since my heater core leaks and its no good no more, if i put my a/c(it works) and put the a/c air on warm for some heat would it work witout the heater core leaking

 

If your heater core is leaking, why not take the time and make the effort to replace it? If the heater core is leaking... you're loosing coolant. If its dripping inside of the car, that's plain nasty. If it's leaking under the hood, the (engine) cooling system is not as effective as it should be.

A new replacement heater core will run you about $25+-. from Auto Zone.
You should replace the hoses on the firewall while you're at it. $35.+-
Three gallons of anti freeze, about $20+-.

Figure about $100. out of pocket to fix if you do it yourself.