Heater problem when engine idle

Sounds like a vacuum problem with the heater controls.

Make, model and year of vehicle would probably be good information to include in a troubleshooting question like this.

He answered his own question, system is low on coolant, at idle no coolant flowing through heater core. Vacuum more of a problem off idle. Vacuum is usually at its highest at an idle. I've run my poor old 87 S-10 Blazer so hard a time or two that the 2.8 didn't produce enough vacuum to hold the vents open, ac blowing out the defrosters, the default position. But you are correct on one aspect,. year make and model should be in the first line of a post for help.

Whitelightning

when you fill it with water ,or antifreeze, the problem will go away. it is so low that the water does not circulate in the heater core until you rev the engine and more water is pumped through the heater. old john

Hello, Anon! You wrote on Tue, 25 Oct 2005 22:52:31 -0600:

A> Anyone have an idea what this could be? My friend's car has a problem. A> When he's idle and has his heater on, cold air blows out of the vents. A> Soon as he accelerates and moves, warm air blows out. Not sure what A> this could be.

A> He is running low on anti-freeze though and will fill it up. Don't A> think it's a thermostat issue.

With best regards, snipped-for-privacy@comcast.net. E-mail: snipped-for-privacy@comcast.net

Anan,anytime you have a problem with any unit that uses fluid on any vehicle check the fluid level as a first action.Post in usenet after if still a problem.