Barely anything is coming out of the vents.

Weak airflow matters more than it feels like it should. It is not just a comfort complaint. Starved airflow across the evaporator coil is one of the two things that freezes a coil, and a frozen coil is the cheap route to an expensive compressor repair.

So this is worth chasing.

Weak everywhere, or weak in one place

Separate these first, because the causes do not overlap.

Weak at every vent points at the whole system: filter, blower, or static pressure.

Weak at one or two vents points at the duct serving them, and the one room guide covers that.

The ten minute checks

The filter. Hold it to a light. If you cannot see through it, it has been strangling the system for a while. Also check it is the right size and seated properly, because air that goes around a filter takes dirt straight to the coil.

The filter rating. A very dense filter in a system not designed for it chokes airflow by design. The MERV guide covers why the highest number is often the wrong choice.

Closed or blocked vents. All supply registers open, including the spare room. Nothing standing on a floor register.

The return. Furniture against a return grille does more damage than people expect, because return is half the system.

Then the blower

The blower motor drives a wheel with a lot of small curved blades, and those blades load up with dust. A caked wheel still spins and moves a fraction of the air it should. It is invisible unless somebody takes the cover off.

A failing blower capacitor gives a motor that runs slow or starts unreliably, which reads as weak airflow that comes and goes.

Then static pressure

This is the measurement that settles it. Static pressure across the system is the HVAC equivalent of blood pressure: it tells you whether the blower is fighting something.

High static with a clean filter means a restriction somewhere else: undersized return, crushed duct, a coil that is dirty on the inside, or a system that was never ducted properly for its tonnage.

Guessing at this without measuring is how people end up replacing a blower motor that was fine.

The ones that are not fixable with parts

Undersized return ducting and too few returns for the house are design problems. They are common in older Valley homes that have had a system upgraded without the duct being touched.

Nothing is broken, and no replacement part changes it. Worth knowing before you spend, because the fix is duct work, which is off the list here and goes to a licensed Arizona contractor.