Can 20yr AC compressor overheat the 20V?

[wadd-wadd at usa.net]

The car is a '91 CQ with a working, original AC compressor. The car has a new
radiator and properly operating cooling system (senors, fan, etc). 

With AC off, the coolant temp is about the bold line, 90-100 degrees, even if
it's 100 degrees outside. 

With AC operating, the car overheats if it's more than about 80 degrees
outside. 

I am having difficulty troubleshooting this. The cooling system is otherwise
brand new and operates normally.

Can it be the old compressor?

What're your thoughts? 

Thanks.