not blowing but generating heat
Did you check to make sure its properly charged? Is it R12 coolant or R137a? If the latter and your car has been converted, then you can check it yourself. If its R12, you'll need to take it in to be charged and checked (you might be able to find some R12 on ebay.)
If it charges and then doesn't cool, you might have a leak...thats a 'whole 'nother thread.
If you have R137a...it might not cool as much as you'd like. The older cars have a condenser thats not big enough, and R137a just isn't as good as R12