Subaru Temp rises when AC on

Thanks all. I have a 2000 Forester L. So far so good but new problem. Driving in 60ish outside temp indicator says all fine. As soon as i turn on the A/C, up we go to redline in under 1min. Turn on heater or off A/C back to normal. Tried in garage but all was okay. Both radiator fans working well. No visible coolant leak. Seems weird that alls good in normal driving but A/C on is a problem. Any thoughts? Thanks.