Hi 'reyrey39'
I have cold urticaria too and it's been many years since I had it. My condition has gotten better over the years. Probably due to my body being able to adapt better to the cold. I don't live in a 4 seasons country so winter is not a problem for me but there are many other environments like air conditioning, rainy days, etc that can cause me to break out.
The passing out reaction your son gets is called anaphylaxis. It can be life threatening if the throat swells up and oxygen can't get into the body or the BP is too low and medical help is not near. I'm sure his doctor knows about his fainting and has prescribed an epi-pen?
When we get hives, fluid in the body leaks out and thus causing the blood pressure to go down and sometimes when it's dangerously low, it can provoke an anaphylaxis attack. The symptoms of an attack that's coming are, feeling faint, swellings, hives, throat closing, feeling of 'doom', ... The epipen should be given as soon as possible before the attack gets worse and then head straight for the ER. The epinepherine from the epipen doesn't last forever, medical treatment in a hospital is a must.
Swimming can be dangerous too. Even on a hot/warm weather, a cool breeze that touches the skin or after getting out of the pool can start an attack. Drying immediately is important and always have the epipen near. There are many cold stuffs to avoid and sometimes it can be hard to do so. Keep your son indoors during as much as possible. If there's a need to leave the house, make sure he's covered up warmly and nicely. Personally, I think 2 epipens are better than 1 in case the first pen is spoilt. Check the expiry date regularly and replace once expired.
As time goes by, you'll be more experience in dealing with his condition. And you will be more familiar with what causes him to break out and when some reactions are worse than others. There's information on the web and reading more will help you and your son alot. On a hopeful side, your son may one day grow out of this horrible problem... If you have any other questions, feel free to ask!

Good luck!
p.s. if you would like to read more, search Mastocytosis. It's another condition where too many mast cells are released, causing anaphylaxis.