Defroster control not working

Midnight LJR

Midnight LJR

In search of Rubicon flares.
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So I have done a bunch of work under the dash the last few weeks so it’s possible I messed something up. Or could just be a coincidence.

The defroster control switch (Not sure of actual name) is no longer functioning. It is stuck on defrost and no air comes out of The main vents regardless of setting.

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Anyone have experience trouble shooting this?
 
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Check your vacuum line from the intake manifold to the tee by the evaporator lines and from the tee to the reservoir under the battery.
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Daryl said:
Check your vacuum line from the intake manifold to the tee by the evaporator lines and from the tee to the reservoir under the battery.
View attachment 169095
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Thank you, I also just found this video that says the same thing. I have been focusing my attention under the dash.


I’ll go check those over.
 
I had the same issue. Vacuum line came off the manifold nipple. Check under the hood, could be a simple fix. Mine was a rotten rubber elbow. #3 on the diagram above. If not the issue trace the vacuum line and look for issues. Its rarely the controls that fail.
 
Also, check the vacuum line behind the glove box where it connects to the HVAC box. The glove box storage box can often pinch the vacuum line shut.
 
Midnight LJR said:
Thank you, I also just found this video that says the same thing. I have been focusing my attention under the dash.


I’ll go check those over.
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You’re on the right path. The HVAC system defaults to defrost for safety purposes when the blend doors loose vacuum.
 
Hmmm doesn’t appear to be a leak in any of those areas. The engine bay lines and rubber all appear to be in excellent shape.

The ones behind the glove box move freely and slide back and fourth. Also tried with the glove box taken out.

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It’s possible I damaged one under the dash during the stereo install but if one is there must be very tiny because I cannot see it.

Are new switches still sold? It might be worth replacing that just to check before tearing really far into the dash.
 
Do you hear a hiss when you turn the dial with the engine off? Does it work properly with the engine running? If there is a leak under the dash you should hear a hiss with the engine running. You can also pull one of the hoses off under the hood that go from the AC section to the passenger fender where the accumulator is and see if it hisses with the engine off. That switch isn't cheap, at a minimum check for vacuum pulling lines with the engine off and on under the hood first to see if that part is working.
 
Have a Mighty Vac or similar tool? Test the line, could be blocked, cracked connector, bad check valve. You can also use it to test the switching controls. Pull vacuum on the HVAC controls and see if they work or not. Process of elimination once you check the easy stuff.
 
pagrey said:
Do you hear a hiss when you turn the dial with the engine off? Does it work properly with the engine running? If there is a leak under the dash you should hear a hiss with the engine running. You can also pull one of the hoses off under the hood that go from the AC section to the passenger fender where the accumulator is and see if it hisses with the engine off. That switch isn't cheap, at a minimum check for vacuum pulling lines with the engine off and on under the hood first to see if that part is working.
Click to expand...

I’ll go try this now.
 
AMS417 said:
Have a Mighty Vac or similar tool? Test the line, could be blocked, cracked connector, bad check valve. You can also use it to test the switching controls. Pull vacuum on the HVAC controls and see if they work or not. Process of elimination once you check the easy stuff.
Click to expand...

I don’t have one. I could go get one.

So this?
https://www.harborfreight.com/mityv...RQh4s6IoxaAFwbgeX309JXViAX6kXwvQaAmUDEALw_wcB
So with this I could just check line by line to see if which one is leaking?
 
Ok just checked Everything in order for Vacuum all the way up to the switch.

I have good vacuum at the mainline to the switch, but can hear leaking as soon as I turn it on. So looks like a bad switch.

Thanks for helping me troubleshoot. Looks like next step will be a new switch.
 
Midnight LJR said:
Ok just checked Everything in order for Vacuum all the way up to the switch.

I have good vacuum at the mainline to the switch, but can hear leaking as soon as I turn it on. So looks like a bad switch.

Thanks for helping me troubleshoot. Looks like next step will be a new switch.
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Before you order, make sure none of the vacuum actuators are leaking or the lines to them, especially the one just to the right of the accelerator pedal.
 
Daryl said:
Before you order, make sure none of the vacuum actuators are leaking or the lines to them, especially the one just to the right of the accelerator pedal.
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Yeah apparently for the 05-06 that thing $550 that’s not fun. 04 and earlier is only $140.

Would the actuators cause a leak at the switch? Do those go into the HVAC box with all the flappers?
 
Midnight LJR said:
Yeah apparently for the 05-06 that thing $550 that’s not fun. 04 and earlier is only $140.

Would the actuators cause a leak at the switch? Do those go into the HVAC box with all the flappers?
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If the diaphragm in the actuator is leaking or a vacuum line has come loose you’ll hear the air moving through the switch.
 
Daryl said:
If the diaphragm in the actuator is leaking or a vacuum line has come loose you’ll hear the air moving through the switch.
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This right? I don’t see anything obvious wrong with it.
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Thanks again for all the help everyone and yeah I will look used $550 is crazy.
 
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