Why doesn't my ducted air conditioning work in all rooms?

By definition a ducted air conditioner has an indoor unit that has ductwork connected to it that distributes conditioned air to the supply air grilles to blow cold air into the air conditioned spaces.

Is this a new problem?

The first question that you need to ask yourself is whether this is a new problem. In the past had your ducted air conditioning system been supplying air to all the outlets in your house and now only one outlet has no cool air - then it is most likely caused by a failed damper motor, a crushed duct or air loss.

If the supply air outlet from your air conditioning system has never had air flow it could be one of the preceding reasons has caused it since installation \ you have owned the property or there is inadequate air flow in the ducted system to provide air to that outlet.

There is a difference between low air flow and no air flow. No air flow will be caused by blocked or disconnected ductwork. Low air flow can be caused by a number of issues. Sometimes low air flow can feel like no air flow to the naked touch.

Common reasons why your ducted air conditioning is not working in all rooms

• Failed motorzied damper
  The most common reason you have air flow stop to a supply air outlet is that the damper motor that governs the air flow to that outlet has stopped working. There are a number of reasons this may have happened including:
  • failure of the motorfailure of the mechanical connection to the blade in the damperfailure of the cable connecting the motor to the zone controllerfailure of the zone controller
  The most common reason for damper failure in a ducted air conditioning system is the failure of the damper motor. These are like any motorized electronic component and are subject to failure due to wear and tear and old age.

• Crushed duct
  Your ducted air conditioning needs its duct work to be free flowing. One thing that can happen to your duct work is that it gets crushed. The most common cause of this is someone standing on it in the roof space or something in the roof space falling onto it. As long as the duct is accessible this is normally easily rectified.
• Air Loss
  A ducted system relies on the integrity of the ductwork to function effectively. When the duct work has a rupture or is disconnected cold air escapes.Cool air is like water, it will follow the path of least resistance. So if you have ductwork that is open to your ceiling space - a large portion of the air from your air conditioning system will likely be going into the ceiling space rather than out of the supply air diffuser. This then limits the amount of air coming out the supply outlets.
• Reduced air flow
  Reduced air flow from an air conditioning system that has fully functioning duct work can be caused by:
  • dirty air filters - easily fixed by removing and cleaning the filterblocked condenser coil - on an indoor unit these are capable of being cleaned, provided there is adequate roof access. However, this is not a small job, and requires some planning.
  Both of these conditions reduce the amount air flowing through the indoor units evaporator coil. If you are running multiple zones on a ducted system and you have reduced air flow it may feel at some of the vents that there is no airflow.
• Inadequate air flow
  Inadequate air flow is different to reduced air flow. Inadequate air flow is normally a function of poor initial design or installation of air conditioners.
  • Undersized system - ducted air conditioners have a rated cooling capacity and a rated air flow. For example a 12kW ducted air conditioner might have a rated air flow of 800L/s. A 300mm duct will flow 280L/s - so if you have 5 x 300mm duct connected, with a flow capacity of 1,400L/s - you will not be getting much air flow out of each vent.It is not always possible \ cost effective to install a system that has enough capacity to cool all rooms in a house at the same time. This is where zoning comes into play. A simple demonstration of effect of zoning can be had by turning off all zones but one - and you should have a lot of air gushing out that one zone. If you then turn all zones on - you will see much reduced air flow coming out the same outlet. The amount of air produced by an air conditioner is finite - the question is where do you distribute it.
  • Poor duct design - when the air conditoner installation is designed, consideration needs to be given to adequate duct sizing. The duct run should not be too long and the size of the ducting needs to be matched to the capacity of the system and the size and number of supply air outlets. If any of these elements are wrong you can end up with too much or too little air coming out of your supply air outlets.
  • Outlet at very end of long duct run - the longer the duct run and the more turns (in particular 90 degree turns) in the duct run the higher the resistance in the duct run - this is called static pressure. In broad terms the higher the static pressure, the lower the air flow you will achieve. What this effectively means if you have a large house \ long duct run - the supply air outlets at the end of the duct run will have lower air flow than the outlets at the start of the duct run.

What should you do if you a ducted air conditioner and you don't have air flow in one room?

As long as a ducted air conditioner and its ducting is accessible, all of the problems above can be rectified. At Sun City Air Conditioning we have decades of experience in air flow problems and are available to diagnose and resolve them for you.