I have the
NHB civic (5 door) and have no problem with my air con. In fact I find if I set it much below 18 after 10 mins or so I have to turn it up a little as it blows icy cold. It does get cold in the back of the car as well, as I've had my kids complaining that they are cold.
Its normally set at fan speed 1 most of the time.
Did you mean that you had it set at 21?