Davebargh

Hi, I'm having problems with my heater MY 2004 350Z. Before anyone says air in coolant system, a lot of time was spent bleeding all air out. The issue is that when control knobs are in Auto positions, the fan runs at full speed and, unless the temperature knob is turned fully clockwise the air is freezing cold from vents. If the temp knob is fully clockwise (32), the the air from vents is really hot (as it should be). One "notch" back anticlockwise the air is freezing cold again. It appears that the temperature control servo motor must be driving to coldest position at any temperature control position except fully clockwise. This also occurs when the air direction and fan controllers are not in auto mode. The fan control is OK manually. Without engine running, the temperature control servo can be heard to operate incrementally with the control knob movement. No obvious sign of damage to ribbon connecting cable. I'm wondering if the system defaults to a cold temperature setting (other than when control knob is fully clockwise), if there is an issue with either the Ambient or Cabin Air Temperature sensors? Has anyone experienced this? The manual does not give symptoms of sensor failure although I could imagine that the system may default to cold for possible safety reasons. Dave

Since replacing coolant my heater is acting strangely. Engine warmed up to normal, with both outer knobs set on auto and temp knob set at coldest, the fan motor runs full speed with AC on. Ice cold air from vents. With temp knob set half way, still freezing cold air from vents. Only when Temp setting at highest, hot air from vents. There is no temperature control in between, it's either freezing or too hot. Is there a valve operated by temp control knob that allows water into heater matrix or is it directly plumbed into coolant system?