My lincoln navigator 98 is not blowing out any hot air, even when it's set to 90 degrees

well it is a blend, mode door (dampers) problem
it is a purely air distribution error.
you must check them all, to be sure they all work correctly
the service manual covers it.
https://eautorepair.net/Marketing/Default.asp

if you fix one problem reading this manual you just earned $80
so the manuals are free, ROI econ 101.

check your blend door actuator

Since your blower is working and it is a heat issue,thats where we'll start,First thing is have you checked the coolant level in the radiator when engine is cold,make sure it is filled to top,next verify you have coolant in reserve ,Start your van and get it up to normal operation temperature,If your heat gauge on the dash works correctly it should be 190 degrees,Now lift the hood and locate the two heater hoses going into the heater assembly at the fire wall,Both hoses should be hot to hold on to,if both are hot and no heat inside your problem will be the blend air door in heater assembly.
if neither hose is that hot you need to replace the thermostat in the engine to get it up to 195 degrees.
if one hose is hot and one is luke warm then the heater core is blocked and to blame. hope this helps you.

the computer that controls the deflector motor are not responding and opening the door for heat, I'm sure you have climate control,check the temp setting sensor to the computer input first

Hi - There may be 2 separate problems. On my 1991 Lincoln Town Car, there is a Thermal Blower Lockout sensor that disables the heater from blowing until the engine temperature reaches a specific temperature. This way if you have vent or floor settings and 90 degrees set and it is winter, you won't get blasted with cold air. When the vehicle warms up, the TBL circuit enables the climate control to blow the hot air. If you use the flr/def instead of the floor or vent control, the TBL should not prevent the heater from working even with a cold engine. On my car, the TBL went bad and always prevented hot air from blowing on the floor and vent settings, even when the engine was hot. Another thing to check is a thermal limitor resistor. It is designed to cut off the blower at very hot temperatures, except if the blower fan is in the hi setting.

As far as the A/C is concerned, can you verify if the clutch is engaging or not? A rapid cycling of the clutch is an indication of low freon. If you are absolutely sure that you are fully charged on freon, I think there are 2 possible causes: (1) Bad pressure switch on the accumulator is indicating low freon that is telling the compressor not to work; (2) a blocked orifice tube.

red or white vac line disconected or broken in engien bay

Your problem is a faulty heater control valve. The design used on these vehicles allows for hot water to flow constantly and compete with the evaporator as there is no blender door. You have to replace the valve and possibly the control head. Meanwhile, you can bypass the valve to have cold air

PROB NEEDS 2 JUST BE RECHARGED. BUT STAY AWAY FROM THE DEALER. IT IS ALWAYS 3 TIMES MORE THAN A PRIVATE SHOP

try changing the thermostat if thats not it check and see if you have water leaking in the passenger side floor board if so then you need a new heater core

this is caused by the main cabin temp blend door actuator motor, in order to replace it or even check it the dash must be pulled out.