Sounds like you have a vacuum hose disconnected from the A/C control panel, the vacuum connector that sits on the evaporator housing (can be seen from under the passenger compartment), or one of the vacuum canisters on the evaporator housing is leaking/disconnected. Also check the small vacuum hose that comes through the firewall between the a/c hoses going into the evaporator. Make sure it's not disconnected/cracked. I have a 99 so I'm not sure if yours is the same. Do you hear vacuum behind the dash when you turn the control to vent or a/c? | 
Help! Heater and A/C controls 
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