Dear liblonana -  It's colder in the winter than in the summer.  Actually, convertibles on the whole are sealed fairly tight nowadays, not like back when I was a boy and a convertible top was hardly anything more than a pup tent flapping in the breeze overhead.  Take a look at the car and look for damage.  Take it for a ride and listen for "excessive" wind noise.  Do you feel any drafts?  And most importantly does the heater work properly?  Good luck from Bovan.

i own a 1987 cabriolet and my heater works super.....i live in nebraska and been driving it in 5 degree weather....but i can put up with a little chill for 42 mpg!!!