Air conditioner [Not blowing cold]what to check

An air conditioner that runs but does not cool has a small number of explanations, and they are worth taking in order of what they cost. Start with the filter, because it is free and because it produces symptoms that look like something much more serious. The indoor unit works by pulling room air across a very cold coil. Restrict that airflow and two things happen: less air gets cooled, so the room does not cool, and the coil gets colder than it should because there is not enough warm air passing over it to keep it above freezing.

Once it ices, airflow drops further and the whole thing accelerates. So the machine ends up frozen solid and blowing almost nothing, which is why people describe this as the unit having failed rather than as a dirty filter. It gets worse than that, and this is the part worth knowing before you pay anybody. On some systems a restricted indoor coil produces readings that look like a refrigerant problem. Mitsubishi publish a code for an abnormally low pressure or temperature sensor reading and name three causes for it: a lack of refrigerant, faulty expansion valve operation, or a blocked indoor coil. Two of those are expensive certified work and one is a filter you can wash in a sink. Daikin, similarly, publish a code for high pressure control or freeze-up protection where a filthy indoor filter or blocked airflow is a legitimate cause. If the filter has not been checked, it has not been diagnosed.

After the filter, the checks run outward. The outdoor unit needs to reject the heat it has collected, so anything smothering it — a fence built too close, a shrub grown over it, a cover left on, leaves packed into the fins — reduces cooling in exactly the same way. Then the settings, which catch more people than they should: a system in fan mode or in the wrong mode will run and blow and never cool, and a heat pump air conditioner in heating mode on a warm day feels like a failure. And finally the genuine faults, which are the refrigerant circuit and the compressor, both of which are certified work and neither of which you can assess from the room.

1. 1

   Open the indoor unit’s front flap and take the filters out. They are designed to be removed without tools and this is explicitly an owner task.

2. 2

   Wash them, let them dry completely, and refit them. A filter that looks grey rather than white has been restricting airflow for a long time.

3. 3

   Check the indoor coil behind the filter for ice. If it is frozen, leave the system switched off until it has melted before judging anything else — Daikin’s instruction for a unit that has stopped itself is to clean the filters, clear anything blocking the inlets and outlets, and only then turn the breaker off and on and try again.

4. 4

   Go outside and look at the outdoor unit. Clear leaves and debris from the fins and make sure nothing is blocking the airflow around it.

5. 5

   Confirm the mode and setpoint on the remote. Cooling mode, a temperature well below the room, and fan speed on automatic.

6. 6

   If it still will not cool after the filter is clean and the coil has thawed, retrieve the fault code and call an engineer.

   Do not add refrigerant, and be wary of anyone who offers to top it up without finding a leak. The circuit is sealed — if it is low, it has leaked, and handling the gas requires certification by law.