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1994 Recirc Door (kinda long)

massacre

Elite Explorer
Joined
January 24, 2018
Messages
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City, State
Massachusetts
Year, Model & Trim Level
‘94 Explorer
‘19 Nautilus
So I am starting a new thread on this subject, continued from a previous thread.

I have been hearing a slight hiss under the dash since I got the truck, but everything seemed to be working ok so I never really thought about it. I recently cleaned out my heater box, and did some heat-related diagnostics which ended up being a stuck thermostat.
In the process of the diagnosis, I realized that my recirc door is not opening when it should.
When I thought about it, it makes sense as it never seemed like the truck ever really got fresh air in the cabin without putting the window down. It is a factory AC truck, but I need to repair that system so it is not being used.

So, i am now trying to diagnose the vacuum lines.
It appears that vacuum comes into the cabin through a black vac line that originates at that check valve. This line goes all the way to the heater control assembly.
I am testing the lines with a vacuum pump, and different sized fittings and plugs. Basically plug one end, pull a vacuum on the other end and see if it will pull and hold a vacuum and listening/watching for leaks.
first step, apply vacuum to the recirc door actuator. Pulled and held a vacuum.
Black line coming into the cab to the heater control assembly, pulled and held vacuum. There is a “vacuum actuator” that seems to route the vacuum from the black vac line from the check valve under the hood, to a white vacuum line that goes to the recirc door actuator.
White vacuum line also pulls and holds vacuum.
The white vacuum line attaches to the recirc door actuator with a tee fitting, and the other side of that fitting attaches to an orange vacuum line that ends up attaching to the top of the intake air box cover.

After testing all the lines separately, it was time to start reattaching the lines and continue testing.
I made a jumper hose to jump out the “vacuum actuator” at the heater control assembly, and send vacuum directly to the white vacuum line, and hooked up the tee fitting to the recirc door actuator.
No joy, would not pull a vacuum.
So I removed the orange line from the intake air box lid, and plugged It. I was able to pull a vacuum from the black line at the check valve, and then could build a vacuum, and it held. the recirc door actuator worked, and the door opened.

This is good info, as it narrows things down quite a bit.
From hearing the slight hiss, I wonder if the “vacuum actuator” was not applying good vacuum to the actuator?
I will remove the heater control assembly from the truck, since the “vacuum actuator” ended up falling out and I need to reinstall that.

My question is does anyone know why that orange vac line goes to the intake air box lid? There is also a black vac line that attaches right next to it.
Almost like if I just plug that line, it should work fine?
I need to do some more research, take the lid off and see what is going on there. I suppose the check valve could also be bad, etc
but diagnosis is all about ruling things out, and it looks like everything beyond the check valve and in the cabin is mostly good.
I’ll reassemble the “vacuum actuator and test it’s operation Which should rule that out.
If I can get the heater control assembly working, then I can put the dash back together, plug that orange line and have a functioning recirc door. Then I can start testing everything from the check valve back.
 



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iirc:
orange out to engine bay connects to bypass valve that is on my 94. Vacuum to the bimetal valve on the intake air box should come straight from the vacuum tree, not the orange. I believe vacuum to the orange only exists when "Max AC" is selected. Possibly "off" position as well. don't recall atm.

Also, when the vacuum is not/insufficiently applied to the vacuum actuator, that lets the fresh air in. When vacuum is applied, cabin air is recirculated.
 






I am unsure about this but i would assume that if it hooked to the intake box that should be some sort of a vacuum or air flow regulator of some sort. I dont know mine does not have that and my 94 ranger had the 4.0.
 






I've been working on a 94 I bought back in November. Orange hose on mine goes to the water bypass valve & moves the valve when controls are on max a/c.

Your threads are very helpful to me right now since I'm chasing down all this stuff as well. I'll be switching out the controls this week and looking for ways to get good flow to the rear heat register.......hope you hit on that at some point.
 






Thank you for this info! ^^^

Every vacuum diagram I see shows the same thing- the orange going to the heater control valve.

I am looking at the “vacuum actuator” and it looks like a simple shuttle valve.
The door stays in the same position no matter what setting it is on.
 






Couldn’t sleep so decided to do a little more investigation.
The “vacuum actuator“ is basically a plastic block with a button, that slides up and down on a spring. The position lever (off, floor, defroster, etc) is bent, and sliding the position from right to left pushes down on the button and controls the height of the plastic block. In “off“ and “max Ac“ position, the button (and the plastic block) is pressed down. In other positions, the button (and the block) are left in the up position.

The plastic block looks to have a small rubber surface on a small plate with a spring behind it. I wasn’t getting a good seal, so I pried out that plate, found the parts on the floor after they went flying lmao.
I stretched that spring out a little bit and reinstalled, the increased pressure was now making a good seal, and the switch is now pulling and holding vacuum. When I press the button, the vacuum bleeds off to the other side of the switch.
Sorry I left my phone upstairs and didn’t feel like waking up my wife to go get it, so no internal pics of the switch unfortunately. But I could draw it out on paper if anyone needs. It seems like the switch is functioning properly now.

Which leads me to another question-
When the “position switch” (off, max AC, panel, floor, defrost, etc) is the “off” position, the recirc door is supposed to be closed, correct? Which is the same as “max AC” as far as that vacuum switch is concerned, both positions leave the switch in the ”down” position.

From what I am reading on here, in the “max AC” position, the recirc door should remain closed to fresh air. This means that the vacuum switch should allow vacuum to be pulled on the white vac line to the recirc door actuator, as well as the orange line that should go to the heater control valve to divert coolant on max AC setting.
Is this correct? It seems to make the most sense.

Except am I the only one who finds it odd that the same vacuum is being pulled in the “off” position?
So when I shut the heat off and turn the truck off, the only thing keeping that door closed to fresh air is vacuum? Does it bleed off? Does the check valve prevent it from bleeding off?

There is no vacuum being pulled there, and it is looking like it might be because of some bad vac line routing.
My truck has always had the orange vac line attached to the air box lid since I have owned it. I have a feeling that if I just attach the orange vac line to the heater core coolant diverter valve, that might solve this whole issue.

There def was a hissing under the dash, and I think that was the vacuum switch leaking so glad that is fixed.
gonna try and put everything back together and test some more
 






So I installed the rebuilt vacuum switch onto the heater control assembly and hooked up the harness with the white/black vacuum lines. In the “off” position, I can pull a vacuum (slowly) and the recirc door will close, with the orange vac line plugged. The rubber end on the orange vac line is too large to fit onto the heater core recirc diverter valve. So that sucks lol.
If I move the selector switch to any other position, the vacuum will bleed off and the recirc door opens. And I get that same hissing that I was hearing under the dash. Except I was hearing the hiss at all times (except in max AC or Off positions)
My guess is that vacuum valve was leaking and not sending proper vacuum to the recirc door. Plus the potential leak on that orange vac line.
So it seems like I can get the system to operate correctly with my vacuum pump, which is encouraging.
That still doesn’t explain the orange vac line but I don’t mind plugging that for now to reassess that part later.
The recirc door actuator seems kinda slow to close, might even replace that if I can find a new part.

Gonna put everything back together and see if it will work after that.
 






That's very good information. I've many times thought about upgrading my AC system to add a control for the recirculate door. I think for many vehicles, a switch could be added for just that one function. The basic simple vacuum switch is a key, some like the Explorers have that, and others it's more complicated, built into the main AC control unit etc.

I like it to recirculate most of the time, to reduce outside smells, such as at every intersection we stop at. If you had a switch, a button, hit it when you want to, like seeing a dead skunk in the road up ahead.
 






So put everything back together. Start the truck, and in the off position, the recirc door closes to outside air under engine vacuum. Change positions, and the recirc door will open to outside air as the vacuum bleeds off at the vacuum switch. It takes about 20 seconds but it is working now.
So that rules out a bad check valve I would think.

Now I have to change my attack and look into the orange vacuum line and what is going on with the airbox lid, and the 2 vacuum connectons there. 1 of the connections is from the main vacuum harness, black plastic line.
I’ll pop the lid off, I think I remember seeing something on the underside of the lid last time I had it off.

The vacuum connection to the heater core diverter valve on my truck, is connected to the heat riser valve in the plastic intake tract before the air box. When I apply vacuum to that heat riser valve, it pulls and holds vacuum and the flapper moves. So doesn’t seem like there are any leaks there. I gotta climb under and see where that vacuum circuit originates.

So a couple more areas to inspect, but at least I was able to get the recirc door to close to outside air in the off position. That was my goal to try and keep the mice out. IDK if that will even work for the mice, but no more hissing under the dash either, which was a small vacuum leak.

This may have also solved the problem of air coming through the vents in the off position, which would be nice.
 






the recirc door closes.. takes about 20 seconds but it is working now.
So that rules out a bad check valve I would think.
not necessarily . The position of the ball in the check valve can change from a "good spot" to a "bad spot". The best way I have found to test that check valve (the one just after the vacuum reservoir) is to remove it, very gently suck on the air-flow-input end (sealing one port if it is the "t" style). Rattle it a bit and repeat, a couple times. If at any time it doesn't completely seal, it's bad. It should seal under very little suction force.

The rubber end on the orange vac line is too large to fit onto the heater core recirc diverter valve
The rubber grommet on the end of my orange line is does have a large outside diameter , but still fits snugly on the diverter. ( note:my check valve is currently blocked off. Original black tube finally cracked couple days ago, waiting for replacement to arrive)
yyNbWi8.jpg


The vacuum connection to the heater core diverter valve on my truck, is connected to the heat riser valve
That, should not be. Riser valve should be connected to the other connection of bimetal valve on intake box.
 






Here is a pic of my air box lid, and the 2 connections there.

PAtHY2.jpg
 






Here is a pic of my air box lid, and the 2 connections there.

View attachment 327042
Yeah, I think thatorientation is just going to cause a vacuum/pressure neutralizing effect at cold start. Your heat riser is taken out of the circuit completely, and so is your diverter.
 






not necessarily . The position of the ball in the check valve can change from a "good spot" to a "bad spot". The best way I have found to test that check valve (the one just after the vacuum reservoir) is to remove it, very gently suck on the air-flow-input end (sealing one port if it is the "t" style). Rattle it a bit and repeat, a couple times. If at any time it doesn't completely seal, it's bad. It should seal under very little suction force.


The rubber grommet on the end of my orange line is does have a large outside diameter , but still fits snugly on the diverter. ( note:my check valve is currently blocked off. Original black tube finally cracked couple days ago, waiting for replacement to arrive)
View attachment 327041


That, should not be. Riser valve should be connected to the other connection of bimetal valve on intake box.

Thanks so much for that picture, very helpful!
I will try to route mine the way yours is and see how that works out.
The orange line is pretty big, so I may try an adaptor to see if I can get it to seal.
Really appreciate the help!
 






I was able to trim a little off the length of the rubber fitting on the orange vacuum line, and it seems to fit correctly on the diverter valve now. I rerouted the hoses to match what was shown.
Gonna load up the truck with trash and head to the dump and see how she works.
Will report back
Thanks
 






Lot of good info here! Good job! ill be working in my blower motor switch in the next few days i only have 1-2-4 Three has gone to the way side, I have already looked at the resistors at the blower motor and there fine and have replaced the blower as well.
 






Thank you ChildIdenticant!
You saved the day for sure!
The recirc door opens and closes when it is supposed to, the diverter valve opens and closes now, and no more air through the vents in the “off“ position, no more vacuum leak behind the dash!
Seems like everything is working great, thanks everyone for all the helpful advice!
 






qhVa2w.jpg


You can see all 3 lines ran properly in this pic
Sorry for the lighting my garage is a cave
 






You can see all 3 lines ran properly in this pic
Sorry for the lighting my garage is a cave
If you can manage it without stressing the line, I would try to orient the orange so it isn't resting against the hose carrying the hot coolant.
 






View attachment 327060

You can see all 3 lines ran properly in this pic
Sorry for the lighting my garage is a cave

It's fine, the plastic cover on the coolant hose is protecting the air cleaner and the vacuum hose, from excess heat.
 



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That is a great point, I’ll re-route it
Thanks
 






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