I'm sorry to doubt you, but I do not believe that (even with the doors of the a/c OPEN, that you sat on the tarmac for 3 hrs without any sort of air. You may have sat at the gate for that long, but I'm certain there was air. If you did sit on the tarmac that long, what was the reason they could (or would) not return to the gate?
If you are still upset, sure, write HP. You may get a voucher or something for $50.