2000 Accord A/C problem

Hello,

I have a 2000 Accord LX. The A/C no longer blows out cold air, though,
when I turn it on, I do hear something under the hood kick on.
Occasionally, if the A/C button is set on and I stick the car in park
after driving around, the RPMs will oscillate between about 1000 and
2000. While in this state, if I turn the A/C button to off, the
oscillation stops; If I turn it back on again, the oscillation starts
again; and so on.

Any ideas?