N14 still issues with heat in cab after $$$

Close off the fresh air intake for the heater at the cowl or under the hood if possible. It's been a little while since I drove a FLD, but I know the fiberglass housing is on the passenger firewall, but I can't remember if you can get to the opening easy or not. I do know the rubber nipple at the drain will rot off and let exhaust fumes in if you have any kind of exhaust leak.

 

With all the on and off, it is common to get air trapped in the system. It will stop water from moving in the heater cores or only let you get a small percentage of function. After changing coolant need to let get to full temp with the radiator cap off to purge the air from the system.
Also, when you heat water/fluids they hold less air so as system heats up you force the air in solution out of solution.

Close off bunk heaters and run up to temp with cap off, then close off cab and open bunk system with the cap off. When I was in the arctic this was one of the most common cause of poor heat in a vehicle.

 

I'm pretty sure your right about the door but freightliner only uses outside air for heating except when running defrost. Don't ask why either.

I think alot of the problem is the new radiator. The circulation is too good and the temps are too low. I'm gonna assume that in all motors they have a bypass around the thermostats, Cats do I know that. With the temps being extremely cold and some air is getting to the radiator its not allowing the motor to build enough heat. I had this issue with mine.

Couple things he can do, next time he stops, make sure he plugs that fresh air intake atleast 3/4 of the way and make sure the plug is in the bottom like sombody else said. Then very carfully grab the bottom radiator tube, if he can hold his hand on it tell him to check the side tank on the radiator. Tell him to be careful to not burn himself which I doubt he will do in these temps. Best thing to do is try it with his glove on first.

Someone said to try to get the cardboard in behind the Air-Air...You can't and even if you could don't! If it gets wet and you try to pull it out, it will rip and then you'll have to take off the Air-Air to get the pieces out. Anyway, over or under, there still won't be any air flow.

 

He didn't use Bars Leaks or something similar to try to stop a radiator leak did he? I have heard that stuff can plug the passages in the heater core.

 

Kevin Rutherford would tell him to slow down to 55,put a turbo 3000D and a OPS1 system on and see if that helps. Seriously,I had a 96 FLD and for 8yrs I tried tofigure this problem out doing everything already mentioned here,with no luck.Around 30deg it was ok but at 20deg it was aggravating.I finally gave up and just drove in a heavy flannel shirt.I know that it worked great once so that is what's aggravating,scratching all your hair out.lol

 

Did'nt Rick have the same trouble one yr on Ice Road Truckers?It froze a jug of water sitting in his floorboard.I told my wife I new exactly how he felt.

 

Good chance it is that valve! I had the same thing happen to me a cpl years ago. Sitting still you'd roast, but as soon as you started moving up to speed it would blow cold air out. I got lucky and knew it was that valve as the lever was stiff until that butterfly inside that valve broke loose from the shaft.

Sad part is.... It isn't like the older valves that you could take apart and open the butterfly all the way.