Nissan Repair: Heater, vacuum line, defective valve

Question
My heater blows cold air.  Could you please give me some possible causes.

Answer
Hi Lorrie -

Did not get the year, make and model of your car, so I will answer what I can.

The heater system is controlled by an in line valve on the heater hose, usually near the firewall inside the engine compartment. Look for a device that is connected to the small heater hose, usually connected to a vacuum line. If the heater has not heat, the cause normally is a defective valve, or loss of vacuum to the valve due to a broken hose, or defective source.

Hope this helps -
aloha
calvin