Heater and air conditioner problems. on 1990 Buick Skylark

When I turn on the heater and the air conditioner, I hear like an air escape but it is not working, What can be the problem?

Asked by for the 1990 Buick Skylark
you might need a new compressor, I needed a new one on mine about 3 months ago (2001 Infiniti Qx4, 78,000 miles)