Join Date: Jun 2006
Location: Eastern ON Canada
Car: 07 OBW 2.5i D-4AT
Feedback Score: 7 reviews
There shouldn’t be a significant increase in temperature, although I have noticed that after the car is parked in the sun, it will blow warmed air, probably because the metal around the intake area (just below the windshield) and the air in the interior space itself is hot. But this dissipates fairly quickly. In normal driving, the incoming air should be almost as cool as it is outside. (Hot coolant is always circulating through the heater core, so there will be some heat generated inside the heater housing. However, this should be minimal, and yes, if it is cool outside you should be able to cool the interior without using the A/C.)
A quick guess would be that the linkage from the temperature control to the heater is either loose or misadjusted.
Assuming that your HVAC control is manual (not automatic), then it’s a fairly simple system. The front panel temperature knob is connected by a cable (fixed outer housing, moving inner core) to a lever linkage arrangement on the driver side of the heater housing. When the control is turned, the inner part of the cable moves the first lever which then moves the next which in turn moves a “door” inside the heater housing that adjusts the path of the air, i.e., through the heater core (which is always hot), partially bypass the core (i.e., mixing some warmed air with cool air), or totally bypass the core (when the control is at the blue end). The outside housing of the cable is clamped to the side of the heater box and should not move when the control is adjusted.
If the cable is not firmly attached to the heater housing, then as the control is moved, the cable itself can move instead of the lever/door being moved.
The cable might be tightly clamped, but in the wrong position. In this case, even when the temperature control is in the full cold position, the air temperature door inside might not be. Question -- can the control be moved to the full hot position (red dot) without forcing? If not, then this could indicate maladjustment.
Finally, I recall reading elsewhere where the lever linkage itself has become disconnected, resulting in no control of the temperature.
On my '07, the action of the lever system is visible through an opening in the lower cover of the instrument panel just above the accelerator pedal. When the temperature control is in the full cold position, a white lever that the cable is connected to appears to be just above horizontal, pointing towards the front of the car (in other words, in the 10:00 o’clock position). When in the full hot setting, the white lever is down, at about the 7:00 o’clock position.
In order to see more, including the clamp, the bottom cover of the instrument panel would have to be removed.