Car sputters when A/C is turned on

Hi I don't wanna take up any space asking questions about a non accord. I really need help with this one tho. So my brothers 94 Geo Prizm over heated and then turned off on him the other day. He let it cool down, put coolant managed to make it home. So the next day i looked at it and the radiator fan wasn't working and noticed the radiator cap was leaking coolant. I went and bought a new radiator cap as well as a new motor for the fan. It started working just fine no overheating (Fan is rigged to stay on all the time since it used to overheat before). I let the car sit for about a half hour idling and it didn't overheat or leak. Soon as i turned the A/C on the engine starts sputtering, a lot of vibration like if it wants to turn off but doesn't. The A/C blows rather warm unless i get it up to a good 30mph then it doesn't sputter and a/c blows colder but soon as i come to a stop and it idles it starts up again. A/C off it seems to run fine even tho he tells me it doesn't feel 100%. Any ideas like i said i know its non honda but im puzzled wanted to see if i can get some help from the forum.

Maybe the clutch/bearings are bad or some faulty ground wiring from the compressor?

Yea ive read maybe the compressor is giving out ima look into it.

Check for a loose drivebelt, and a loose crank pulley. My accord tended to bog and stutter and make a rattling noise with the A/C on but ran fine with it off. I figured the compressor was going bad. Then yesterday it threw the belts off the engine, and I found a loose and wobbly crank pulley. I won't be working on it until this weekend. I hope and pray that it is just a loose crank pulley bolt, because if the threads in the crank are stripped, then it's time for a new engine.

I highly doubt you could strip the splines on the crank pulley just driving accessories. The rubber ring is probably ripping itself free, we have a Hyundai Sante Fe in the shop right now with half the crank oulley on the crank and half sitting in the passenger seat

Not an uncommon failure.