air vents cut out under load

  • Thread starter Thread starter rgarrett
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rgarrett

When accelerating or climbing a hill, the climate control of my '93 960
changes from the dash vents to the floor vents until the vacuum rebuilds. I
have searched and searched for a vacuum leak. Both black/white vacuum check
valves on the firewall have been replaced. The cruise control works
perfectly so that portion of the system is fine. The brake booster check
valves is fine. The brakes do pulse a little, maybe the vacuum leak, maybe
warped rotors. This was always a cinch to fix on the 740's. Does anyone
have experience correcting this symptom on the 960? Thanks.
 
rgarrett said:
When accelerating or climbing a hill, the climate control of my '93 960
changes from the dash vents to the floor vents until the vacuum rebuilds. I
have searched and searched for a vacuum leak. Both black/white vacuum check
valves on the firewall have been replaced.
Click to expand...
Have you checked the double acting vacuum motor on the driver's side
of the center console behind the cover on the right side of the
driver's foot well? These are notorious for leaking and a pain to
change unless you cut into the heat/cooling plastic box thingy. It's
one of the few _really_ stupid things I have foind on the 960. That
and the design of the PNP switch- but at least you don't have to
disassemble the tranny to get to that.
The cruise control works
perfectly so that portion of the system is fine.
Click to expand...
The cruise control is powered by a vacuum pump that is electric and
not at all related to engine manifold vacuum.
The brake booster check
valves is fine.
Click to expand...
That has a one-way valve, so once a vacuum is built up it is (or
should be) held for long periods if the brakes aren't used, and since
you rarely use the brakes (use the vacuum booster) when accelerating
(when vacuum is the lowest) it usually won't show as a symptom.
The brakes do pulse a little, maybe the vacuum leak, maybe
warped rotors.
Click to expand...
Probably warped rotors.


__ __
Randy & \ \/ /alerie's
\__/olvos
'90 245 Estate - '93 965 Estate
"Shelby" & "Kate"
 
It is supposed to do that to lessen the load on the engine so try not
putting the pedal to the metal so hard.

All the best, Peter.
 
Peter K L Milnes said:
It is supposed to do that to lessen the load on the engine so try not
putting the pedal to the metal so hard.

All the best, Peter.
Click to expand...


Huh? Mine never did that, though it did just start doing the exact same
thing recently, it's clearly a vacuum leak as the system should hold a
vacuum indefinitly even if the engine isn't running.
 
James said:
Huh? Mine never did that, though it did just start doing the exact same
thing recently, it's clearly a vacuum leak as the system should hold a
vacuum indefinitly even if the engine isn't running.
Click to expand...

You'll find if you take the hose off the leaking side of the double
acting servo and plug it, that the system will work fairly well until
you get around to fixing it properly.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Mike F said:
You'll find if you take the hose off the leaking side of the double
acting servo and plug it, that the system will work fairly well until
you get around to fixing it properly.
Click to expand...


Is this true of a 740 as well? I haven't done any investigation yet, been
too busy with house projects to worry if my vents blow on hills.
 
The 740's have a manual climate control system. The most common reason the
air will come out the defroster vents instead of the dash vents is a rubber
plug on an unused port in the vacuum reservoir. If I remember correctly,
the reservoir is tucked behind the front bumper. The rubber plug cracks
over time. With little or no vacuum, the climate control switches to the
default vent mode of defrost for safety reasons. If the crack is large
enough or the plug falls off, air comes out the defroster vents all the
time.
 
James said:
Is this true of a 740 as well? I haven't done any investigation yet, been
too busy with house projects to worry if my vents blow on hills.
Click to expand...

The 740 system is completely different, and I've not had to look for a
vacuum leak on it. So then answer is, I don't know, maybe.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
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