Mitsubishi Repair: engine stalls out when heater is turned on, engine stalls, charging system

Question
what could be causing this?

Answer
Chris,
When the heater is turned on, it draws extra power from the charging system.  If the battery or alternator is weak, it can cause the engine to stall.  Also, in some cars, when the heater is on (particularly the defogger), the A/C may come on as well and that will indeed put an extra strain on the engine.  Have your mechanic inspect those areas and hopefully they'll detect the problem.
Good luck!