My AC, vent, and heat only come from the defrost, despite what postion the switch is set to. occasionally, it will come from where it is set to but only for a few seconds then it goes back to coming from the defroster. For example, I had the Max AC on on the way to St. Louis (about 1.5hrs away) and the ac came out of the defroster the whole way except for a few 5-6 second spurts where it came from the front panel. I have heard there is some sort of switch under the dash somewhere....is this true? if so what is this called and where is it located. If I was misinformed let me know what my problem may be.

Thanks for the help

 

What year/model? Mazda trucks after 93 are Fords and use a completely different system and pre-94. Sounds like a Ford which are vacuum operated so theres a vac leak which will need to be traced.

 

Yep, 1993 and earlier Mazda trucks are made in Japan and the diveror doors /flaps are cable controlled, one needs to look underneath the dash and up as a helper moves the levers and one can determine which cable and on which side of hump has become unattached. (That happened once on my '88 Mazda)

Since 1994 Mazda truck is same as Ford Ranger, and those flaps/doors are operated by engine vacuum, and yours sounds like the default mode. Maybe one of the vacuum "motors" is bad, or a vacuum hose has a crack or has slipped off. (The vacuum "motors" went out several times on my '88 Cherokee)

 

it is a 2000 B4000. are these vacuum hoses under the dash?

 

They start under the hood and run into the firewall so start tracing under the hood.