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Discussion Starter #1
Did a search first but didn't find anything. I have an '87 with the V8. The control panel is stuck on the defrost and floor positions, doesn't matter where I move the position to, vent, defrost, A/C, it doesn't blow through the front vents, only the defrost & floor. Even the A/C blows cold in this stuck position. I pulled the panel out & can't find anything obvious broken or missing in the dash. What am I missing, what's going on? Thanks!
 

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Controls work off engine vacuum. Check the small grey vacuum line connected to the intake just behind carb. Follow it over and down the fender well for breaks. They get brittle and break.
 

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Actually it should be a purple line that feeds into the control head from the manifold. The gray line that 464elky is referring to actually should go to the heater control valve to shut water off to the heater core when not needed. Actually on my 86 it is a black vacuum line coming from the manifold and has a factory connector along about the fan relay on the ac box under the hood where it then changes to the purple vacuum line. With that being said like he mentioned check both for cracks or breaks that could lead to the vacuum leaking and in return not controlling the ac / heat doors as it should. Also you have a 9 port or so vacuum switch on the control head that could be leaking. I replaced mine because I could hear the vacuum leaking when I put it in certain positions. If it leaks there may not be enough vacuum to pull the doors into the position required to direct the air flow where desired. There is also a 2 port vacuum switch on the control head.
 

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I thought about that after I had walked away from the pc - but then I thought he will check them both. SORRY about that.
NAPA can order the repair for the vacuum switch. Not home to get you the number.
 

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Where did you find a replacement? I posted several different part numbers and vendors for them here many years ago, just cannot find that post.

Thanks
 

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Everco # 36694. I got them thru NAPA a couple of years ago. Have 2 spares
 

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wtg Tom
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usually you can pop the top off and replace the o-rings and grease them real well,
and your good to go, sometimes you need to tighten up the clamp on the 2 halves...
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Four Seasons 36694 Vacuum Mode Selector Switch:
ACDelco 15-71389 Part Number(s): 1571389, 15-71389, AC1571389
GM Original Equipment Climate Control Vacuum Valve
MT0803 Santech A/C Selector Mode Switch
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https://frugalmechanic.com/auto-part/4-seasons-36694-switch
https://frugalmechanic.com/auto-part/ac-delco-1571389-heater-valve
https://frugalmechanic.com/auto-part/santech-industries-inc-mt0803-switch
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:texas:
 

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Reviving a dead thread, anyone know where I can find one of these now? Can't seem to find one anymore.
 

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Most of those sites have them out of stock. Assuming they even have them in stock though for that mount of money I'll probably try my luck rebuilding the one I have now first. Really appreciate the info.
 
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