My math was a voltage drop calculator program that you can download from www.mikeholt.com.
If you want to do it the hard way.....
The formula for single phase DC voltage drop is VD= 2KIL/CM
VD= Voltage drop
K= Specific resistance for type of conductor @ 75 Deg. C. If I remember correctly it's 10.4 for copper and higher for aluminum. About 17.
I = Current in amps
CM= Circular mil area of conductor
Notice I said this formula is for DC circuits and we are dealing with AC. This formula is pretty close for most applications. AC has an added components to factor in like the type of conduit the wire is in, single phase or three phase and has a resistance known as impedance that DC does not have. It gets much more complicated so the above formula is generally as accurate as we ever need to get.
No draw back to your circuit at all.
Your unit is probably thrilled to death. Equipment like ac units are designed to operate at a fairly large range of voltage. Usually about + or - 10%.
If you were pulling near capacity of this circuit it would be advisable to increase the conductor size. Like I said voltage drop in this situation is not code mandatory. Only advised for proper operation. However, it is good engineering practice.