air cond/heater fan speed switch

I have a problem with my fan switch in my 1997 b2600. When i slide it across to speed 1 or 2, the fan doesn't work but the air conditioner kicks in. Then if i slide it to 3 or 4 the fan works but the air conditioner stops. Can anyone point me in the right direction as I've taken her to couple of mechanics who didn't have a clue. Thanks in advance as its coming into summer in Oz and where i live gets pretty hot.

"I've taken her to couple of mechanics who didn't have a clue."

OK, in Australia 1997 B2600i is like USA 1993 B2600i. So I can help, in fact - I know EXACTLY what the issue is. You have a bad blower resistor; your symptoms are classic. Sad that "a couple of mechanics" were clueless.

There's a real good write-up here - in fact I wrote it - see http://www.mazdatrucking.com/forum/showthread.php/12985-Blower-motor-and-blower-resistor-check-out

Thanks Cusser you are totally awesome and have made my day.Thankyou very much for solving my problem. A very happy Aussie, regards Hay esy