1996 HVAC Blows Hot Air Only

1996 Sedan Deville blows hot air only. Checked R134a charge both low and high side which is well within specs based on the temperature and humidity. So the A/C part is fine. Problem appears to be a bad climate control unit/programmer or possibly a vent actuator in the dash. Engine vacuum from the intake manifold into the dash is good.

Does anyone have the procedure to run diagnostics at the climate control unit?