2002 Expedtion Eddie Bauer. Problem is lack of heat from both front and rear units. Don't think there is a blend door issue can hear the air change as the temp setting is moved up and down. Scan gauge said coolant was 180 degrees running down the road. Little low so changed t-stat temp now constant 189 at idle. Thermal / laser temp gauge gauge says neck on intake where the heater hose comes off is 173 degrees. Tee where lines split to go to front and rear heater cores read 140 degrees return line at tee reads 135 degrees. Diagnostic on the hvac head unit shows no errors. If you move off automatic to floor mode it makes a little heat laser gauge says 96 degrees. The only thing I can think of now is that maybe the water pump impeller is bad. Not moving enough coolant fast enough. Any body got any ideas on what is going on. Little lady isn't going like driving the Expy in cold weather.

 

I read in the past that there are restricters built into the heater core lines that get blocked from rust and/or trash. You can remove them, but the idea for them is to prevent blown heater cores.

I would look into this if you believe the blend door is working correctly. You will need to remove the "T" for the heater core lines and blow them out or flush to remove the blockage. Even then, if it has somehow lodged itself, then you may have to get creative.

 

Time to back flush both heater cores.

 

Well we put a new intake on this expy and flushed both heater cores and replaced the WP. Saw no issues with WP. At first it didn't act like we had fixed the heater. Then it started working and working well guess we moved an air bubble. Heater hoses and upper radiator hose now get hot enough you don't want to hang on to them. Intake was replaced for a p0174 code.

 

We are having the same issue on our 2002 Expedition EB. Front and rear heat are not warm. Thermometer says about 100 degree air is coming out of the vents. I replaced the t-stat, water pump and back flushed the system 4 times. Still same result. Heater lines are hot and blend door is working.

Finally broke down and took it to the Ford dealer. They put another new t-stat in it and that still did not work. They are now in the process of replacing the heater core. They said when they get blocked, it wont let the coolant go through the little passages inside the heater core and it won't allow the coolant to get back to the rear heater core.

 

The 2 heater cores are plumbed in parallel, so even if one is blocked the other would still work. The chances of both getting blocked at the same time is unlikely, unless some foreign material got into the cooling system. The back-flush should've cleared out anything blocking the cores, except for something hard like water mineral deposits.

 

What we saw come out of the rear lines was a syrup like substance. Didn't notice the front core was busy making sure flush lines weren't going to leak on an open engine. If you get good flow while flushing i don't see how it can be plugged. There is no bypass in them. We reversed flushed first then flushed in the normal flow direction.

 

In the process of fixing my luke warm air issue and I am going after the blend door first to make sure that isn't the issue first. When I first noticed that I wasn't getting much heat the shop it was already at said they would flush the system for $60 however it's still barely warm so i'm attacking the blend door and cutting my way into it to see if that is the problem before moving onto the next possibility of a clogged heater core.

 

Instead of hacking around on the HVAC plenum, do a simple check of the temperature of the heater core lines to see if both lines are hot, cold, or one of each. Once you have THAT information, you can easily determine where to focus troubleshooting efforts

 

On ours I drilled a 3/4 inch hole in the heater box and used an inspection camera to check the blend door operation. The hole was then covered with foil duct tape. I put it in an area where you would have to cut out if you replace the blend door with out removing the dash.

 

Good forethought.