Both my heater & A/C are not blowing hot/cold when I'm at idel at stop lights, ect. At speed they blow hot/cold just fine. However at idel the temp. seems to drop or rise to the outside temp. & thats what blows through the vents. Last April I had my A/C serviced, recharged the whole bit... so I assume it should be in good shape. Anyone have an idea what may be causing this problem? Thx