Help!spent so much but cant fix problem

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I have a 92 Civic DX. I have driven the car for 2 years and have never encounter this problem until i moved to Phoenix, AZ from Seattle. During daytime in AZ, especially when the temp reaches 110 deg and over, the engine tends to stall when the A/C is turned on and coming to a stop. However, if i turned the A/C off, it runs good.

This problem only happens during daytime. when night falls, the engine run smoothly with A/C on. I went to honda service center and several auto shops and spend hundreds of dollar, ending up with no results and they can't find the main problem.

The battery is okay, cause if i run the Stereo, i will not cause the car to stall. please help me