(Dallas, TX)  —  Business is picking up at local heating and air conditioning companies with Monday’s arrival of a polar front in North Texas.  HVAC companies were reporting an average of about two-dozen calls an hour before 5 p.m.  After the end of the workday, they were flooded with calls from people who had come home to find their central heat wasn’t working.  One local contractor says he expects customers to keep him busy with heater jobs until January.