Cars & Vehicles
Heater Cores and Blower Fans
Jeep Grand Cherokee Limited
Car Heaters

Heater and ac only blows on defrost?

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Answer

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Wiki User
02/13/2014

Many cars use engine vacuum to operate HVAC controls. If vacuum is cut off the system defaults to the defrost mode. Check the HVAC vacuum supply hose under the hood leading from the engine. It may be disconnected or damaged.