[77newell]

My 93 39ft coach will turn over but not start without preheat when the temperature is below freezing. If yours is not turning over then neither the cold nor possible gelled fuel is the immediate problem. If indeed the starting batteries are good AND fully charged, then you have some kind of electrical problem, likely a bad or corroded connection somewhere. Get your handy voltmeter out and measure voltage starting from the batteries and going to the starter itself. If those are all reading 12+ volts when the key is switched to the "start" position, then you have a ground problem. One way to find a ground problem is to engage the system and measure voltage between battery "-" and the grounding wiring starting at the engine. You will have 12 volts showing up in the ground system until you reach the point where the bad connection is. Until you get the starter rolling the engine over everything else is irrelevant.

You could also disconnect the house batteries as described above. Engage the "merge" solenoid and check to make sure it is engaged. I believe it's possible to start the generator in this configuration. If it cranks without hesitation then you will still need to figure out why the drive engine starter doesn't engage. If it doesn't then you know there is an electrical problem somewhere close to the batteries, or so I believe.

Your drive engine preheater is powered as Forest said by the top receptical on the 120v box mounted on the forward side of passenger side engine compartment. You must be connected to 120v or have the generator running AND have the preheat switch above the driver's head (if the same as my coach). It will take several hours of preheat before the engine is warmed enough to start. With the preheat operating I have been able to start the engine down to 3 degrees (why the heck anyone wants to travel when it's that cold is a mystery but I've done it).

If the fuel in the tanks was purchased in the summer it is possible that it will gel. You can buy additives by several vendors that will dissolve the gel. I would add that to the tanks prior to cranking. I've never had a gel problem even with "summer' fuel being used in the winter but that doesn't mean it doesn't happen.

If the fuel has been sitting for some time I would install new fuel filters filled with good clean fuel. I would have a few extras in case algae has grown in the tank. My coach as set outside for months and I've never had algae but you want to be prepared.

As for airbrake antifreeze. On my 77 coach there was no air drier after the compressor on the engine. Passing through an ice storm (really dumb move) into really cold weather I did have problems with my air brakes. Once I installed an air drier I never had further problems in freezing conditions. A well maintained modern drier will remove enough moisture to keep you safe. If I ever do develop a problem my plan is to dump the air in the system and pour some air brake antifreeze down the exit line from the drier pressurize the system and then pump the brakes to move it through the system. I don't know if that will work but it's worth a try if you find you have problems, but I would do nothing until you know you have a problem with icing. The more you mess with things that aren't broke the more likely things are to break.