Vacuum leak on ac controls

Discussion in 'Interior Restoration' started by mrluckies, Oct 30, 2020.

  1. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    I have a 1970 camaro with factory ac. While installing the ac system in the car, I decided to test for leaks by connecting a vacuum pump to the ac vacuum line that goes to the engine. When I did this, I have a small vacuum leak. So I took the control switch assembly out of the dash and pulled the hoses off of the distribution valves (the rotary pieces that are moved when you move the function and temperature levers on the control panel). I tested each port and all of the hoses and vacuum actuators are fine, no leaks. I then tried vacuum testing the rotary distribution valves themselves (there are two, one for function (off, ac, vent, heat) and one for temperature (cold, hot)). These are what the vacuum lines connect to on the ac control panel in the dash. When I connect the vacuum pump to one of the ports and plug all of the other ports, I get a slow vacuum leak. It’s leaking between the two halves of the rotary distribution valves. These are just metal halves with a spring loaded center pivot. So I don’t see how a new one would be any better. Does this seem normal?
     
  2. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    Here’s one of the rotary distribution valves I took off of the ac control panel. It leaks between the two halves.

    60AD8429-092D-4B8C-B799-BB2C4626BAD5.jpeg F6E75211-EAD1-4766-9295-2E4936CAAF75.jpeg 7298715B-96DA-4A02-8B2A-522C27EFB838.jpeg
     
  3. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    Here’s some pics of the distribution valve on the ac control.

    2A5FAF3F-5BB0-4D6D-9810-BD829FB7FB3D.jpeg 00BA80DF-0C51-4756-AE51-A0DE180AF1A4.jpeg AD2C70EA-74AD-4605-9425-D73BC53867B5.jpeg
     
  4. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    I'm not much help here as I've never pulled this part of the HVAC control system apart to test for leaks.

    If it's a small leak and the vacuum actuators still move through their full range of travel, it may not be a problem.
    There's always vacuum present to that control head when the engine is running so a small leak could be normal.
    I'm not sure how the two halves actually seal against each other or if there is a good, long term fix, if it is a problem.
     
  5. mrluckies

    mrluckies Veteran Member Lifetime Gold Member

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    Thx for the reply. I agree that I don’t know how else it would seal. It seems like a small leak is always possible. There’s no o-ring or gasket on there. Just two metal surfaces sliding on each other.

    my main concern is if the small vacuum leak will cause issues with the engine tune. I guess it’s no different than the pcv as long as it’s a consistent small leak.
     

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