Why would the air conditioner light come on as the engine idles and rev as if the air conditioner is working but blow only room temperature air?

May be a vacume hose leak.

Mine starts on regular AC. mode then from an Idle like at a red light it will switch over to "re-circulate"mode and start blowing warm air. While still showing in normal AC. mode. After I pull out and step on it it reverts to normal operation, and cools down. I