So first off I live in the freezing cold Wisconsin and i was wondering if the cold will hurt anything on the air system? Also I need a new compressor and this is a budget set-up and i was looking at the Viair 280C or the Viair 325C for my train horns. Which one would you recomend?
add a little anti-freeze in your tank so when you blow your horns it travels through your air lines & valves to keep them from freezing.
I recommend the one that delivers the most CFM.
My check valve kept freezing so I just had to unhook it for the winter 
As Dan said you should go for the most CFM for your budget. As for the cold you, how much do you intend on using the compressor in the cold? What size tank are you thinking of? How cold is “cold”? And on what kind of vehicle / where on said vehicle are you thinking of mounting all this?
I live in Canada and run dual Viair 480c compressors on a 5 gal. tank. My compressors tend to work harder in the cold drawing much more amperage and they also compress air slower so it takes longer to fill your tank.
All the trouble the cold has given me so far is my valve likes to freeze shut or open if I don’t use it for a while which is usually cured by a good smack with something metal.
i also live in canada (southern Alberta) and i plan on running a water filter before my tank. would that have a tendency of freezing up like an ice cube and becoming 100% plugged? or is the filter even necessary?
Water fiters (traps) work best on the output of a tank because the air is cooler coming out of a tank than it is going in. When the air is hot from the compressor, the water is suspeneded as a fine vapor which can pass through the trap but when the air cools down the water vapor condenses into droplets so the trap can catch it. Most of the water will be captured inside the tank.
I’ve been having some problems with my compressor lately with the cold. The compressor turned on the other day and it sounded like the RPMs went noticeably higher so I went under the truck to look at it. Air was being pushed out the air intake filter so I just un-hooked the power to it.
Later on when it warmed up I hooked it back up and it worked fine and no problem. This has happened a few times so I just un-hook it with the cold weather. My guess is seeing my air comp. and the tank are at the same level, the supply line to the tank is getting ice in there and not allowing the air to go through it? Either way it sucks and I cant wait for it to get warm again. 
05 Dakota. Northern NJ.
Temperatures are currently around 15-35 degrees F.
At night I leave my truck in my garage, but I don’t think it’s too much warmer than outside.
Should I be concerned as well?
Just make sure you drain it regularly and you should be fine.
By the way…I have a 400C compressor. I was reading on HB website that the 420, 460C, and 480C compressors are made to be outside.
Am I still okay?
Where is your compressor mounted?
I’ll be mounting it along my frame rail. It’s the only place I could find that would be able to fit a tank and compressor. It can’t go in the cab and there’s no room at all in my bed. I have a 05 QC Dakota.
Here’s what I used to have.
(PREVIOUS SETUP)
OK to be mounted outside - as long as you route the remote mountable intake filter to a place that can never become wet. Never, ever draw water into an electric motor. They’re better at pumping air than water! 