1993 Ford Tempo heater and defrost buttons not working

your question is too vague to pinpoint problem.but it sounds like you have no vacuum to heater control unit.all the venting positions work off vacuum.also the heat slider lever can become non functional which means even if you get the air to change venting it has no heat.the vacuum line goes thru the firewall behind engine and it is a small hard black plastic line.it should be right above upper air conditioning pipe coming out of wall looking down behind engine from passenger side of car.once you verify that is ok(not damaged,connected to vacuum source) then check connection on back of heater control itself.it's a soft clear plastic plug with some diff color lines going into it.they are color coded to ensure proper placing of connection.if you still have no heat then it's likely the sliding heat lever has become loose/broke.tempo heater controls are a veritable pain in the butt.