Hello to all

I have a small issue I have not been able to resolve with my AC here in Miami.

When I start the car in the morning the AC is a freezer and keeps very cold
till I stop the car and let it sit for a few hours till noon time.
When I start it up at lunch to go have lunch it just blows hot air but I hear and feel the compressor cycling on/off my lunch trip is just 1 mile each way
not enough driving but if I choose to drive it farther after about 5 min
it suddenly starts getting very cold.
If I go out in the evening I can start and stop it with no issues.

I have a set of guages I connected them (around 10am 95 deg outside)
and ran a fan in front of the car the low kept around 40 to 45 but the high
scared the hell out of me I used to work on Ac's back in the late 60's and 70's
with R12 this is R134 I had never seen a high climb up to 350 + (95 * 2.5 = 237 lbs) not 350 + but the best part about it was the car was very cold inside.

any of you out there who deals daily with R134 and cars what could my problem be, the only thought I have had is an over charged system
and my tell tail was chattering from the compressor.

any suggestions wil be checked out I would like to fix this issue.

By the way where and how hard is it to get to the vent door that opens and closes out side air ?

Thanks
Xavier