What is wrong with my A/C?

Question

i have a 1998 nissan sentra. i just replaced the ac compressor and the receiver dryer.
the compressor was making a loud knocking noise, that is why i replaced it.
before i changed it out my ac would blow pretty cold when i was driving but as soon as i stopped at a light it would stop blowing cold.
after i replaced it the ac blew very cold for a week or two and now it gets warm when i stop the car again.
i put about 16 ounces of synthetic freon in it when i changed the compressor.
i paid a lot more for the synthetic because it is supposed to blow 20% cooler than the regular freon.
i think the recommended is 19 oz so i may need to add a little more. or maybe i need to replace the condensor?

my question is, why does my ac stop blowing cold when im not giving my car gas?!?!

i live in Phoenix AZ. it is 116 degrees everyday, no exaggeration. so this really sucks.

Answer 1

Check your A/C cooling fan. It should be located in the front of the vehicle behind the radiator. On that model, there may be one cooling fan for the radiator and A/C or there may be a separate one for each.

When you are moving, air is flowing through the condenser, and the A/c will cool. When you are stopped, you need the fan to keep the airflow going. If the fan is not working, your A/C will not cool properly. This may have been the cause of the original compressor failure!

Answer 2

when system pressure is too high, it can cause that problem. these types of systems are very easy to overcharge... for about 80 to 100 buck, you could get it professionally evacuated an re-charged. also, DIY methods can easily overcharge and introduce air into the system....