Locomotives have to have forced air heaters to act as defrosters. Hot air is blown onto the inside surface of the windshields through ducts in the window frame.
Some of the newer models have defroster heating strips in the glass like auto rear windows.
Electric heaters seem to work better than hot water heaters. They get hot faster, and do not need to be drained if the loco is left shut down in cold weather.
Sidewall heaters work well to defrost the side windows.
Some locos are equipped with electric strip heaters below the side windows at floor level. They can also be installed in the front wall of the cab.
The hot water heaters in the old Geeps and SD's were not very good, especially as built. There were two heater fans on the back cab wall, one on each side. They were powered by open-frame motors that gave a lot of trouble.
Like heater cores in old cars, the heater cores in old locos were prone to leaking. Once, after pulling a long grade up a mountain in a GP30, the rear cab wall heater on the fireman's side ruptured. The cab filled with steam, and my conductor (who was sitting directly in front of it) got a full blast of it. I had to shut off the water flow to the heater and air out the cab before we could continue.
As to the brake question, the 26L (don't ask me what the numbers and letter means, I don't know) is a late, perhaps the last, manually-operated freight brake valve. It does not have the "lap" position to maintain pressure like the 24-series that preceded it. You can make a direct reduction to any point in the service portion of the handle's travel, actuate the independent, and have a reasonable chance of maintaining that set. Second-generation EMD power came fitted with these, and most first-generation EMD power was retrofitted with it. The early Geep 7's (and probably early F's) were equipped with the 6HBL brake used on steam locos. These things did not have a pressure-maintaining feature, and were a real pain in the butt on a long downgrade if you did not have dynamics.
I used the term "manually-operated" because the newer units with the desktop controls, or the even newer faux side-mounted controls are not operated directly by manual force, but are "fly-by-wire". These new control consoles (like on an ES-44) use what look like 26L brakes, but in fact are computer-controlled with familiar-looking controls. I like the desktop controls best, unless you have to run a unit in reverse. I noticed on the newer CSX units there is an auxiliary speedometer on the back wall, very useful with the side console.
At night, running long hood forward, you can read the speedometer backwards in its refection in the back door glass. In the daytime, not so much.