Because air comes from the vents, the blower is working. Check the small plastic vacuum line through the firewall for cracks, since the temperature control uses engine vacuum. Check both heater-core hoses; if they are not both hot, the heater core may be clogged. After the long sit, also flush the cooling system and replace a possibly sticking thermostat.
The owner of a 1988 Ford Tempo said the heater worked before the car sat for about four months, but now the vents blow only cold air even after the engine runs. An expert confirmed the blower is working and advised checking the vacuum line to the temperature control and whether both heater-core hoses get hot. Another expert recommended flushing neglected coolant and replacing a sticking thermostat.
