funny aircon

[Hocky]

Lately, my 1994 Euro C180's aircon seems to be blowing harder when I am accelerating and does not when I am cruising along. I can only presume that it is still blowing during these times, but not as hard. Is this really normal or is it due for service or what? A couple of months ago it did not do this. I thought that it would only do this if the aircon control switch is turned to no. 1 or 2. From no.2 or no.3 and above, it should not be following the engine's speed.