Yes, there were & are presently blower speed setting options. Even on belt-drive single speed blower motors the wheel diameters can be changed to increase or decrease speeds within parameter limits.

To select the correct speed option you need to know how many CFM's of airflow your furnace & the AC require.

With a well sealed duct system, the static pressure readings have to be compared to the air handler's chart or graph, or direct instrument measured CFM airflow volume(s).

You have to know a number of things before you can select the correct speeed option. - udarrell

Ok I cannot find any tags on the unit but I do have some model #s . If these tell you anything then please advise: furnace GMS80453AN , coil CSCF1824N6 .

For some older air handler motors, the speed tap wires are on the motors themselves. Newer, multi-speed air handler motors have the speed taps on a circuit board near the motor. Knowing what to look for or how to read a wiring diagram would be very helpful for you.

Good luck.

Ok I found some info. My furnace is as follows:
45,000 btu
max cfm @0.5 ESP is 1200
heating speed as shipped = Medium = 2.5 tons@0.5 esp = 1048 cfm

I have a 14" return.

5 supplies:
(4) 8"
(1) 4"

Other speed options:
med-lo = 2 tons of ac = 853 cfm@0.5 esp

I did not mention this but my system is a 2 ton cooling 820 sq ft.

My blower is set on high speed for cooling does this sound right given the info above?

The best way to set the blower speed for the best efficiency is to shoot for a 20 degree F delta T

In other words, after the ac has been running at least 10 minutes so that the coils are fully loaded, measure the supply temp above the coil and the return air temp going back to blower and select a blower speed that is closest or just below 20 degrees diff.