I have never been able to communicate with any of our BAC2k via rs485 only rs232.
From personal experience:
The BAC2000 uses rs232 via pins: 3 (TTL TX), 13 (TTL RX) and 15 (GND)
The BAC3000 uses rs485 via pins: 10 ( RS485 Data +), 11(RS485 Data -) and 15 (GND)
Make sure you try both of these...