Took it in yesterday and had the radiator flushed. When I left the heat was not working. The front and rear were blowing but it was ice cold and the middle was not blowing out any air. All three were working fine before I the flush. Called them to and told them what was going on. On the phone they explained to le about air pockets. Took it back to them and they then said sometimes when a radiator is flushed it will knock things loose and can clog the heater core. They said they went ahead and flushed the heater core so the heat in front was working. They said the rear was still cold because has more then one heater core. When I left the second time the heat in front was working and continued working for about 10 minutes before blowing ice cold air again. Took it back to them today and asked why they didn't tell me before flushing the radiator that it could cause issues and he just got a smart attitude about it. What did they do to my Navigator?