Vent controls, front always blowing

[Batx00]

Hi everyone, I bought a 2001 explorer xlt 5.0 a few weeks ago and noticed the front vents won't stop blowing air unless you turn the vent selector switch to off. This is manually controlled system, not the electric unit. When you put the switch in any position, it does redirect the air flow according but the front vents are always blowing air to some degree. The only way to shut the front vents off is to either turn the switch to off (thus turning off the whole system) or close the air flow flapper at each vent. Temperature control hot to cold works. The variable blower fan speed works. I looked behind the glove box and the actuator is opening/closing the door all the way depending on the mode. I checked behind the radio and everything is plugged in and looks fine. Could there be something inside the heater box stopping it from shutting the front vents all the way off? Do I need a new switch assembly? Is there a way to test the electrical part of the switch? Any ideas?

 

[koda2000]

If the directional knob is set on anything but OFF, the fan will blow. There is no OFF setting for the fan. The lowest fan setting is "1". The only way to stop the fan is to set the right hand selector knob to the straight up position, which is OFF.

BTW, Your next question will probably be about the A/C being ON when you haven't selected A/C or A/C MAX. The A/C can come on by itself in any setting other than OFF, VENT and FLOOR.

 

[Spuddy]

You have already tested most of the electrical parts of the switches, which are the fan speed controller and the temperature knob. If your AC clutch activates when you select A/C, then that electric switch is good also.

Sadly, the function selector switch is vacuum driven, as well as all of the control doors. When there is a vacuum leak, the system will default to the defroster registers only.

So, it is strange that your panel registers are always on.

There is a a floor/panel door and vacuum motor and a panel/defrost door and motor. Both doors would have to not be fully closing for some reason in order for air to still be coming out the panel registers. Seems unlikely.

So, perhaps your selector switch is clogged or damaged?

 

[Batx00]

Ya, it is weird. I'm wondering if it might be something wrong with the selector switch. I might grab another set of switches next time I'm in the junk yard. I'm pretty sure the AC clutch engages on the AC and defrost settings, I'll double check it. I haven't tried taking out/opening up a heater box in the junk yard yet and nor have I found any diagrams of the internal workings yet. Maybe I'm not searching for the right words. Do you know how the air flows through heater box? Does the air encounter one door before the other or is it going to both doors at the same time? I assume it has foam seals on the doors (I saw some foam on the door right side of the glove box), do those foam strips get old and wear out?

Koda, yes, it does that, which is a good thing and I expected it to do that. It operates the same way as my 06 mustang and my parents late 90s ranger pickup. The weird part is the front panel vents don't shut all the way off but the air volume they blow does change when in the different positions.

 

[koda2000]

Maybe you're not being clear. Are you saying that if you set the selector switch to FLOOR air is still coming out of the dash vents?

There are multiple doors inside the HVAC plenum. The one behind the glove box opens/closes the access to the heater core (AKA blend door). IIRC there are 4 other doors. Most are vacuum operated and control where the blower air is directed. If you always get air out of the dash vents when the fan is blowing, then the vacuum motor that opens/closes the dash vent door is apparently stuck in the OPEN position. You don't have a vacuum leak, or you'd only be getting air out the DEFROSTER vents.

Someone (drdoom? or turdle?) once posted a diagram showing the location of each door and it's function.

 

[Batx00]

Yes, it doesn't matter what position it is in, the air is always coming out the dash vents (with the exception of "Off"). It almost acts like something is stopping a door from closing completely. I'll see if I can find that thread.

 

[SCopeland]

Yes, it doesn't matter what position it is in, the air is always coming out the dash vents (with the exception of "Off"). It almost acts like something is stopping a door from closing completely. I'll see if I can find that thread.

I believe you and I are having the same problem, in different places. In my 2001 Explorer that I just bought, the air only comes out of the floor vents. I've looked everywhere I can in the cab with the exception of taking the console off and looking around behind it (will need a guide for that, I'd probably screw it up on my own). I've only just started troubleshooting today, have you come up with anything on yours?

 

[Batx00]

Not yet. I didn't have a chance to look into it today. I did find this thread, post 18 is the one that caught my interest.

://www.explorerforum.com/forums/index.php?threads/black-globe-vacuum-reservoir-on-v-6.169945/#post-1541279

The black globe and tubing is a good place to start. I have quite a few theories right now but I need my vacuum gage, which is at my dad's shop... That will at least tell me if I have low vacuum somewhere within the system.

 

[Spuddy]

I think I can post a diagram for that.

In a nutshell, after the air flows through the blend door, it next encounters the floor/panel door, and then the panel/defrost door.

The strange thing here is that a vacuum leak will cause the floor/panel door to default to panel and the panel/defrost door to then default to defrost.

I've got a small vacuum leak still and if I gun it with the a/c on, my airflow will redirect thru the defrost.

PS... I just looked at the diagram in the link above, which is a different version than I have, but functionally the same. Note that the 'nv' [no vacuum] positions for the doors causes the airflow to flow thru the defrost ducts.

 

[SCopeland]

Funny thing, my explorer has code P0174, doesn't look like it's the MAF causing it, and when testing that this afternoon we think we found a vacuum leak pertaining to it, just have to find where it's at. I may pop into the shop tomorrow and have them smoke test it so I'm not digging around. Vacuums, vacuums everywhere, so much fun.

 

[koda2000]

Funny thing, my explorer has code P0174, doesn't look like it's the MAF causing it, and when testing that this afternoon we think we found a vacuum leak pertaining to it, just have to find where it's at. I may pop into the shop tomorrow and have them smoke test it so I'm not digging around. Vacuums, vacuums everywhere, so much fun.

You'd be surprised how little of a vacuum leak can mess with your HVAC especially when climbing a hill. A previous owner had used a rubber vacuum "T" to connect a broken line and had plugged an unused port with a screw. That was enough to leak a significant amount of vacuum under a load.

P0171 indicates you're running lean on only one side of the engine (bank 1, passenger side). That code is more likely an intake manifold gasket leak.

 

[SCopeland]

You'd be surprised how little of a vacuum leak can mess with your HVAC especially when climbing a hill. A previous owner had used a rubber vacuum "T" to connect a broken line and had plugged an unused port with a screw. That was enough to leak a significant amount of vacuum under a load.

P0171 indicates you're running lean on only one side of the engine (bank 1, passenger side). That code is more likely an intake manifold gasket leak.

Interesting. To save myself some grief I'll probably still take it over to the shop tomorrow if time allows and see what they can find. I wish I could do it all myself, but living in an apartment complex makes it difficult. What is the likelihood of an intake manifold gasket leak causing both P0171/P0174? Is it more likely to cause one code than the other?

 

[koda2000]

Interesting. To save myself some grief I'll probably still take it over to the shop tomorrow if time allows and see what they can find. I wish I could do it all myself, but living in an apartment complex makes it difficult. What is the likelihood of an intake manifold gasket leak causing both P0171/P0174? Is it more likely to cause one code than the other?

All depends where it's leaking from, but I would think a manifold gasket leak would be more likely to show up on only one side, where something like a PCV grommet or hose leak would effect both sides causing P0171 and P0174.

 

[SCopeland]

All depends where it's leaking from, but I would think a manifold gasket leak would be more likely to show up on only one side, where something like a PCV grommet or hose leak would effect both sides causing P0171 and P0174.

Good to know. I'm gonna look more into this for sure.

 

[Batx00]

Thanks for all the info guys! Last night, I noticed the defrost won't fully shut off now. I pretty sure I have a vacuum leak somewhere. I need to check all the lines over, might be a crack in a hose that is getting bigger. Do the vacuum motors or panel switches wear out?

 

[koda2000]

Thanks for all the info guys! Last night, I noticed the defrost won't fully shut off now. I pretty sure I have a vacuum leak somewhere. I need to check all the lines over, might be a crack in a hose that is getting bigger. Do the vacuum motors or panel switches wear out?

Vacuum motors work buy creating a pressure differential on one side of a rubber diaphragm. It is possible for the diaphragm to crack over time and leak. As far as the HVAC switches, sure they can wear out over time, they were never designed to last forever. To test a vacuum motor you need a suction pump with a gauge to draw a vacuum on it, then see if the motor operates and holds a vacuum. You can purchase an inexpensive vacuum pump from Harbor Freight for probably around $10. It's a handy tool to have for lots of stuff (power brake boosters, bleeding brakes, checking EGR valves and any device that works on vacuum).

 

[Batx00]

Just to update everyone. I found the plastic shaft on the defrost/panel door is broken inside the heater box. The vacuum motor is working but end of the shaft would pop in and out when the motor was actuated. I have not tried taking the dash apart yet but at least I know what is wrong. I'll probably grab a heater box next time I'm in the junk yard.