Chrysler Repair: AC problems, hot to cold, temperature drop

Question
My daughter has a 2000 concord and is having problems with the ac. The problem is that when the car is cold, like sitting under the carport over night, the ac works just fine on the way to work. The out put air appears to be what you could expect around 40 to 45. But she goes to work and lets the car sit in the sun and gets hot..on the way home it does not put out cold air....mostly normal outside air with just a hint of coolness. The car is dark colored but this has not been happening but a couple of weeks. Then it was normal both to and from work.
I thought it may be the vent doors, and may be, but you can hear them close with a click when turned from cold to hot or hot to cold.
What would be the first thing to look for? I have gauges and other tools since I have replaced the ac on my car but this has be scratching my head.

Answer
Hi Landon,
The temperature drop (which is related to the internal system pressures) may just be too slight due to low refrigerant level in the system. It would of course be qualitatively more noticeable in the afternoon than when the air is already cooler in the morning. That would be there first thing I would check: does the system need additional refrigerant?
Roland