no hissing noises from my defrost switches when i turn them. nothing moves from defrost to panel to floor or anything where do i start troubleshooting?

are you having problems with your heat too, you may need a blend door. can you hear anything when you move the switch from defrost to heat or blend? if u have a vac leak use a can of carb cleaner to detect them. also located under the hood passenger side fire wall there is a heater connection u should ck. also ck your coolant level, t-stat, heater hoses,bybass hose from water pump and heater core. also ck fuses etc...

are u chasing a heat problem or a vac problem?