After a dust storm.

A haboob is a wall of dust that can be thousands of feet high, and it has to land somewhere. A fair amount of it lands in the condenser coil on the side of your house, which is a device specifically designed to pull outdoor air through itself.

Nothing dramatic happens that night. The damage is cumulative and quiet.

The morning after

Look through the fins. Stand next to the outdoor unit in daylight and look at the coil at an angle. Clean fins read as a grid you can see through. Loaded fins read as grey felt.

Clear what blew up against it. Bags, palm fronds, tumbleweed, patio cushions. The unit rejects heat sideways and upward and cannot do it into an obstruction.

Look inside the cabinet if the top grille lets you. Storms deposit a surprising amount of gravel and plant matter inside, and loose debris near the fan is worth dealing with before it reaches the blades.

Check the filter indoors. A storm with the system running will load a filter in a single day. If you cannot see light through it, change it.

Listen for new noises. Gravel in the cabinet is the usual cause of a new rattle after a storm. The noises guide covers what each sound means.

Rinsing it yourself

Worth doing, with two rules.

Kill the power first at the disconnect beside the unit. Not the thermostat, the disconnect.

Use a hose, not a pressure washer. The fins are soft aluminium and a pressure washer folds them flat, which permanently reduces airflow through that section. Gentle water, ideally from the inside pushing out.

Where a hose stops working

A rinse moves surface dust. What a Valley storm leaves behind works into the fin pack and, after a few cooling cycles with condensation on it, sets. At that point water runs over the top of it.

That is what the chemical clean is for, and it is the difference between a coil that looks cleaner and one that works again. On the price list as its own line, and cheaper added to a tune-up than bought alone.

Why this is worth your attention

A fouled coil does not announce itself. Head pressure climbs, the compressor works harder for the same cooling, run times stretch, and the house is slightly less comfortable than last year while the bill is slightly higher. Nobody connects the two.

Then on the hottest afternoon of the year the system trips on high pressure, and it looks like a sudden failure. It was not sudden.