In this valley the air handler usually lives in the garage

Almost certainly not, and a bigger one would make it worse. Cooling drops the temperature quickly, but moisture only leaves the air while the coil has been cold and wet for a sustained period. A system with more capacity than the house needs satisfies the thermostat before that happens, so you get cold, damp air. Three things to check before anybody prices equipment, all of them free or cheap: whether the thermostat fan is set to on rather than auto, because running the blower continuously re-evaporates the water off the coil and blows it back into the house; whether the filter is restricting airflow; and whether the return is leaking. In this valley those three explain most of it.

A leak on the return side of the air handler. Everything between the return grille in the house and the machine is at negative pressure while the system runs, so any gap in it draws air inward from whatever is around it. When the machine is in the garage, that means garage air is being distributed to every room. It is measurable with a manometer, usually visible with a torch, and sealing it with mastic is about a day of work. If what you can smell is exhaust rather than general garage air, treat it as urgent, ventilate the house and do not run the system until somebody has looked at it.

Almost always a blocked condensate drain rather than a broken machine. A coil running for nine months of the year produces a great deal of water and it all goes down one small pipe, which in this climate grows things. When it blocks, the pan overflows. Clearing and flushing the line is routine work; what stops it happening again is a float switch that shuts the system down before the pan overflows, which costs very little. One thing worth watching for: if you ever see water dripping from a pipe stub under an eave, that is the secondary drain doing its job and it means the primary is already blocked.

More often than the label says, and how much more depends on where you are. Nine months of running, dust from fields and roads, and in a workshop garage a good deal more than dust, all load a filter and a coil faster than a label written for a national average assumes. We set the interval after looking at your actual filter rather than from a chart, and we will tell you if the honest answer is that yours is fine as it is.

No, and we will say so plainly. What we do is find and fix the moisture source, which is our trade — a leaking return bringing in humid air, a blocked drain, a system that never runs long enough to dry the house, ductwork sweating in an attic. Testing for mould and removing it is an assessor’s and a remediation contractor’s work and in Texas that is a licensed field of its own. We also do not do commercial refrigeration — cold rooms, coolers and freezers are a different trade.

Edinburg, McAllen, Pharr, Mission, San Juan, Alamo, Weslaco and Donna.