Why does the car shut off when I turn the heat.

This happens because the air conditioner compressor is locked up. It comes on when you turn the heater on which is normal. Just remove the wire from the clutch as you will be fine or replace the compressor here sia guide to help you see what you are in for when doing the job.

https://www.2carpros.com/articles/replace-air-conditioner-compressor

Please let us know if you need anything else to get the problem fixed.

Cheers