has.