1995 Pontiac Firebird no pwr at harness plug on ac/heater b

I got a problem with the control panel. Theres no power at harness plug on blower motor speed control switch. fuse good. Put 12v. To back of harness plug only works on high speed. No low or medium speed. Could the AC/heater control module be the problem? . And is it the little black box with wire connector.in front. and wires coming out of box going into heater core box.?? How do I check to see if module is good. Thanks. Gh454.