It is known, to get the coldest temperature out of the vents you must operate the blower at the lowest speed. The heat will be absorbed through the evaporator making the vent temperature the coolest.
There are a few reasons your auto air conditioning may not work and this is a nasty one. The evaporator must allow air to pass through it. This auto air conditioning service involved an ac leak inspection and lead us to removing the dash of the vehicle to inspect the evaporator.
If your ac is not as cold anymore, it may be time for an inspection. Don’t just recharge and let it go!