HVAC blend knob regularly cracks inside
Thread Starter
Joined: Jan 2002
Posts: 4,072
Likes: 75
From: Casselberry FL
HVAC blend **** regularly cracks inside Every year or so my HVAC blend **** cracks on the inside. The metal D-ring inside the clear tube appears to rotate, which causes the clear plastic tube to crack and flex, which in turns causes the **** to not work well. I've band aided this in the past with replacement *****, but I'm wondering if there's something else besides the **** in play here. What else could be causing this behavior other than poor **** quality?
Copy & Paste Moderator
Joined: Apr 2002
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From: Eastern MA
Either you are twisting too hard or the mechanism has gotten so stiff that you are needing to twist too hard. Its all mechanical cable driven. I guess you need to look for things to lube.
Thread Starter
Joined: Jan 2002
Posts: 4,072
Likes: 75
From: Casselberry FL
Even when I replace the **** it's still stiff to turn slowly compared to the other two *****. I vaguely remember that the HVAC controls are dependent upon vacuum. Could low vacuum, a vacuum leak, or not having my vacuum tank connected (broken line that was capped at the distribution point) be related?
Copy & Paste Moderator
Joined: Apr 2002
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From: Eastern MA
Yes to all the above. Fix what is broken. Its a combination of cable and vacuum. The center **** will be stiffer than the other two, but not stiff enough for you to be breaking *****. If the vacuum wasn't working at all then you wouldn't be able to chose where the air goes let alone the temperature.
Last edited by VIP1; Feb 16, 2021 at 12:37 AM.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
None of mine have ever broken, but if the interior sees a lot of heat/sun then brittleness and fatigue might just be a recurring issue. It should not be super hard to turn any of the *****, though the blend **** does seem to always have more resistance than one might expect (as compared to some other applications).
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Even when I replace the **** it's still stiff to turn slowly compared to the other two *****. I vaguely remember that the HVAC controls are dependent upon vacuum. Could low vacuum, a vacuum leak, or not having my vacuum tank connected (broken line that was capped at the distribution point) be related?
The FSM says to detach the cable from that duct (one bolt) and then test the ****. If it binds or is hard to move, replace the cable. (The FSM implies that it's non-serviceable.)
As you remove the cable from the door, be careful. There is a round housing that engages the shaft for the flapper/door and there is an adjusting spring and other parts in there that you don't want to let loose.
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Verdad Gallardo Thread Starter
Joined: Jan 2002
Posts: 4,072
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From: Casselberry FL
The car has been parked outside practically all of its life, at home in the shade, elsewhere I use a windshield heat screen if I feel its warranted that day. I received a handful of used replacement ***** and a pair of used replacement cables. Regarding vacuum, I have been unable to find an exact replacement for the hose connection between the vacuum check valve and the vacuum tank in over a year. I cobbled something together but I couldn't get it back into the harness that goes over the shock tower so I didn't install it. I'll dig into it this weekend, I appreciate the help fellas.
Teching In
Joined: Feb 2013
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I'm wondering if it's the heat from the bulbs that is causing the plastic to become brittle. I've had to replace the ***** every couple of years. I have an 02 WS6 and it is kept either in the garage or under the carport, granted I do live in Fla. so I don't move the ***** much, they basically stay on A/C most of the time.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
I don't think it's bulb heat specifically because the problem only seems to be a common occurrence for those folks from FL or other very hot places. I don't think anyone up north has reported this as a frequent/recurring problem, even on high mileage cars. So ambient conditions (variable) likely play a bigger role than heat from the bulbs (fixed).
TECH Resident
Joined: Jan 2002
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From: Poway, Ca. where GOD and the sun always shines
I don't think it's bulb heat specifically because the problem only seems to be a common occurrence for those folks from FL or other very hot places. I don't think anyone up north has reported this as a frequent/recurring problem, even on high mileage cars. So ambient conditions (variable) likely play a bigger role than heat from the bulbs (fixed).
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