Recirc vent will not cycle

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
Out of nowhere,the '96 Passat Wagon's recirc air vent stopped cycling.
It was working yesterday and today I just heard a slight mechanical sound behind the dash as I tried to get it to recirc inside..
Last summer I found the hose behind the battery worn through. This time it seems to be something else altogether.
Any ideas as to what may have happened?
How do I get to the location behind the dash?
Any test I can do?
Thanks.
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
Find the vacuum solenoid inside the drivers fender, and apply vacuum to it with a MityVac or similar, and see if that moves the recirc door. If not, then the door actuator is bad, or the line going to it has an open somewhere (it goes through a plastic nipple between the heater core hoses at the firewall).

If so, run the car and see if you have vacuum at the other line going to the solenoid (one goes to the door actuator, the other supplies vacuum from the vac pump.

If that checks out, get a test light and see if you have power and ground at the solenoid when the dash button is pressed.

If all that checks out then you likely have a bad solenoid.
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
Is the vacuum solenoid the one behind the battery? It goes to the engine and then back to the firewall.
When I press the recirc I hear something trying to cycle but the door does not move.
The locks are working normally.
If the dashpot/actuator is broken,how do I get to it behind the dash?
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
Yes that's the one.

You can get to the actuator from the passenger's footwell - it's tight, but you can see it there against outside of the car.

You can also see the door (if it moves) from the outside through the raid tray if you remove the cabin air filter.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Is the vacuum solenoid the one behind the battery? It goes to the engine and then back to the firewall.
When I press the recirc I hear something trying to cycle but the door does not move.
The locks are working normally.
If the dashpot/actuator is broken,how do I get to it behind the dash?
The central locking system is on a different circuit. The actuator that controls the recirc door is under the glovebox next to the right kick panel. The switchover valve that turns vacuum on and off to the actuator is behind the battery in the engine compartment. It's an electrical valve like the N75.

There should be a nylon vacuum tube running from the switchover valve back and around to where the heater core comes through the cowl. Between the two heater hoses there will be a small nipple that the nylon tube connects to via a rubber hose. That in turn connects to a hose inside the car that runs down to the servo under the dash.

If you think the actuator is bad you can tap into the vacuum line under the hood with a hand vac pump and apply vacuum. If the door actuates as it normally should when in the AC Max position then the fault lies elsewhere. If it doesn't respond to vacuum then you might want to investigate whether there's a fault with the vacuum tubing or with the switchover valve.

Steve
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
I did several test this morning and here are the results:
The solenoid valve works and there is 12 volts at the plug. you can blow through it with no effort.
The lines were OK except for the cloth one going through the firewall between the two heater hoses. It was dry rot at the bulkhead. I cannot get the the inside of the firewall to fully replace this hose which can only be a short piece since the vacuum hose going to the dashpot is of a diff type altogether. I installed a hose barb and a new short piece of vacuum line and it seems to be OK.
If I pull up on the "flapper" that changes outside/inside air the flapper will close. It will NOT do it by itself.
I put a vacuum gauge in the supply vacuum hose at the dashpot nipple and it shows 16" of mercury suction.
Is this normal? or way too low?
If you think the dashpot is bad,how do you remove it? I have the knee pad and the air bag removed so far on the passenger side.
The shiftier consul and arm rest is off as well.
I'd like to replace that cloth hose through the firewall but have no idea as to how to get to it behind the dashboard.
Thank you for your help so far.
 
Last edited:

kooyajerms

grocery getter
Joined
May 5, 2004
Location
Pomona, Southern California
TDI
97 B4V (mine), 11 x5 35d (hers) 04 V10 (that one you want), 2014 Q7 (mom's) 74 Shasta 1400
http://forums.tdiclub.com/showthread.php?t=321307&highlight=vacuum this was an old thread

tried my darnedest to find a a picture of the diaphragm.

You need the smallest right angle phillips or angled drivers. its behind the actuator, feel around with your fingertips.

This solved my lack of recirc. Actuator wouldn't hold vacuum when I used the Mityvac.
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
This is getting stranger now.
The vacuum gauge is reading 16" at the actuator. 18" at the engine.
If I run a vacuum line from the engine to the dashpot,it cycles as it should.
If I hook it up to the solenoid it will not cycle even though it shows 16" of vacuum.
If I run a vacuum line to a "hose barb" at the firewall, the dashpot will not cycle.
I'm not sure what you are saying about removing the dashpot. I used a mirror to try to see the screws you mention by I see none.
I'm pretty sure the vacuum line between the heater hoses is rotten. I have no idea as to how to remove it. I cannot get to the inside firewall side*.
Here is what I've found out.
The 12 volt solenoid behind the battery is working-16" of vacuum
The vacuum line from it to the white plastic line has been replaced with new.
The white plastic vacuum line has been blown out with brake cleaner.
16" of vacuum at the far end of the white plastic line when the solenoid is on.
Hook up to the firewall vacuum line going into the car, no cycling of the flapper.
There has to be some sort of fitting just on the inside of the firewall. The hose type changes from fabric covered to smooth rubber going to the dashpot. Any idea what/where that may be located?
Any idea what the part number is for the solenoid behind the battery? It seems to be working but it is very old.
*I have to get to that vacuum line behind the dashboard. I can't figure out how/what to remove to get to it. The airbag support bracket is in the way and will not unbolt without removing the whole dashboard. There has to be a hidden screw up on top of it.
I thought I hard the bottom portion of the dashpot hissing a little, not sure though between the fan blowing and the engine running its hard to hear clearly.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
You're going to need to pull the dash to get to the cabin side of the nipple. The heater core bulkhead is what the barbs are connected to.

Personally, as a test, I'd run a temporary vacuum line from the recirculate solenoid to the vacuum can. Run it outside the car and in through the window.

If it moves, just find another hole in the firewall to get the vacuum line through.

-Todd
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
There is a grommet on the driver's side that you could get a vac line through.

Also, have you tried revving up the engine? The vac pump will likely produce a higher vacuum when you raise the engine above idle.

If that's the case, you might be OK - the vacuum may be alright to get the door to close off idle and keep it there.
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
I may have to run a new vacuum line for sure. I do not know what the specs are on the VW vacuum pump. I'm not sure how many inches of HG a new pump would pull?
Mine is making 18" inches max. It seems to keep the same from idle to full RPM.
I will double check it in the morning.
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
The other thing to check is if the actuator and lines hold a vacuum without bleeding down - if the vac does not hold, it will take more vacuum to get the actuator to move.

If it were mine, I would run a new line, avoiding the restrictive nipple through the firewall. Only then (if it still did not work) would I consider replacing or servicing the vacuum pump.
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
Is there a nipple at the firewall? I have no drawings or photos of the bulkhead connector.
I still may have a weak vacuum pump. It will only put out 18" of HG at any speed.
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
From the factory, there is a plastic nipple on the firewall between the heater hose connections where the switched vac source to the recirc door actuator goes inside the car.

If you avoid the nipple (and its restriction) you may get to the point where your marginal vac pump output is sufficient for the recirc door to work properly.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
I've never heard of a vane type vacuum pump kicking the bucket, that's just really unusual in my book.

The dash center section might need to come out to get to the inside section of the hose. You might be able to get to it via the radio slot but I think the upper dash vents are still in the way. As others have said there is a nipple on the inside at the hose connections just like in the engine bay.

If the electric switchover valve is working don't worry about it, I'm using one from 1990 and it's still doing a fine job on the B3V.

I had pictures of my AC box installed but with P-bucket now prohibiting use of pics on other sites, I cannot show it here at the moment.

I'm with Todd on this one. As much as I like a factory connection I think in terms of expediency you will want to just maybe bypass the original hose and run a new vacuum line from the actuator out to the switchover valve. If you want to diagnose further later on you can do so but getting it operational is the priority.

Steve
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
The radio is blocked from the behind by a sheet metal enclosure,thrills.
My vacuum pump is only providing 18" of HG. While I cannot find ANYWHERE the specs on the pump,what post I have found show 25-30" of HG seems to be normal.
If I run the flapper directly from the engine it works like a champ at 18". If I run it directly off of the solenoid valve to the flapper it will not cycle. There is a slight drop in suction,I'm thinking volume of suction,not the real inches of HG.
I took the valve apart and cleaned it. It was not bad inside at all. It cycles with a battery and flow is unrestricted. Size matters,Ha.
I will prob do the bypass hose.
I have a new problem now that I have to figure out. My AC compressor will not turn on.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
The radio is blocked from the behind by a sheet metal enclosure,thrills.
My vacuum pump is only providing 18" of HG. While I cannot find ANYWHERE the specs on the pump,what post I have found show 25-30" of HG seems to be normal.
If I run the flapper directly from the engine it works like a champ at 18". If I run it directly off of the solenoid valve to the flapper it will not cycle. There is a slight drop in suction,I'm thinking volume of suction,not the real inches of HG.
I took the valve apart and cleaned it. It was not bad inside at all. It cycles with a battery and flow is unrestricted. Size matters,Ha.
I will prob do the bypass hose.
I have a new problem now that I have to figure out. My AC compressor will not turn on.
Interesting, you know, if your AC won't run I don't know whether the valve will actually allow vacuum to the recirc door or not. That could explain why you're not getting any action from the door.

Steve
 

Rapidrob

Veteran Member
Joined
Jun 20, 2004
Location
Edgewood,New Mexico
TDI
96' Passat Wagon
I will have to do another test before I spend a lot of money on a new pump.
I need to buy an adapter to fit the primary vacuum hose ( 14mm?) and drop down to my vacuum gauge hose size for a reading.
I'm not sure is my brake servo is leaking or not. I have good brakes now and they hold well.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Interesting, you know, if your AC won't run I don't know whether the valve will actually allow vacuum to the recirc door or not. That could explain why you're not getting any action from the door.

Steve

I think it does. There's times when I recirculate when sitting in traffic. This way, I'm not pulling in exhaust fumes.

-Todd
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
I think it does. There's times when I recirculate when sitting in traffic. This way, I'm not pulling in exhaust fumes.

-Todd
So your recirc button does not also engage the max AC? I know on the Mk3 that recirc is a separate function but on my B3V you have to run AC to get recirc. I had assumed that they kept that the same with the B4.

My B3V AC was totally replaced with B4 stuff except I think for the control head in the car which came from another B3. If I want the recirc door closed to outside air I have to run the AC. If the fan is off then the door won't close. Said another way if the AC won't run I don't think the door will close either.

Very curious about this...

Steve
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Isn't Max AC just when the AC system is on and the car is recirculating? If so, then yes.

Otherwise, as mentioned, you can also recirculate, without the AC running.

-Todd
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
On my B4 the recirc works any time the fan is on. There is no MAX or Desert setting.
Isn't Max AC just when the AC system is on and the car is recirculating? If so, then yes.

Otherwise, as mentioned, you can also recirculate, without the AC running.

-Todd
So the B4 is just like the MK3 then. In the B3 there's two buttons just like the B4 but one is Norm AC the other is Max AC. The choice is one or the other not both. If you want recirculate you have to turn on Max AC, otherwise it takes in outside air by default.

On another note the recirculate door does work with the fan off, but doesn't really count for much.

I should check the part numbers on the control head and see whether there was a change for the B4. I would think there would have to be a difference.

Steve
 
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