My 92 silverado has periodically blown warm air, but now just blows cold air which doesn't help in a Wisconsin winter. Need to know what could be causing this.

 

Could be alota things. Id start checking the heater core hoses. Both hoses should be nice and hot. If one hose is hot and the other cold u got a pluged up heater core. U can backflush the core by taking both hoses off and tunning water through each side. also make sure your antifreeze is up to lvl.

 

Fill the radiator and check for coolant leaks

 

Is the coolant full? Does the temp gauge go down while you are moving? Could be a stuck open t-stat