N14 still issues with heat in cab after $$$

1. At idle there is less heat loss and heat gained from exhaust under the floor. Try opening all valves in the system to max heat and run for 30 minutes or so with the radiator cap off. this is to remove an air left in the system after all the changes. Bump idle up to 1K.

The next Q is how is the actual coolant temp at speed? Again more heat loss at speed. If temp is too low likely a thermostat stuck open.

Hope this helps. The fan speed thing sounds like bad wire or switch, does the variable work on vent?

 

Are all 4 valves open...He has a sleeper cab too?

What's the running temp going down the road?
Also...is there a manual fan switch?


I have to agree with Pawnd about the switch....

 

Hmmm...is that an OEM thermostat?

Some of those Chinese aftermarket parts fail right out the box.....

 

Now you got me thinking.......

On my KW there's a resistor (?) on the plenum.....
It looks like a loose copper coil....that would go south and the heater wouldn't work....

 

With the control set to vent, you are picking up outside air. This will do two things. One is that as he is driving down the road, outside air is forced through the vents as if the fan is on. Two, this very cold air has a hard time getting heated up as it flows through the heater core, causing cooler air.

With low engine temps and the air control on vent, the heat will never be warm on very cold days.

Change thermostats and run the inside air on recirculate to keep the cold air out.