86 C20 - Climate control not changing position - cable or vacuum operated?

[kapitein]

Hi,

I know this is a well traveled road, in fact there is so much info, sometimes its difficult to pick out what you need.

After spending $1000s I have beatiful ice-cold AC in my 86 C20 Burb. However, all that air is going straight to the floor. When selecting the different modes on the dash control the AC compressor will switch on/off correctly according to the position, but the rod that actuates the big door behind the glovebox doesnt move.

I can move it freely by hand, and the door(s) open and close correctly without interfering with each other.

Is that rod assembly actuated by vacuum, or is it cable operated (and therefore im missing a cable...) All my vacuum lines appear to be connected, but I cant 100% say its all correct as someone has been messing around in the last 40years and who knows what they did.

Anyone who has been through this before, would love some advice on how to get the mode select working again.

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[fast 99]

85 has a vacuum supply. However most vehicles will default to defrost if vacuum is lost.

 

[Snoots]

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It may be that one of the vacuum pots has gone bad because you said the rod moved easily. I hope this diagram helps.

 

[YakkoWarner]

Also make sure the vacuum is connected in the engine compartment. My 1989 has similar issue (although the A/C doesn't do much anymore) with the routing doors. Turned out the vacuum line ging through the firewall was broken, so none of the diaphrams that move the doors did anything. The heat blend door still worked because it is cable operated.

 

[kapitein]

So far Ive found some fun stuff.

The vacuum supply from the engine bay, well that was holes up directly to the cruise control diagphram

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So that's now temporary connected to permanent vacuum on the carb (bypassing the vacuum pot)

This improved things slightly in the interior.... But I still can't get those doors to move (and therefore no air from the middle vents).

I found this hanging behind the dash... Does anyone recognise it?

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[Broken85]

That is the vacuum line that is most definetly not connected to the vacuum pot it is supposed to and likely your trouble. If it was behind the dash it is probably the bi level pot. I hope you are flexible!

 

[Snoots]

So far Ive found some fun stuff.

The vacuum supply from the engine bay, well that was holes up directly to the cruise control diagphram

You must be registered for see images attach

So that's now temporary connected to permanent vacuum on the carb (bypassing the vacuum pot)

This improved things slightly in the interior.... But I still can't get those doors to move (and therefore no air from the middle vents).

I found this hanging behind the dash... Does anyone recognise it?

You must be registered for see images attach

You found your problem!

 

[Grit dog]

Yup. That goes to one of the vac ports on the hvac box. If you take off the glove box door and remove the glove box most of them are pretty easily accessible.
Removing and reinstalling the whole thing under the dash is one of those cuss for 2-3 hours the first time and much easier when repeated.