Volvo 940 air conditioning fan blow to floor when accelerating

My 1994 Volvo 940, 4 cylinder (not turbo) air conditioner is acting
strangely. Normally, I set the air condition fan blowing from the front on
dashboard onto the face of driver and passenger.

When I accelerate the car, the fan switched blowing to the floor from the
bottom and stop blowing from the front on the dashboard.

All other electrical equipment seems to work.
The vacuum advance seems to be working correctly.
Can you tell me what is the problem? Thank you.

 

Additional finding:

After the local Volvo mechanic worked on the car for the last two days, they
were unable to find the exact problem. When they jack up the car, the air
conditioner and fan blower works well, both when engine idle and accelerate.
So they concluded the problem is not the vacuum control system.

Only when the car is on the road and accelerating, the air conditioner fan
will switch from blowing from top dashboard, to blowing from the floor
below. As soon as the car cease to accelerate in constant pace, the air
conditioner fan blows normally from the dashboard.

Strange? Any clue?

 

Get an inexpensive vacuum gauge and hook it up with a tee to a
suspected vac line under the dash. Place it where you can read it
while driving. You may need to move it from one line to another to
find the culprit. If it is a general vac fault, then select any line
and adjust the various temperature controls until vac is fed to that
line. The test drive and see if it dips when accelerating. if no, then
the problem is one of the vac motors and its related hose and
switching (I would assume) it the vac drops on all lines then the
problem is in the vac system.

...at least that's where I would go from there. But don't follow me..
I'm lost!
from Randy & Valerie
__ __
\ \ / /
\ \/ /
\__/olvo
1993 960 Estate

 

Subject: Re: Volvo 940 air conditioning fan blow to floor when accelerating

Sounds like a really good question for Car Talk.

 

The vacuum bellows which controls the push/pull blend door is faulty it
needs to be replaced it is the only vacuum bellows with 2 fittings on it
usually on the drivers side of the climate unit
Glenn

--
"*-344-*Never Forgotten"
Is for the New York City Firemen who lost their lives on September 11,2001.
The official count is 343, but there was also a volunteer who lost his life
aiding in the initial rescue efforts. And I will never forget them as long
as I live,
nor should any American.
"Mow Green"

 

This is 1994 Volvo 940 with single push button on/off air conditioner.
There is no temperature or climate control.

 

Where can I find Car Talk?

 

OK, after another day of work by the mechanics, this is still our problem:

When the car is not moving, everything works fine. Vaccum is fine.

When the car is moving at 25mph or faster AND accelerating, the fan will
switch from blowing from the top dashboard to below at the floor. As soon as
the car cease to accelerate and at constant pace, the fan switch back to
blow from the top.

Volvo 1994 940 6 cylinder (no turbo) automatic transmission, air
conditioning push button on/off switch without climate or temperature
control.

The fan seems to blow at same speed.
The air-conditioner on or off has the same problem.

 

Volvo 1994 940 6 cylinder...? I thought:
940 = 4cyl
960 = 6 cyl
whadooeye know?

As I mentioned before, it sounds like a control problem under the
dash- one possible scenario:

You have a weakly operating vac motor *1. When you accelerate the vac
lessens just enough that this vac motor 'relaxes' and is closing one
of the air-flow control doors. When you lift and system vac increases
the vac motor has enough force to open the door once again.


*1 - causes could be a cracked or disconnected vac line somewhere,
leaking vac motor diaphragm, etc.
from Randy & Valerie
__ __
\ \/ /
\__/olvo
1993 960 Estate

 

Randy,

Sorry, my mistake. This is 1994 940 with 4 cylinder.

Could this switch or flap caused by the momentem of the acceleration
movement that push this switch from blowing to top than to bottom? Where
could this be? Any picture?

Thank you.

 

I really don't know for sure. Maybe one of the gurus who knows this
car can say for sure. I would definitely start with the tip I gave
about checking the vac under real-time conditions- connect a vac gauge
to a line under the dash and drive and see what is really happening.

from Randy & Valerie
__ __
\ \/ /
\__/olvo
1993 960 Estate

 

You may have a 93 control unit. They are no longer avilable. There was a
problem with them.

 

What is the name of control unit?
Is this on the center top row on the dashboard with 3 turn knobs (fan speed,
blower up/bottom direction, and temperature) and two push buttons
(recirculation, air condition) ?
Where can I buy used or refurbish or replacement unit? How much does it
costs? Any way to repair it?
Thank you.

 

The vacuum motor is faulty & needs to be replaced this is the one with 2
lines going in to it under the dash on the left side of the climate unit
will post part # Monday night
Glenn

--
"*-344-*Never Forgotten"
Is for the New York City Firemen who lost their lives on September 11,2001.
The official count is 343, but there was also a volunteer who lost his life
aiding in the initial rescue efforts. And I will never forget them as long
as I live,
nor should any American.
"Mow Green"

 

OK, thank you. Is this part of the entire control unit?
Is this on the center top row on the dashboard with 3 turn knobs (fan speed,
blower up/bottom direction, and temperature) and two push buttons
(recirculation, air condition) ?

Is it possible for a picture of this?

Where can I buy used or refurbish or replacement unit? Any way to repair it?

 

The part is not very expensive but the labor to change it is up there if
you are a do it yourself person it is an all day job if you are not a do it
yourself person then shop around between the Volvo dealer & your local Volvo
specialist to see has the better price both time & hourly rate
Glenn

--
"*-344-*Never Forgotten"
Is for the New York City Firemen who lost their lives on September 11,2001.
The official count is 343, but there was also a volunteer who lost his life
aiding in the initial rescue efforts. And I will never forget them as long
as I live,
nor should any American.
"Mow Green"

 

Please post more detail of this vacuum motor?
Thank you very much.

 

The info ytou are looking for is here:
http://tinyurl.com/25z3b

Specifically, I think that this will/may answer the questions:
http://tinyurl.com/3fdau

__ __
Randy & \ \/ /alerie's
\__/olvo
'93 960 Estate

 

OK, further repair report. But saddly still same problem.

The mechanic replaced the entire dashboard control unit.

This is the control unit on the center top row dashboard console.
This control unit has 3 large turn knobs (fan speed, blower direction,
temperature) and two smaller push buttons for recirculation &
air-conditioning. Behind the middle large turn knobs for blower direction,
its actually a white plastic square box with vacuum nozzles. I assume that's
how Volvo uses vacuum to control the blower direction to top or bottom.

After this control unit is replaced, the air blow works normal inside the
garage when the car is stationary. However, when the car is moving at least
25mph or faster and during acceleration, the fan blowing slows down and
switch from blowing from the top to the bottom of the car. The blower switch
back to top when stop accelerating.

We are unable to find any vacuum leak anywhere.

 

The first place to check is the double acting vac motor located at the
driver's foot well, up against the right side of the well, on the
large black climate control box/whatever. Remove the cover there and
you will see it. It has two vac lines going to it. One side is
probably leaking. This can easily be checked with a mighty-vac tester.
This unit is famous for its failure rate. One side will hold vac and
the other side will not. The replacement involves either removing the
dash and disassembling the temp control box (whatever it is called) or
just cutting a hole i the face of the box and then putting a plastic
patch over the hols when done.
__ __
Randy & \ \/ /alerie's
\__/olvo
'93 960 Estate