Lots of things to defeat good A/C.
To decide whether one has good A/C get a digital thermometer and place it in the center duct. Set the blower to max and drive a couple miles at 50mph.
Good A/C starts at duct temperatures about 40 degrees below ambient in this test. Now try the test at low blower speed. It will quickly be evident why I choose high speed. Any A/C worth being called A/C will cycle the compressor under these conditions at low blow. Even on the hottest days.
So, now take your experience. You are judging A/C on a 56 deg day. Well the system should cycle before you get out of the parking lot. No way to test as the cycling point is probably 40-45 degrees. So if you did my test and the A/C was working you would only get 10-15 degrees off Ambient. On the 80 degree day you still couldn't be sure as minimal A/C (40 degree drop) will get you to the cycle point.
Now if its 100 out and you only get 40 degrees off of ambient duct temp will be 60 and there will be no cycling as the A/C is not getting to that point. To determine the cycling point at that point one can reduce the blower speed to "Min". Decent A/C will cycle at low blow during my test.
If you use a digital thermometer for this testing the cycling will be easily viewed as a rise and fall of center duct temps by about 2-5 degrees F. other thermometers aren't fast enough to view this.
Bosch Master, ASE Master, L1
33 years MB technician