Q: The front heater works only at high RPMs and the back only blows cold air

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My vehicle has an issue with heating. Actually, there are two separate heaters that are controlled separately. One is in the front and the other at the back. The back one isn't toatally unresponsive, but it doesn't heat just blows cold air. Whereas, the front works when the RPM is about 2500. Please give me some suggestions. Thanks.

There are two distinct possibilities: there is either no warm coolant to the rear heater core or a blend air flap is permanently in the cool air position. With no warm coolant to the heater core there will be no way to get the air in the hot air circuit. If the blend door is not moving in the rear climate control box, then air is only fed through the cool air side and not the warm air side.

A temperature check of the rear heater core will determine if coolant is being circulated through the core, and an inspection of the blend air flap and control on the rear climate box will determine if air being drawn through the warm air circuit. You may want to enlist the help of a mechanic, such as one from YourMechanic, who can diagnose and correct the rear heater circuit.

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