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· Premium Member
2003 Sonoma SLS ext. cab 4.3L / 4x4
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There are also vacuum lines under the dash that might be loose or compromised. Another possibility is that the (vacuum) actuator diaphragm (controls the damper/ mode 'door') may be faulty. I'd start under the hood first.
 

· Been there Done it
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16,799 Posts
I di have a faulty actuator on the left end of the heater ducting. Above the gas pedal. Removing the spring in it cured the problem. But I also agree with the other guys. It's more apt to be a vacuum leak under the hood. Those hoses between the master cylinder and the ABS pump like to rot and crack or come off. Very common issue. The small ones are 5/32" if you need to buy some new hose.
 

· B4U Task Force
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35,545 Posts
I di have a faulty actuator on the left end of the heater ducting. Above the gas pedal. Removing the spring in it cured the problem. But I also agree with the other guys. It's more apt to be a vacuum leak under the hood. Those hoses between the master cylinder and the ABS pump like to rot and crack or come off. Very common issue. The small ones are 5/32" if you need to buy some new hose.
...the larger are 7/32".
 
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