I am not an expert by any means, but there are a few issues to watch out for and although I am an inspector newb, I would like to contribute to the forum.
-many furnaces, A/Cs and heatpumps have delays. You may have to wait up to 5 minutes for them to kick on.
A Rheem A/C is an excellent brand (i put one in my own house) but the condenser will go into a 5-minute time delay if it was short-cycled, and Carrier furnaces will blow air for 90 seconds before they ignite. These settings can be adjusted by the thermostat or circuit board.
My advice is to be patient instead of automatically assuming there is an issue.
-HVAC equipment located in an attic can cause devastating damage by condensate overflowing to not only the living space below, but the basement below that if it is not equipped with a float/cutoff switch. I do not want to be the guy that did not recommend one. They should also be equipped with a cleanout in pvc condensate drain line.
-call it out if there is no filter media, or the inside of the furnace/AH is really dirty–this could indicate that the evaporator coil is plugged up with dirt/pet hair and guarantees the ductwork is filthy as well *cringe.
Easy visual cues that indicate equipment:
-metal flue = low efficiency (some codes require them in attics in certain states to avoid freezing condensate lines)
-plastic flue = high (90% or above) efficiency
-Reversing valve = heat pump
-gas line and/or flue = furnace
-big electrical wires entering the side, and the presence of breakers on the front of the air handler = electric heat
-every single AH (air handler) over 5 years old will have mold inside of the cabinet (unless it is equipped with a HEPA air filter or UV light system, etc., and likely even still will be)
-electric heat = air handler
-gas heat = furnace
*there is no such thing as an electric furnace or a gas air handler