AIR CONDITIONING

How your air conditioning unit works:

Your air conditioner is designed to automatically remove unwanted heat from your home. Understanding and caring for your unit ensures a longer life, maximum efficiency and saves repair or replacement costs.
 
Basic split system units are comprised of an evaporator coil, a condensing unit, and refrigerant lines. These parts work with the fan and control system in the air handler to cool your home.
 
The cooling cycle starts when the thermostat senses that the home’s air temperature is above the thermostat set point. Contacts in the thermostat are closed and control voltage (24 vac) is supplied to the air handler control board. This causes the blower on the air handler to start.
 
The air handler control board then supplies control voltage to the outdoor part of the system, called the condensing unit. This control voltage causes a device called a contactor to close its contacts. This supplies power to a fan and to a pump that is referred to as a compressor.
 
This pump raises the pressure and temperature of the refrigerant gas in the system. This high temperature and high pressure refrigerant passes through the outdoor coil. This coil (called the condenser coil) works the same way as the radiator on a car but it uses refrigerant instead of water. In the condenser, this high pressure refrigerant is cooled and condenses from a gas to a liquid. It is usually cooled to a temperature about 20 degrees below the saturation temperature and is called sub cooling.
 
This high pressure/low temperature liquid refrigerant is pumped to the indoor section of the system. Then the refrigerant passes through a metering device which regulates the flow to the evaporator coil. In smaller and older systems this device consisted of small copper tubes called capillary tubes which lowered the flow and pressure. Others use specialised flow restrictor devices. Modern high efficiency systems use a device called a thermostatic expansion valve. This device senses the refrigerant temperature at the outlet of the evaporator and automatically adjusts a valve to regulate refrigerant flow.
 
These devices cause the refrigerant pressure to go down. Air is circulated over and through the evaporator coil by the fan on the furnace/air handler. Heat from the home’s air is transferred to the refrigerant. This heat raises the temperature of the refrigerant above the saturation point and it changes back into a gas. The flow of refrigerant is regulated so that extra heat is added above the saturation temperature. This is called superheat and is added to ensure that the refrigerant stays in the form of a gas as it goes through the compressor. This refrigerant gas is then pumped back to the condenser where the process repeats itself over and over.
 
When the thermostat senses that the home’s temperature is below the set point, the contacts are opened and control voltage is no longer supplied to the furnace or the air conditioner.
 
The size of an air conditioner is expressed as tons of cooling capacity. A ton is equal to the ability of the system to remove 12000 btu of heat per hour. Btu stands for British Thermal Unit and is a standard measure of heat.
 
The relative measurement of a unit’s energy use to perform this cooling is its SEER rating. SEER stands for Seasonal Energy Efficiency Ratio and is a ratio of the cooling output divided by the power input. In general terms, the higher a unit’s SEER number, the less electricity it requires to produce the rated amount of cooling.
 

 

Higher efficiency air conditioning units:

Higher efficiency units typically have some special features. They usually have two stages (speeds) of operation. In some cases this is accomplished by having two compressors in the unit. One is run on low speed and both are energised for high speed. In other cases, this is achieved by having one compressor with two motors inside. One motor is energised for low speed and the other is energised for high speed operation. On some high efficiency units the condenser fan motor can operate in low or high speed too.
 
The highest efficiency air conditioner uses an advanced compressor called an inverter drive. This compressor has a motor that runs on direct current (DC) instead of the normal alternating current (AC). This DC power can be easily varied to provide almost an endless number of speeds. This allows the unit to precisely match the cooling requirements of the home and can save a lot of energy.
 
 

Air conditioning troubleshooting

If your air conditioning problem is that the unit is not working at all:

• Check the thermostat very carefully to ensure it is turned on (a common mistake!)
• If your thermostat is a wall mounted digital type and it is totally blank, check that the batteries are not dead.
• Ensure the thermostat is turned to ‘cool’.

If the problem isn't the thermostat or remote, check the breaker.

• Check that the unit has not simply been turned off.
• Before you turn it on, make sure no one is working on the circuit that breaker supplies.
• When you've determined it is safe, turn the breaker on.
• If the air conditioner runs, cools, and keeps running, you've solved your air conditioning problem.
• If the breaker is in the middle, tripped position, turn it all the way off.
• After checking no one is working on any equipment in the circuit, turn the breaker on and see if the a/c will run.
• If it runs, cools, and stays on, make sure that the indoor and outdoor fans are running, and make sure the evaporator (indoor) and condenser (outdoor) coils are not dirty or blocked.
• Listen to the compressor for several minutes.
• If you hear the compressor starting and stopping but the condenser fan seems to be running normally, turn off the unit and have someone check the compressor. It may need new start components.
• If your breaker trips again after running several hours or even a couple of days, you may have an intermittent air conditioning problem that you should have a professional technician check.

 
The possible problems include:

• a worn breaker
• a loose, dirty, or corroded wire connection
• pitted contactor contacts
• condenser fan overheating and stopping
• wires grounding or shorting out
• compressor winding failing
• fan motor winding failing

If your breaker trips instantly as soon as you try to turn it on, stop and have a professional technician check your unit. Possible causes of this issue are direct short or ground in the wiring, compressor windings or fan windings, or a direct short or ground in relay, contactor, or transformer windings.
 
One reason not to keep resetting a breaker that trips instantly is that the shorted or grounded wiring could be sparking when you reset the breaker, and it could be a fire hazard.
 
Here are some examples of additional air conditioning problems that could be caused by repeated
 
The problem may be that your air conditioning unit just doesn't seem to be cooling as well as it should.

• Check the indoor air handling unit.
• Make sure the filter is clean.
• Make sure the coil is clean.
• Make sure the blower is clean and running.
• Make sure nothing is blocking the air flow in and out of the indoor coil.
• Check the condensing unit.
• Make sure the coil is clean and that nothing is blocking air flow through it.
• Make sure the fan is running.

 
If the problem persists, see a professional technician.
 
If your air conditioning problem is a water leak:

• Clear the drain of the indoor air handler, using a wet/dry vacuum cleaner and vacuuming the end of the drain outside the building.
• While you have the vacuum cleaner out, open the indoor air handler and vacuum the rubbish out of the pan you'll find underneath the coil.
• If you can, take a look at the corner of the pan the drain line is attached to.
• If there is debris there, clean it out.

 
If your air conditioning unit is making a strange noise:

• If it's a humming/buzzing noise, open your unit and look for a loose panel screw, fan bracket screw, pipe clamp, piece of insulation, or even a noisy relay or contactor.
• If it's a rattling noise, again, look for something loose in or on the unit.
• If you hear your compressor making a grinding or hammering noise, it may be failing mechanically.
• If a fan is squeaking, the bearings are probably drying out and may require a professional lubrication by a technician lubricate.

 

Charging refrigerant in winter

Using your air conditioning charging station in the winter months can present its own problems. The refrigeration gas (R134a) does not flow too well if the external temperature drops. Some machines have their own on-board heaters but others rely on recovering some refrigerant from the vehicle or from a supply cylinder. One of the benefits of recovering and recycling refrigerant is the heat generated through the compressor. The charging station works exactly the same way as a vehicle: if you draw gas from a low pressure area and compress it, the low pressure side gets cold and the high pressure side gets hot. This hot high pressure liquid that comes from the recovery side gives us a benefit when charging into the car as the liquid races into the system quicker.
 

One of the drawbacks with charging liquid refrigerant into an evacuated system is that as soon as the liquid is released it wants to expand into a gas and equalise the pressure between the car and the charging station. If this takes place before the full charge has been delivered then the station effectively undercharges the car and the charge is not complete. A simple trick to rectify this is to close the red HP valve on the station or the HP coupler and start the car. The compressor on the vehicle will then pull the rest of the refrigerant into the vehicle and finish the charge. The gas charge is usually weighed in from a scale platform on a modern machine and the scale doesn't care how the refrigerant is decanted.

 

The Moisture Inside

If you find that there is a regular problem with charging, check that the vacuum pump is in good condition. The oil level and oil condition is critical. The vacuum pump oil lubricates the pump and provides the seal for the pump blades. If the oil level is too low, the seal breaks down and the high vacuum required cannot be reached. The quality of the oil is also important.

A poor vacuum can cause many problems because it does not dehydrate the system properly. Any moisture in the car’s system can be devastating, as the combination of R134a and moisture creates hydrochloric acid. This quickly saturates the filter dryer making it useless and then starts to destroy the whole system from the inside out.

With the winter months being cold and damp, moisture is very difficult to keep out of an open system, especially if the vehicle has been damaged and stored for a while. Because the system is effectively charged with refrigerant (R134a), as soon as it escapes and evaporates it leaves the inside of the system very dry. Moisture is automatically attracted to the dry areas and considerable amounts of water can form inside the pipes and condenser. This is unavoidable and only an extensive evacuation can rectify it. In this case a new filter dryer must be fitted and the system evacuated immediately. If we break into the system and have to leave it for any length of time then taping the open hose ends up with tape can be a great help. This obviously stops moisture and dust from entering the system and causing unnecessary contamination. A good vacuum gauge can be critical in determining when sufficient vacuum has been achieved to sublimate (remove) moisture.

A very cold car can be difficult to recover the gas from. This can be due to the pressure being very low in the system and warming the car up is a great help. Also, if the recovery cylinder has picked up air (remember air cannot be condensed) the pressure increases and the compressor will struggle. As a tip, it is always worth keeping the new supply cylinder near the station so that they are at the same temperature.

 

Decrease Your Refrigeration Recovery Times

In most recovery applications we are all in a hurry to recover the most amount of refrigerant in the quickest time available. This can be made easier by using the ‘Push-Pull’ method. Otherwise you must ensure that your recovery unit does have the refrigerant throttle to it via the manifold to prevent liquid slugging, which will cause damage to the compressor.

In all applications you should wherever possible have your cylinder under vacuum and as cool as possible. This will also help speed up the recovery process.

What is the Push-Pull method?
In simple terms, you draw vapour off the top of your recovery cylinder, run it through your recovery unit and then back into the system you are recovering from. Next, run a hose from the liquid dipper tube on your receiver to the liquid in your bottle.
This method is only useful when more than 7kg of liquid is known to be in the system and it can be easily isolated.

 

General maintenance for Recovery Machines:

The actual requirements on Recovery Machines are minimal but important!
 

• Keep the unit clean by wiping it down with a damp cloth to remove dirt, oils, etc. prior to storage for the day. Standard household detergent or isopropyl alcohol may be used if the unit is particularly dirty; in all cases, exercise care to prevent liquids from entering the unit. Gasoline and other solvents are to be avoided as they can damage the plastic enclosure and are hazardous.
   
• Clean inlet particle filter regularly. Discard internal filter screen if it is heavily contaminated and replace with a new screen.
   
• Ensure that the Inlet and Discharge ports are protected and kept clean by replacing the plastic caps after every use. For best results, keep a filter permanently connected to the suction line port in a similar fashion to the filter in a liquid line.
   
• Change hoses periodically as they develop leaks and a build-up of contaminants over time. Change hoses at least once per season. Especially change the little rubber gaskets inserted into the hose end fittings. If a Schrader Valve is inserted into the end hose fitting and the rubber gasket is worn, the end to end connection will almost certainly leak !!
   
• When storing the recovery machine for the season, or for long periods of time, purge the unit with an inert gas such as Nitrogen.
   
• When performance falls off it is likely that the compressor seals require replacing. This is normal with use and may occur after a year or two or more often, depending upon the conditions that are prevalent during the recovery operations.