Sounds like you may have multiple problems. The only common point of failure that could cause both the a/c to not run and the air to be directed out the incorrect vents is the pushbutton control unit. But you sure don't hear to many complaints of failure about this part on the 126, so I doubt it's your issue.
Most likely you have a problem with one or more of the vacuum pods which move the little doors which direct the airflow of the climate system. You'll need someone who really knows the climate system to evaluate it. Don't know how difficult replacement is on a 126 - it varies from chassis to chassis.
Are you sure the compressor is operating? Did the shop check the high side/low side pressures? We really can't give you any more diagnosis over the 'net without more information. There are a multitude of possibilities for the has freon/won't cool problem scenario.