what would cause ac/heater not towork? on 1995 Buick Park Avenue

my ac/heater works pretty much when it wants to, but a majority of the time it doesnt. i replaced the blower motor but i keep having the same problem. i even tried to replace the unit with the temp controls.

2 answers
You mean blower won't run? If so check blower,fan, resistor.
be more specific on your question