Automatic foundation vents not closing when it is cold

Is there a way to adjust these coils? Or are they replaceable? My HVAC guys says that are all sub-standard and that I should replace with manual ones. I am having a problem finding a manual one that looks as nice as these do. So now I wonder if I can adjust the coil. Worst case, I can put plastic over them during the winder months. Thing is, we are in NC and it cold then some days is 60 again. That is why I think the automatic vents would be nice (if they worked).
Thank you, Todd
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