Your system is in the attic. Here is what that costs you.

Air handler and ducts, both in the attic

The commonest arrangement in this housing stock and the hardest one to get good performance out of, for a simple reason: a Texas attic in August is far hotter than the outdoor air, and every part of your cooling system is sitting in it.

• Supply ducts gain heat through their insulation on the way to the room, so the air arrives warmer than it left.
• Return-side leaks are the expensive ones. A leaking return pulls superheated attic air straight into the system and you pay to cool it, every hour it runs.
• The cabinet itself gains heat, and the blower motor adds its own.
• Condensate is produced up there and has to get down, which is why the pan, the trap, the secondary pan and the float switch all matter more here than anywhere else.

None of this means the system is wrong. It means the ductwork and the sealing matter more than the equipment badge, and almost every quote you receive will be about the equipment badge.

Ducts in the attic, air handler elsewhere

Better than having everything up there, and still the ductwork is where most of the loss happens. The air handler in a closet or garage is easier to service, easier to keep clean, and its condensate has a shorter and more forgiving route.

• The supply and return runs are still in the heat, so leakage and insulation still decide what reaches the room.
• Where the ducts leave the equipment matters — the plenum connections and the first few feet are where most leakage is found and they are usually accessible.
• A garage air handler brings its own question: the garage is not conditioned space either, and if the return is drawing from it, that is worth looking at for more reasons than efficiency.

The good news is that in this arrangement most of the fixable things are reachable without crawling the whole attic.

Nothing in the attic

The best arrangement there is, and rarer here than people assume — worth confirming rather than assuming, because “the unit is in the closet” frequently means the unit is in the closet and every duct is in the attic.

If it is genuinely all in conditioned space, then attic heat is not your problem and the usual suspects apply instead: sizing, airflow, charge, a blocked coil, and duct runs that were never balanced. Most of this page does not apply to you, which is worth knowing before somebody sells you attic work.

What still matters: the condensate route, wherever it runs, and whether the return is drawing from anywhere it should not be.

Upstairs unusable in the afternoon

The most common complaint in this market and the one most often answered with a bigger system. Heat rises, the upper floor sits under a roof, and in a two-storey house the afternoon sun does the rest.

Before anybody prices equipment, the questions are: how much air is actually arriving at those registers, what the return path looks like when the bedroom doors are shut, and what the ducts are losing on the way. All three are measurable in under an hour.

Summer bills that do not make sense

Worth separating into two questions: is the system working harder than it should, or is it working the right amount for a house that is losing what it produces?

The measurable causes are a dirty condenser coil, low charge from a leak, a system short-cycling because it is oversized, a heat pump running on auxiliary heat when it should not be, and duct leakage. Only the last of those is specific to the attic, and it is also the one nobody checks.

A water stain on a ceiling

Condensate, in nearly every case, and the four usual causes are a blocked primary drain, a dry or missing trap, a corroded pan, and a secondary pan that has been quietly catching water for a season and has now filled.

The float switch is the part worth asking about. It exists to shut the system down before water reaches a ceiling. A stain often means there was not one, or it was never wired, or somebody bypassed it to keep the cooling running — which is exactly how a small job becomes a ceiling.

A musty smell when it starts

Growth on a permanently damp evaporator coil and in the drain pan. Common in this climate, and it is what a coil does when it cools in short bursts and never dries out.

Two things make it worse up there: a system that short-cycles, because the coil stays wet and never dries, and return-side leakage, which is pulling dusty attic air across that wet coil continuously. We make no health claims — we will tell you what is on the coil and what it costs to clean it properly, and leave anything medical to a doctor.

It runs constantly and never gets there

On the hottest afternoons of a Texas summer a correctly sized system running continuously is normal and is not a fault — that is what design conditions mean. The question is whether it is also happening on an ordinary day.

If it is, the candidates are charge, a blocked condenser coil, airflow, duct leakage, and a system that is genuinely undersized for what the house became after somebody enclosed a patio or finished a bonus room. Measuring separates them; guessing buys equipment.