Blows out cold air with thermostats pushed all the way to hot.

you might have a worn thermostat in the motor or you might need to drain the antifreeze and add new antifreeze

just to add, does the temp guage work and show normal temperature? if it does, then you may either have air in the system or the heater core may be clogged. Roy

mine did this before head gasket blew....gasket leaks coolant into engine and then you have no coolant and heat doesnt work