I have friend whose A/C in her car is working fine when the car is in motion, but when stopped at a traffic light it gets hot. Not like just a tad warmer than when driving but actually hot. Anyone ever heard of anything like this?

BTW: It is NOT an RX-8.

Probably condensor fan isn't working. May causes by broken fan, burned fuse, or the bad relay. To find out if the condensor fan is working correctly is to pop the hood and watch if the fan is running when the AC is on. If they are running, then that car may have some other issue.

He might just need some Refrigerant. He might have a small leak

like seikx mentioned, it could be from airflow over the condenser, airflow over the evaporator (not likely though), or because the engine gets too hot underhood and the AC system can't cool the hot air. does holding the engine at a constant higher rev make a difference? what about turning on the interior blower to high?

Hopefully its not the condenser because I know that is a $600 part.

It most likey it the refrigerant ,though. Just take it to a shop and have them check it out.

At idle, the compressor is only working at about 8% of its design maximum speed - it will get a little less cold, though it IS still putting out, just not enough.

Because of the extremely high revs the engine can reach, the pulley is a little undersized for adequate idle output, it is just something you will have to live with.....
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doc