Nissan Sentra - Air conditioning only works in 4 position

Hi,

My Nissan Sentra GXE - 2001 - 154.000 kms has a problem with the air conditioning.

It only works (heater and cold) when the control switch is in number 4. I mean, when I change the Switch form OFF to 1, 2 or 3, I can heard the click but not air si coming out from the air, but when I select the position 4, everything works fine. I already change the control and it is still the same, so I think the problem should eb a relay or something like thst.

Any light on what do I have to do?

Thanks

Carlos