If the mpg calcs from running the car from one full tank to another show an acceptable performance then you are ok.
I had a surprise with my ivtec Jazz where the aircon was on when it looked as though it was off. I had run it through the winter like this, so it was not obvious to me that the aircon was cooling until the first hot day about a three weeks ago.
This version has around LCD display about 50mm dia showing the temperature in the upper part of the display, the fan behaviour in the low part and across the middle it shows the state of the aircon ie...
A/C On
A/C Off
Blank
When showing blank, the A/C is ON. This caused dreadful fuel efficiency results but now that I habitually set it to A/C Off, the performance is much better.