What causes the A/C clutch to spin backwards while it is engageing???

What is your question?

the a/c unit when it engages runs very short time and stops..like only 3 seconds and stops repeats cycleing..belt seems to slip backwards while shaking..

What makes this problem better or worse?

Air blows hot..

How long has your 1998 Ford Mustang had this problem?

long time...