Heater Problem '98 XLT 4.0 L SOHC

[archer973]

Not surprisingly I've discovered a new problem with this vehicle. Just did a partial rebuild of the engine (see 1998 Explorer XLT Resurrection if you are interested). I'm sure I will be working out bugs on this for weeks to come.

Problem: Heater constantly blows hot air and heater control valve does not close. (I had my wife rotate the heater temp control while I lay under front of vehicle watching the valve). I tested the valve with a vacuum pump and it does operate, so I think it isn't the problem. Possibly I did not reconnect all the vacuum lines correctly.

Current routing of vacuum lines. There is a short (approx 9") L-shaped black vacuum line connected to the heater control valve. It is connected to a gray vacuum line that goes to the fire wall on passenger side underneath A/C stuff (that's a technical term). A black line comes out of firewall and goes to the vacuum reservoir. Another black line comes off vacuum reservoir and goes to top of engine where it connects to a red line that comes from the back of the intake manifold.

Questions:
1) Is this routing correct? If no...Help!
2) If I have correct routing, then how do I get into the heater controls to work on them?
3) Also if this routing is correct, why the short black line since the gray one is more than long enough to reach the heater control valve?

 

[archer973]

Found the answer to question number 2 above. Took the panel apart and got to the controls. Tested heat control rheostat with DMM. It tested good. Don't have a wiring diagram for this so not sure where to look next. Still hoping someone can advise me.

 

[crunchie_frog]

the vacuum wiring sounds correct. so if you are not getting vacuum to the heater control valve, have you checked the electrical/vacuum switch that ports vacuum to the heater control valve. If all of your other duct vacuum motors are working, then you have vacuum back to the correct place. You either have a bad switch or a leak on the vacuum line to the heater control valve. Of course, if the heater control valve is working and you get all heat, you have a bad blend dooor or blend door actuator.

 

[archer973]

the vacuum wiring sounds correct. so if you are not getting vacuum to the heater control valve, have you checked the electrical/vacuum switch that ports vacuum to the heater control valve.

Hi crunchie_frog. Thank you for responding. I'm not sure which switch you are referring to. I think your are referring to the one that has five or six vacuum lines to it. I haven't figured out a way to test it. It must be functioning at least partially because I can see one of the doors open and close.

If all of your other duct vacuum motors are working, then you have vacuum back to the correct place. You either have a bad switch or a leak on the vacuum line to the heater control valve.

The heater control valve does operate with vacuum from my hand vacuum pump. The only door I have observed is directly behind the glove box. I believe it is the recirc door since it is open for non-recirc in all settings except Off and Max A/C. So that vacuum motor works. I haven't disassembled anything to be able to see any other doors. I guess I could check for proper changes in airflow with different settings. I will get back to you on that later.

Of course, if the heater control valve is working and you get all heat, you have a bad blend door or blend door actuator.

The heater control valve does not operate so a leak in the line is possible. Where is the blend door? What do I need to disassemble to see it?

Thanks again for posting!

 

[crunchie_frog]

The switch with all the vacuum lines has one that goes to the heater control valve. Since you apparently are not getting vacuum to the heater control valve, I would disconnect the vacuum line at the control valve and try to pull vacuum on that line and see if it is leaking. If so you have to find the leak. If it is the switch, then it would not be porting so vacuum is getting to the line to the heater control valve and you would need to replace the switch. The blend door cannot be seen, it is a flapper that controls how much air goes through the heater core or through the ac evaporator. You might want to search for a vent duct diagram for an explorer on google and see what you get to give you an idea of how it all works. It sounds like you are getting vacuum back into the controls if the recirc door is working. Loss of vacuum defaults the air flow to defrost and the heater control valve open. The blend door is a pain to repair and the actuator can be accessed behind the glove compartment but also a pain to remove. There are lots of the threads on here about both the blend door and actuator.

 

[koda2000]

If you can't get the heater control valve to operate with you had pump, that's your problem. Replace it. As far as the blend door... there is an actuator which is controlled by a potentiometer on the TEMP control switch. This actuator (which is a PITA to remove/reinstall) is located behind the glove box. These actuators can and do fail and must be replaced. I just changed one on me '01 ST to fix my lack of heat.

Access to the blend door requires taking half the truck apart. If the blend door is broken most opt to cut a hole in the heater plenum to replace it (sealing the hole afterwards). There's a sticky on this subject.

 

[archer973]

If you can't get the heater control valve to operate with you had pump, that's your problem...

Access to the blend door requires taking half the truck apart. If the blend door is broken most opt to cut a hole in the heater plenum to replace it...

Hi koda2000. Thanks for your input. The heater control valve does operate with a hand pump, but when connected to the vacuum system, it never closes giving continuous hot water flow to the heater core. I will want to fix that problem someday but the bigger issue now is the blend door...it is broken.

I have cut a hole into the plenum as you suggested. Can't get the blend door out yet. The top pivot point of the door is not broken off, just a large chip in the top of the post that allows the actuator to disengage. Tested the actuator and it does turn. I need to find a way to break the door out now. I'm thinking a quarter stick of dynamite will break it out of there.

 

[archer973]

The switch with all the vacuum lines has one that goes to the heater control valve. Since you apparently are not getting vacuum to the heater control valve, I would disconnect the vacuum line at the control valve and try to pull vacuum on that line and see if it is leaking. If so you have to find the leak. If it is the switch, then it would not be porting so vacuum is getting to the line to the heater control valve and you would need to replace the switch. The blend door cannot be seen, it is a flapper that controls how much air goes through the heater core or through the ac evaporator. You might want to search for a vent duct diagram for an explorer on google and see what you get to give you an idea of how it all works. It sounds like you are getting vacuum back into the controls if the recirc door is working. Loss of vacuum defaults the air flow to defrost and the heater control valve open. The blend door is a pain to repair and the actuator can be accessed behind the glove compartment but also a pain to remove. There are lots of the threads on here about both the blend door and actuator.

Hi crunchie_frog. You've come to my rescue again. Thank you! I stopped looking for the problem with the vacuum to the heater control valve and will come back to it later. After reading your post and koda2000's post, I realized that the real problem must be with the blend door so I pulled the actuator and felt the top of the blend door post. It has a chip in the top of the post so that the actuator disengages. I cut a hole in the plenum behind the glove box to access the door, but have not managed to break it out of there yet.

I visited several threads and Youtube videos on fixing this. Some people cut an access hole behind the glove box as I did and some cut out the bottom below the door. Either way, breaking this door out will not be easy.

Just thought I would post an update. Thanks again for your input.

 

[archer973]

I got that puppy out

It wasn't easy, but I finally got the blend door out through hole I cut behind the glove box. I imagine that if the top of the blend door post had actually broken off, it would be easier to get the door out. But mine just had a chip in the top of the post so the door was still firmly in the pivot holes. My solution...

With the door closed, I pried up on it to get as much of the top of the post exposed as possible then used a hacksaw blade to cut off the top of the post. This made it short enough so I could use a pry bar to push up the top of the box enough to clear the post and get it out of the hole. After releasing my pry bar, the door was jammed in a upright position close to the door opening. I then used my pry bar to poke at the door to knock it down. But this also broke the door into two pieces that were easy to remove. I've just ordered a replacement door through Amazon Prime, Dorman 902-221 Blend Door Repair Kit.

Will post more when I install the new door.

 

[archer973]

Update

Well, the new blend door is installed and I can now control whether I get cool air out of the vents or hot air. There were some challenges getting it installed.

The blend door kit (Dorman 902-221 Blend Door Repair Kit) instructions directed me to cut a hole in the bottom of the plenum under the door. I had already cut behind the glove box, and had problems getting the old door out. I could not install the new door, so I cut another opening. Even then it was a struggle to get the door installed. The instructions state to insert the bottom post into its pivot hole first then the top. That is the way it finally went in, but it wasn't easy. I pushed, poked, pried, patted and other things that don't start with "p" trying to wedge that door in. Finally it just slipped into place with little effort. It was a matter of getting it at the right angle and I tried a lot of them. But I'm not sure I would have got it in if I didn't have the upper opening behind the glove box so I could reach through to help guide the door.

The kit came with enough peel and stick foil tape to seal both of the openings I had cut so that was a nice bonus for me. The kit instructions are on the Dorman website at this link: 902-221 Ford Explorer/Ranger Blend Door Installation Instructions

I still have not been able to get the heater control valve to close, but since we are having cool weather now that isn't a priority for me. I have other projects that need my attention first so I won't have any posts on this thread for awhile unless someone posts some questions for me. When I get back to the valve issue, I will post updates.