80L48

I know there are allot of similar posts, and I have read allot of them, but cannot find this circumstance:

Before I order some parts, I wanted to get some guidance on what is happening in my car. I recently purchased it so I don' have all the history.

My problem is: The air only blows out of the heat duct when the switch is in AC Norm, Vent, Htr, or Defrost. In AC Max, it does come through the vents partially.

I have the Schematic and will refer to that in my description (Thanks Willcox!)

I have removed the actual plastic vacuum switch from the HVAC console, but the lines can still be connected.

I can get the following to occur while the car is running and fan speed set to high:

• I am getting vacuum through the black line to the switch. (port 1)

• Bypassing the vacuum switch and using a vacuum pump, I can pull a vacuum (simulating a connection to port 1) on the individual Blue, Tan, and Green lines
  • Blue Port 3 - when vacuum is applied (simulated with pump) Air diverts to Defrost vents
    
  • Tan Port 4 - when vacuum is applied (simulated) with pump Air diverts to upper and side vents
    
  • Green Port 5 - activates Outside air/Recirc air valve actuator
    
• If I connect all back to the switch, and simulate the positions that would occur if it were mounted in the head unit - Nothing happens.
• However, if I continue to rotate the lever beyond where it would stop at the Defrost position (the lever is now upside down!) I can get vacuum to flow through and activate the various airflows. It is almost as if I needed to mount the switch upside down! , but with the guide holes and alignment with the Head Lever, this cannot be done.
  
• So, the switch appears to be capable of holding vacuum, but cannot route the airflow properly to the ports
  
• Could the internal routing of vacuum from port 1 to the other 3 be somehow internally reversed? I have not opened it up yet.
  

Appreciate any guidance or feedback anyone may have.

• Are the colored lines activating the right airflows?
• Any thoughts on the switch?
  

0Willcox Corvette

I can't see your picture but I'll assume it's this chart you have. In most cases issues with the HVAC can be attributed to the vacuum select switch. If you move the switch and it doesn't function as prescribed below then I'd replace that switch.

You can take the switches apart at the rivet and apply some grease inside and the install the rivet. This will in most cases fix a leaking vacuum select switch. If not, we have them.

0Willcox Corvette

Here is a thread that will help you too.

https://www.corvetteforum.com/forums...on-switch.html

80L48

It was the switch, took it apart, put a nylon bolt through center and Dielectric grease. All good now.