The condenser coil shown here, was completely covered with seedlings from cotton wood trees. Every spring, these seedlings can quickly cover a condenser coil. If you cleaned the coil early enough, using a brush, it will just peel off the face of the coil.
The next image shows a small window AC with the outer cover removed. The back side of the condenser coil is very dirty. Dirt that has been baked on will need to be cleaned using coil cleaner and a pressure washer. A pressure washer must be used carefully, as it can very quickly bend over the aluminum fins on the condenser coil.
Keep the spray parallel to the fins and do not get too close. Hitting the coil with high pressure water at an angle will quickly flatten the fins. Where possible, try not to push the dirt further into the coil. Use a soft bristled brush to clean off the surface of the coil, then, spray the water in the opposite direction of the air flow, to push the dirt out.
In most cases, this is not easy to do. However, spraying in a counter flow direction will prevent the large dirt particles from becoming lodged deep in the coil.
“I have seen many units that look clean on the surface, but when you look closely between the fins, there is dirt packed in tight. The dirt is very difficult to remove and also causes the unit to shut down on hot day.“
After spraying in a counter flow direction, switch to the opposite side and then try to work the rest of the dirt down and through coil.
Coil cleaners can be used to loosen dirt but be sure to completely rinse the cleaners off. Residual cleaning fluids left behind, can deteriorate the aluminum fins. If the coil is relatively clean, then just use water, it works well and is environmentally safe.
An air conditioning system works by absorbing heat from inside the building and rejecting that heat to the outside. If the heat cannot be rejected efficiently, the cooling process will slow down or even stop. Larger air conditioning systems, have a pressure safety device, that will shut down the compressor, if the pressure is high. Then, it may need to be manually reset, by cycling the power or pushing the reset button. Smaller systems, will use an internal pressure relief which is built into the compressor. The compressor operation will become very loud if this occurs or the compressor will shut off, on an internal thermal overload which should reset after several hours.