Cold air when car is idle?

[SandEagle]

so the heat in my ride comes out hot when im driving. but when i come to a stoplight or if the car is running idle, it blows cold air. whats up with that? something need to get fixed?

 

[thescreensavers]

air in coolant?

 

[LTC8K6]

Low coolant?

Weak water pump?

Blend door / vacuum problem?

 

[Vette73]

Whats the year make and model?

Start with the basic stuff.
Coolant level? If that is low could be when driving you are forcing it to move but at idle the air is blocking the way.

Blend door could be controlled by vacuum and messed up. Idle has more vacuum than driving. But should not be enough to cause your problem, usually.

Leak/Bad Rad cap. Pressure could be dropping when you idle and build up when you drive.

 

[marcin]

SandEagle, are you sure you have air conditioner installed in your car? From your description it seems that you haven't. Without air conditioner, you will get hot air only when your car is running, couse it's heat from car's engine.

 

[DivideBYZero]

Coolant level. Top it up.

 

[Pulsar]

It may be the above issues, or it may be a partially or largely plugged heater core that is only getting enough hot water flow when the RPM's are up and the water pump is putting out pressure.