92 GMC Sierra 1500 4WD Heater Vent Knocking Noise.


Old 12-08-07, 10:55 AM
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Join Date: Dec 2007
Location: Sierra Nevada Foothills
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92 GMC Sierra 1500 4WD Heater Vent Knocking Noise.

Last night when I shut off my engine, I heard a knock in the heater vent. It occurred about twice a second for 15-20 seconds. After it stopped, I restarted the engine, and it started again. I switched off the Heater blower and it Quit. When I turned on the Blower it started again. Puzzled, I went into the house to mull this over. Came out about 4 hours later, just turned on the ignition, and it started again.

I've been looking on the Internet for Data and haven't found a definitive answer yet. After I found this forum I saw a Question from someone about a year ago, but no Answer...

I've signed up here now and seen a lot of information passed on by some pretty sharp People, so I'm hoping for some tips...

Thanks a lot in Advance... PUMA...
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Old 12-08-07, 12:29 PM
Join Date: Feb 2005
Posts: 579
The noise you hear is one of the actuators that control the doors in the HVAC case. You may have to take apart some of the dash parts in your truck to determine which actuator is making the noise. Open the glove box and remove the compartment pocket, just a few screws, 7mm socket. Put your ear in the area you have the noise emitting from. Look around and see which panels of tha dash look to be removable, and remove if needed. Our plow truck does this also, but no need to put anymore money into that beater. It has been awhile since I tore into a dash on a truck like yours, so I cannot really tell you what parts of the dash can come off for access to the actuators, beside the glove box compartment.

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