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