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Engine stalls when A/c is on

I have a 2007 ford fiesta classic (petrol) manual transmission. The car stalls when A/c is on mainly when slowing dow or down shifting from 4-3 or 2-1 ,the rpm drops or i don’t know why. and some time when A/c is on the engine starts vibrating very roughly ,when i turn off the engine and the turn it back on it goes back to normal. All these problems happen only when A/c is on.
Please help

A likely cause is carbon buildup on the throttle bore which isn’t difficult to clean. There are products made somewhat specifically for that purpose.

A less likely cause would be a fault in the system that is supposed to trigger the rpm to rise at idle when AC is on. Another less likely cause would be a failing compressor. And another could be a faulty compressor switch.

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