I just replaced my heater core and blend door on my 1998 F150 4.2 liter. I put everything back together enough to drive to work for a couple of days. my heater was working fine for about a week then it just started blowing cold air. When I put my dash panels back on I had to discinnect everything again. When I was finished putting the panels back on my heater was working again for two car trips around town know its not working again. Everything works except for the heat coming out of the vents. The blower is blowing, I can change were the air is blowing, and how hard. It just blows cold air.

Also it feels like my clutch pedal is harder to press, Its almost like it's compressing something. I don't know if there is a conetion.

 

So heat works everywhere except the vents?

 

I reached in the main vent when the dash board was still off and felt the core and it was hot but the blend door wouldn't open. but cold air was coming out of the vent's.

 

Well if the blend door wont open that is your problem. It should be controlled my your variable temp. switch under the radio. Might be the switch or the door motor.

 

its possible your new heater core is plugged up with junk if you didnt flush your system and put new coolant in it. If not then it sounds like the blend door is gone. The blend door runs off vacuum, so does your clutch master cylinder.

 

Is it possible the my blend door is working and the temp of the water in the radiator is just warm? I felt the lower radiator after I got home last night (about a 45 minute drive) and it was only warm, but the upper hose was hot.
Could this be the thermostat? I just changed it but I did get the new one from KRAGEN and I've gotten crapy parts from them before. If the thermostat was stuck open then the 45 minute drive would not be long enough to heat the water up.
Could it be the water pump? If the water pump was bad then the water would just sit in the engine and not circulate through the heater core. I have heard of cases were the water pump was bad and did not efect the over heating factor.

 

The upper radiator hose should be like 250+ and lower radiator hose should be 190

Possible the water pump is bad, does it show any signs of leaking underneath it? or seapage from the weap hole?

Tstat is between the block and the upper radiator hose, so if youve got really hot temps at the top of the radiator hose, and near room temp at bottom, maybe the radiator is plugged up.

And yes its possible that after only 45 all the water hasnt heated up. You have to understand that the coolant system holds i believe 3 gallons of coolant. That is alot to heat up, especially when its moving around, and going through the heat exchange (radiator)
-Patrick

 

I have not noticed any leaks, however acouple of weeks ago I ran really hot, When I chcked my water I realized I was really low. So I very well could be leaking.

 

Could be a water pump or a radiator. Radiators tend to get a lot of crap in them (casting sand) after 100,000+ miles...

 

Patman03SprCrw is probably right, sounds to me like you have a vacuum leak somewhere under your dash or maybe even in the hood. I wood double check your connections at the blend door. If that doesn't work devote an afternoon and a couple of beers to chasing down a vacuum leak. They suck, so try not to get frustrated. That's the one thing i hate about Ford HVAC is vacuum motors instead of electric servos.

 

I have heat now!!! I flushed the radiator and my heater works fine now. I want to thank everyone that took the time to help me I really appriceate it alot.

 

I have heat now!!! I flushed the radiator and my heater works fine now. I want to thank everyone that took the time to help me I really appriceate it alot.