Nut on top of cabin air filter (flanged with rubber washer)

[Jon Jon]

I was changing the cabin air filter in 2014 Chevy Silverado High Country 5.3 L today (behind glove box) and found a nut lodged in the top of the filter.  The nut was on the left top side of the filter.  The nut size would use a 10 mm socket and accepts an M8 sized bolt.  The nut is flanged with a rubber washer attached on the back also.  I looked into the air filter box (limited view) and also around the cowl under the windshield washers (did not remove the cowl...yet).  I am guessing it came from above the air filter- not sure if it just fell through the cowl black plastic cover on the wipers, or if it was part of a bracket in the HVAC system or other part. Does anyone know where this nut might have come from?

[DeePa]

Could be something from the blower motor housing. Usually those rubber backed flange nuts acts as a gasket. So I think that it was used to seal outside air from coming in to the hvac system from under the hood somewhere. 
 
have you looked up parts diagrams yet? How about a service manual?

[Jon Jon]

1 hour ago, DeePa said:

Could be something from the blower motor housing. Usually those rubber backed flange nuts acts as a gasket. So I think that it was used to seal outside air from coming in to the hvac system from under the hood somewhere. 
 
have you looked up parts diagrams yet? How about a service manual?

Hi Dee Paw - thanks for the reply.  I tried the parts diagram but did not get much luck.  On the HVAC diagram, it has a filter housing unit that sits above the filter (plastic) but does not show any nuts in the diagram. 

https://www.gmpartscenter.net/v-2014-chevrolet-silverado-1500--high-country--5-3l-v8-flex/hvac--blower-motor-and-fan

 

I could not find a detailed service manual - does anyone has a good link service manuals / diagrams - especially for HVAC and what sits above - that would be useful?