Two options.
1. It is hot outside.
2. The heat control flap is out of sync with its control.
1. On its coldest setting the air will never be cooler than outside. Yesterday where I was the outside temp reading was 23 degrees, so without aircon, that is what you'll get.
When the car is sat on a sunny day, even if in the shade, it gets hot inside, which includes the airducts under the fascia. It takes a while fro aircon to cool these before you feel the full effect of the cold air, it will take a very long time for non-aircon cars to cool these ducts to ambient, if in direct sunlight, maybe not at all. With the trend to larger blacker fascias, this is getting worse.
2. Heat control flap adjustment.
As you turn the heat control, it just moves a flap inside the heater box that allows at one end just outside air to pass and at the other only air through the heater matrix. Usually you should be able to feel this flap hitting the end of its travel as you turn the control from one end to the other. You may be able to grovel under the dash and see it moving. If you can get to it, disconnect it and see if you can move it further than the full cold had placed it at. If it is out of sync, you'd expect it the flap to hit max hot before the control did, so the control will not reach its full position. If this is the case, you should be able to adjust its position as there is usually some adjustment on the control cable. However, if it has recently moved, a new clip or cable may be required to prevent it moving again.
Try setting it to cold before the engine has been run and see what temp air comes through. Then with engine running see if it gets warmer. If it does, the flap needs adjusting. If not, you'll have to open a window, like we all used to before we got aircon.
Hope this all makes sense, ask if anything needs clarifying.
