If there is no air coming out at all, then the switches, resistors, or the blower motor itself is probably not in good shape. Or the air could be blocked by some debris like leaves. If the air blows, but it's not warm, then you may have an air pocket in the coolant, or you may have a heater valve that is disconnected from the rotary knob, or something may be wrong with the heater core. (Hopefully not the latter, as it's a major pain in the butt to get at!)
"Mango Bango", 1990 CRX Si -- Sold on 10/01/11, with over 227,000 miles.
VTEC is Honda's "select a cam profile on the fly" system; VTECH is a crappy phone.