I have a 2000 lincoln navigator that is having heating issues. I have 135-140 degree heat coming in and out of the heater core, but cool or luke warm air coming out of vents/defroster. I cut a small square in the heater core box and noticed that the blend door is working, completely opening and closing to the heater core. In the attached pic, the heater core on the left is hot, and the evaporator on the right is ice cold, so I am getting a mixture of those two temps. I saw the blend door that opens and closes to the heater core, is there one for the evaporator also that I can't see????? Thanks

PS. The rear heat works fine, just the front is getting the blended air.

 

Do you have the EATC (Electronic Automatic Temperature Control) or the manual system? Being a Navigator I'm guessing it is the EATC.


The Blend door (there is only one), "blends" the heater core air and the evaporator air to achieve the desired temp. The Mode door directs the air flow to the desired outlets.


When the Defroster mode is selected, the EATC sets the Blend door to direct all incoming air through the evaporator core and then through the heater core, and the Mode door then directs the air to the defroster outlets. (The theory being that the evaporator will dehumidify the air and result in quicker demisting of the windshield.


When you raise the temp to 90* does the EATC move the blend door to direct all air through the heater core?


And are both heater core hoses hot to the touch?

 

Yes both heater hoses are hot, I was using a infered thermometer and it was reading 135-140 degrees on both hoses. It does the electronic control. When you turn heat to 90, the blend door opens, when you turn it to 60, it closes. Because of the hole I cut, the air is coming out hole, so I am unsure what you mean by how the air is being directed. Thanks

 

Should be a good 60-70° hotter. Did you measure on a metal (most accurate) or rubber (will read cool) section of coolant line?

What is the temp at the thermostat housing?

 

I replaced the thermostat tonight and did not see any changes. The top heater core hose is about 160 degrees on the metal clamp, other core house about 135. I have 175 degrees at the thermostat housing after running for a 1/2 hour. I noticed the top radiator hose is soft and does not feel like there is coolant in it, and when I unscrew the overflow tank cap, there is not pressure being released.

 

Choose your poison: low coolant, low flow, or clogged/restricted heater core.