1990 740 GL - No air from blower, with any setting

I have a 1990 740GL that has no air flow from the heater/ac vents. It
does not matter what setting I set the sliders for, no air comes out.
Hot or cold, Defrost or floor or face. Not even enough to move a
tissue.

The blower motor was making a ton of noise on speed 4, so I replaced
it, hoping that was the issue. No luck! It is however now allot
quieter.

On the passengers side of the heater box is a little panel that can
be removed, that appears to hold some sort of pre-heater. With this
panel off, the blower will push enough air out this hole to rustle a
newspaper in the back seat.

I can hear the vacuum hiss while moving the control levers, and the
vacuum supply going through the firewall is strong on the engine side.
I can also watch the 'actuator' on the upper passengers side of the
heater box move when the heater selector lever is moved from floor to
defrost.

Any pointers?

Charlie

 

You've got a vacuum leak somewhere, find the source of that hiss and you
will probably find your problem.

 

That was my first thought, but should it not continue to hiss if that
was the problem? The hissing only lasts a few seconds. I assumed
that was one of the 'actuators' having the air sucked out of it. I
ask because my Suburban does the same sort hiss as the slides are
moved. But the air flows as directed in that.

 

Ah, I thought the hissing continued. Well somewhere one of the flaps is
not opening, I've never dug into the vent system in a 700 enough to know
exactly what.

 

If the fan only works on # 4 setting, the fan resistor is bad. If the
fan sounds like it is working, but air is only coming out of the
defrost, then you have a vacuum leak.

 

From what I found... Nothing... Everything seems operational. So
I'm guessing an obstruction someplace.

Any 'best practice' ways of going about looking for this possibilty?

Charlie

 

Do you have a Haynes manual for the car? It should show the layout of
the ventilation system. One of the flaps somewhere must not be opening,
I don't see how any foreign object large enough to cause that could get
in there.

 

No manual, well I have the Chilton®. Wow does that guide ever suck!

Think I need to just pull it out and tear in? Seems like a ton of
effort, but it's getting COLD out!

 

Chilton manuals are worthless, they try to cover too many cars in one
book. Haynes isn't perfect but it's much better. If I think about it
I'll look in my manual when I'm home.

 

I bought this car 3rd hand. So I only have the history the prior
owner gave, very little.

The cowl (is that the term for the area the windshield wipers are
in?) would seem to have a screen under it. That screen has a small
(mouse?) hole in it.

While removing / replacing the blower motor, I could see no signs
of foreign items.

Would it be safe to 'snake' a piece of wire down through the cowl? I
do not wish to puncture anything, and I'm unsure of the exact location
of the heater core. Is this even wise?

 

Fan works for all settings.

No air comes from any vent, regardless of vent selector or temp
selector position.

I'd be pleased to have just the defrost, or any other vent, but all I
get is the slightest hint of hot or cold air depending upon temp
selection.

Oh, and yes the 'hint' of air does follow the vent selection. If I
select defrost, the 'hint' of air seeps out of the defrost. If I
select face, the 'hint' of air seeps out the front vents.

If I select floor, I can't feel any air.

 

This link may be of interest...

http://www.swedishbricks.net/700900FAQ/HeatingAirConditioning1.html#Heating and Air Conditioning

 

Charlie,

Just the info I was waiting for!
So, the shutters seem to be working OK, the speed selector (therefore
the resistor pack), seems to be working OK, the motor is running OK.
Seems to leave only one thing easy thing to check; don't laugh, is the
motor rotating in the correct direction?
And one difficult thing to check - that being the pollen filter, which I
have no experience with.
I changed the motor in my 740GL for an apparently identical one from a
Volvo used spares dealer; the fan was identical, the motor housing was
identical, but, it turned out the motor was wound so that it ran
backwards when the feed terminals were properly (for my car) connected.
The motor ran, but, not much air came out of the vents, and it seemed a
bit noisier than it should have been, so, I swapped the feed terminals +
to - and - to +, and lo! Loads of lovely quiet air promptly emerged, and
x number of years latter it's still going strong.
See if you can safely run the motor (speed 1 or 2) without it being
installed in the heater, I can't remember if they have a direction
marked on them, but, when running in the right direction it will
centrifugally fling off loads of air, the wrong way results in the slats
of the fan basket acting like scoops trying vainly to force air back to
the centre of the fan basket.
Can't explain any better, sorry, but, I could tell just by looking at
one though LOL!

Best wishes,
Ken Phillips

 

If there's an archive of this newsgroup you might go back about 3-4
years when I had similar problems with a 760GL: winter was almost upon
me and I could hear the fan motor working hard but no air was coming
out!

Here's my advice (because it's what I found was the problem with
mine):

Remove the blower motor and reach into the opening and feel to your
left for the evaporator (a fine grille of fins that are part of the
air conditioner). It should feel like the face of your radiator but
it may feel like a solid rubbery wall.

At the point I'm describing the air from the fan is expected to pass
through the evaporator and cooled/dried. In my case we surmised that
the previous owner added some leak-stopping substance to the
pressurized AC system and it leaked out from a hole in the evaporator
and coated the fins. Over time dirt and general crud collected on the
sticky surface (no pre-filter on the air intake in these older models)
and eventually gummed the whole thing shut.

In my case I simply accepted that I wouldn't have AC and wrenched the
offending part out (and many other ancillary AC components that were
not needed) and the air blew through the duct system like a gale!
Eureka!

The thread from trying to diagnose this problem was at least 35 posts.
I checked fuses, vacuum lines, wiring, solenoids, electronics with a
voltmeter, etc. etc.. My first assumption was that some
vacuum-controlled gate was stuck shut but after I pulled out the
evaporator everything else worked flawlessly!

I still have a pile of details from the 760 and suspect that, while
there may be positional differences, most of the components will be
the same. Let me know if you'd like me to email you the whole bundle
but first check that evaporator!

Good luck,
blurp

 

Thanks, that was informational. It also seems to fit my issue. I
was able to view the evaporator when replacing the blower, but at that
point I was only looking for the obvious squirrel nest or other debris
and remnants.

I have a little access panel between the blower and the evaporator,
that when removed the air comes out at the expected high rate. Of
course it's just the outside air I believe, so just leaving that off
is no help

 

Thanks for the heads up on the spin direction. I will triple check
this. The 'original' two connecter plug has been replaced with crimp
connectors and spade plugs to connect the motor. I'm assuming some
one did a quick/cheap fix on the blower in the past. I just plugged
the new one in 'same as it came off', but who's to say that was
correct...

 

That really does sound like a vacuum leak somewhere, IIRC the flaps are
all opened by vacuum and default to closed. When I had a split in the
cap of the vacuum accumulator, my vents would close whenever the turbo
spooled up enough to create some positive pressure in the manifold. What
I would recommend next is find a place where you can see one of the
vacuum servos, you should be able to look up under the dash with the
footwell covers removed. Move the vent selector with the engine running
and see if the servo moves the flap, then you'll know if it's a problem
with the fan, blockage, or the vacuum system.

 

Do you know how many 'flaps' there may be?

I know that a lever (I assume is connected to an internal flap)
behind and above the glove box moves in sync the defrost/floor/center
lever. Does this control fresh air possibly?

I was also able to view the movement of a 2nd lever that was behind
and slightly to the left of the radio/center console.

I don't know if there is a min. amount of travel expected, but they
would seem to move a good amount, and do not seem to be jumpy or
sticky.

Now if only the duct work were clear... (Or I had x-ray vision)

Thank you all for your input!

 

Well try moving them by hand, the vacuum servos are really simple
devices, they're just a cup capped with a rubber bladder that has a
fitting on it for the lever to attach. Pull a vacuum and the bladder
contracts into the cup and pulls the lever. Moving it by hand should
allow roughly the same travel. I don't know how many there are, I've
never ripped one apart, but the fact that some of them do move does
point more towards the fan, then again, you said opening something
caused air to rush out.

 

Yea, there is a small oval panel with a electrical connector on it.
The back of this panel has three coils that get REAL HOT and are
inserted into the heaterbox. Some sort of preheater? It is screwed to
the Heater box between the blower motor and what I believe is the AC
evaporator. When removed, I can see the blower 'wheel' on the
right, and the evaporator? on the left.

With this panel off there is a good deal of air flow. (Out the hole
that the panel was covering) So I suspect the blower is functioning
properly, but as blurp said a little earlier, the air may not be
passing through the evaporator, or whatever is on the other side of
that. It would seem possible since that is the only direction for
the flow to go. More investigating is order I guess.