I have a 2004 Nissan Quest, Problem--- No Heat (defrost or Cabin) when initial start up and Idle. Only when driven up to highway speeds does the heat work correctly (Then heat works great). I have replaced the thermostat(No difference). I have removed the upper heater pump which has a 12 volt motor and Magnetic drive pump and the motor runs fine and pump end works great. I am thinking that ther is a sensor and or a relay the turns the heater pump on at startup and this is not functioning, does this sounf like the problem? If not do you have any ideas??