C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Heater/AC controls-HELP!!

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Old 12-11-2017, 06:26 AM
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Pres712
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Default Heater/AC controls-HELP!!

Has anybody taken apart the '86 manual controls for the heater/AC control unit that is in the dash? The manual shows many vacuum hoses going to various "pots" and some of mine don't work right. I have no heat and the AC is weak. The "flap" for the defroster is in the defrost mode and all the AC goes out that vent. Before I tear this apart, does anyone have any suggestions?
Old 12-11-2017, 09:00 AM
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s carter
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Originally Posted by Pres712
Has anybody taken apart the '86 manual controls for the heater/AC control unit that is in the dash? The manual shows many vacuum hoses going to various "pots" and some of mine don't work right. I have no heat and the AC is weak. The "flap" for the defroster is in the defrost mode and all the AC goes out that vent. Before I tear this apart, does anyone have any suggestions?
Before you start pulling things apart you need to confirm you have Vacuum to the Control because the problem may be under the hood.
So when you move the Vent Selector can you hear a Vacuum hiss as you move from Vent to Vent if so that would show you have Vacuum to the System. Then you could go to some of the vents and see if the request is getting to the vent you are looking at, I have seen the Rotary Valves be clogged but it is Rare.

If you hear a constant Vacuum Hiss you have a leak inside the Dash. If you hear Nothing check for a Broken Vac. tube or Hose under hood. (no supply No vent movement) Your concern that all venting goes to the Defrost That is a Default position it is Thought to see better (defrost/clear windshield) than be 100% comfortable

Last edited by s carter; 12-11-2017 at 09:39 AM.
Old 12-11-2017, 02:32 PM
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Pres712
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Originally Posted by s carter
Before you start pulling things apart you need to confirm you have Vacuum to the Control because the problem may be under the hood.
So when you move the Vent Selector can you hear a Vacuum hiss as you move from Vent to Vent if so that would show you have Vacuum to the System. Then you could go to some of the vents and see if the request is getting to the vent you are looking at, I have seen the Rotary Valves be clogged but it is Rare.

If you hear a constant Vacuum Hiss you have a leak inside the Dash. If you hear Nothing check for a Broken Vac. tube or Hose under hood. (no supply No vent movement) Your concern that all venting goes to the Defrost That is a Default position it is Thought to see better (defrost/clear windshield) than be 100% comfortable
I have vacuum under the hood and a slight hiss when I moved the control from vent to another. Could it be any of the "pots"?
Old 12-11-2017, 03:12 PM
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WVZR-1
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There's a vacuum select switch on the C60 control. There's also I believe a vacuum control for HEAT. The FSM documents operation quite well I believe. Do you have the FSM?

#2 is Vacuum Select and #11 Heat Select

Name:  C60 AC Control.png
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Old 12-11-2017, 03:21 PM
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Originally Posted by Pres712
I have vacuum under the hood and a slight hiss when I moved the control from vent to another. Could it be any of the "pots"?
OK it sounds that you have Supply to the Valve, if you take the Control out leaving the controller in car connected, you can take the Vac. Supply off the Rotary Valve and make yourself a jumper from the Multi hose connector out of a piece of Washer hose and a couple of Hose Splice's. with that in place you can go Port to Port feeling for Vac. in each port of the Rotary valve, you can also go to the different Blend doors and see if you have function of them too.
Old 12-11-2017, 04:40 PM
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Originally Posted by WVZR-1
There's a vacuum select switch on the C60 control. There's also I believe a vacuum control for HEAT. The FSM documents operation quite well I believe. Do you have the FSM?

#2 is Vacuum Select and #11 Heat Select

Attachment 48234217
What is an FSM?
Old 12-11-2017, 05:24 PM
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Originally Posted by Pres712
What is an FSM?
Factory Shop Manual,

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