Whenever I push my defroster button my engine chokes and stops.

Any Ideas why this happens?

Thanks

Either your engine runs so poorly, or lean, that the additional load on the alternator bogs it down to a stop. Or more logically, one of the wires going to the glass is torn, or has its insulation worn off, and is shorting to the chassis. If the computer or some other component is on the same fuse or fusable-link, this might make sense.
The wires to the glass tear where they pass through the plastic trunk liner.