Max A/C kills engine

What do you have for cam / timing / carburetion, and setup? EG an engine idling too lean will have very little low end power

Make sure you are not missing something IE an oddball problem like a SHORTED clutch circuit on the compressor could be drawing down electrical.

SUSPECT you might be overcharged or some other problem (metering device? IE TXV or orifice) and "slugging" the compressor. If the compressor is getting liquid, it won't be long for this world