If you are talking about dual heating (front/rear), then either the rear temp control is set to cold, or the control is not working.
A cold front
Cold
A cold front because a warm front would be hot and humid
A cold front usually causes the most violent weather
when a cold air front meets a warm air front
a cold front
A cold front brings in cold air. The cold air causes warm air to rise quickly. The rising air forms cumulus clouds. There is often heavy precipitation at a cold front.
Cold Front-When a fast moving cold air mass runs into a slowly moving warm air mass Warm Front-A fast moving warm air mass collides with a slow moving cold air mass Stationary Front-When a cold and a warm air mass meet, but neither one has enough force to move the other Occluded Front-When a warm air was is caught between two cold air masses
A cold front as this causes a lot of rain in a short period of time. A warm front causes light rain for days at a time.
when a cold air front meets a warm air front
A cold front stays on the ground, while the warm air mass rises to the sky and condenses into clouds.
The type of weather front that cause the most violence is a cold front. They can contribute to strong winds, major thunderstorms, and heavy rain.