4.9 Star Google Rating
Error Code
A5 covers two opposite conditions in one code. In heating it means the system has hit its high pressure limit. In cooling it means the indoor coil has dropped towards freezing. Both are protection trips: the unit shuts down because continuing would damage the compressor. What the code points at depends entirely on which mode the unit was in when it tripped.
In heating the indoor coil is the condenser, so anything restricting air across it pushes pressure up. A dirty filter, a closed louvre, furniture in front of the head or a duct that has come apart will all do it. The system then trips on high pressure to protect the compressor. Airflow gets checked before refrigerant.
In cooling a coil that gets too cold means not enough warm air is passing over it. Restricted return air, a failed indoor fan or a low charge will each drop coil temperature until freeze protection trips. Ice on the indoor coil is the visual confirmation. Keep the unit off while it is in that state.
A system short of refrigerant runs colder than it should in cooling and hotter than it should in heating, and both directions can end at A5. Low charge almost always means a leak rather than a slow loss over time. Topping it up without finding the leak just moves the problem forward a season.
Both coils need air. A condenser packed with leaves, pollen or pet hair cannot reject heat, and an evaporator clogged on the air side cannot absorb it. Either will push the system into a protection trip. Coil cleaning is routine maintenance that most A5 codes eventually trace back to.
The return filter comes out first, then the indoor coil is inspected for dust matting and the outdoor coil for leaves and grass. Both are cleaned before any gauges go on. It is the cheapest test on the list and it resolves a large share of A5 codes, particularly on units that have not been serviced in a few years.
Charge is checked by weight or by subcooling and superheat, not by pressure alone, because pressure readings move with outdoor temperature. If the charge is short, the next step is finding where it went. A system that needs gas every season has a leak that a pressure test will locate.
Restriction in the circuit looks similar to low charge but behaves differently. A blocked filter drier or a kinked line will show a temperature drop across the restriction. Measuring temperatures either side of the likely spots tells a technician whether this is a flow problem or a charge problem before any gas is added.
Isolating the unit for a few minutes clears the protection trip and lets the system restart, which is useful to confirm which mode it fails in. Watch what it does next: a quick trip in heating and a slow one in cooling point in different directions. The reset is diagnostic, not a repair, so do not repeat it endlessly.
