In our 2015 38GK, the thermostat is directly across from the pocket door that separates the bathroom/bedroom from the kitchen/living area.
A lot of air comes in around both sides of the pocket door and in the summer it causes the A/C to run excessively.
Has anyone figured out a way to keep the air from coming in? Sometimes the thermostat says the temp 82 and we know the living room can't be more than 75, while the A/C just keeps running.

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If I recall your GK is the same stair design as my FB & the return air for the furnace is under that small pantry. I can see all the way down into the garage area from the gap under the pocket door so if blocking it off you'll have be careful not to totally block off the furnace return air.

Mine has 4 return air vents in the ceiling, nothing under the pantry. In cold weather, we feel cold air coming through, but we try our best to avoid cold weather.
I was thinking about getting a heavy, thick piece of plastic and hanging it there with velcro, just to see if it makes a difference.

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Mine has 4 return air vents in the ceiling, nothing under the pantry. In cold weather, we feel cold air coming through, but we try our best to avoid cold weather.
I was thinking about getting a heavy, thick piece of plastic and hanging it there with velcro, just to see if it makes a difference.

The ones in your ceiling are ONLY for the air conditioning & heat pumps, they have absolutely NOTHING to do with the furnace.
You WILL have a furnace return somewhere (not familiar with your floor plan) under a cabinet near the stairs & one up stairs in the bedroom somewhere under a cabinet that draws air from the garage, if you don't have these somewhere they screwed at the factory & your furnace won't be very efficient. Look in the ceiling in the garage, you'll find a register, mines in the door side compartment in the ceiling front corner which puts it under the dresser far right corner in the bedroom, that's pulling air thru to help circulate warm air into the basement/garage.
If you look closely at the photos you can see the furnace below that area.