Nissan Repair: 1997 Nissan Quest, heater hose line, heater control valve

Question
Let me begin by saying i am a novice at vehicle repair. I am somewhat mechanically inclined and can fix what i understand....... but.........

I am trying to figure out what can cause my heating problem. When i warm the van up, the heater will work fine as long as the RPM's are above 1500 or so. as soon as i stop at a light and the van drops to idle it starts to cool off and blow cold air. As soon as i resume the RPM's its fine. After about 20 minutes or so ( when it gets good and hot) it will stay hot... I replaced the thermostat and flushed and replaced the antifreeze. neither had any positive effects. Any ideas? thanks in advance

Answer
Hi Jon -

It seems that you have done a good job at checking all you need to.

One more thing you can check is your heater control valve. It is a vaccuum operated device connected to your heater hose. Open the hood, and follow the heater hose line until you see a valve with a vaccuum hose attached to it.

As vaccuum increases with engine RPM, my guess is it is stuck at idle, and when you accelerate, it frees up. Replace it, and you should be fine.

Hope this helps
calvin