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  1. #1
    Join Date
    Aug 2012
    Location
    Monticello, IL
    Posts
    27

    Display of VAV CFM erratic and now 0

    We have Delta's DVC-V304A controllers on our VAV boxes. On one of the units the CFM is erratic and is not reading correctly (typically reads lower than actual.). After speaking with Delta and them checking out the programming they said the issue was the controller. We replaced the controller and still have the same issue. Anyone have any ideas? Could some of the holes in the air sensor be clogged?

    Thanks

  2. #2
    Join Date
    Feb 2007
    Location
    Helena, Montana
    Posts
    2,155
    I'm not familiar with that specific model, but have seen tubes get holes in them over time. I would check all of the tubing. I would think the sensor would get clogged if filters are changed regularly, but stranger things have happened.
    Don't worry zombies are looking for brains, you're safe...

  3. #3
    Join Date
    Aug 2012
    Location
    Monticello, IL
    Posts
    27
    Thank you will check that. There doesn't seem to be an easy way to get into the sensor to check that section of the tubing.

  4. #4
    Join Date
    Apr 2011
    Location
    Chicagoland Area
    Posts
    37
    It's usually the tubing, not the sensor. Most of the time people will install a "T" and put a rubber plug over the "T" port, these tend to dry rot and crack. If your lines are good, then check the sensor itself by connecting main air to each (the hi and low), this will hopefully blow out any debris that may have clogged it.

  5. #5
    Join Date
    Aug 2012
    Location
    Monticello, IL
    Posts
    27
    Thanks for the input. I began paying closer attention to rest of the VAV boxes in that building and noticed several that are erratic. About half are on one AHU and the other half on another. The building is only 10 years old.
    Also, it is not a pneumatic system. Could we use canned air to try and blow out the sensors or, if not, bring in a small compressor?

  6. #6
    Join Date
    Apr 2011
    Location
    Chicagoland Area
    Posts
    37
    Absolutely, you can use whatever air you want. You wouldn't want to use too high of an air pressure (20-25 psi should be sufficient).

  7. #7
    Join Date
    May 2009
    Location
    in the present
    Posts
    91
    If you don't have enough straight duct up stream, you can have too much turbulence at the sensor and see this type of issue.

  8. #8
    Join Date
    Aug 2012
    Location
    Monticello, IL
    Posts
    27
    Quote Originally Posted by kirkH View Post
    If you don't have enough straight duct up stream, you can have too much turbulence at the sensor and see this type of issue.
    Thanks. I have been suspicious of that. This box is about 2' after a 90°.

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