This is a dual climate control system, which is the same system that g.M used in the cadillacs of that year. The system is very involved and difficult to diagnose.I would suggest that you take it to a competent shop for diagnosis. It requires specific tests and tools and procedures.I can tell you this there is a very high failure rate of the main controller which g.M calls the control head. And it is very expensive. Do yourself a favor and have a pro diagnose it for you.