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  1. #1
    Join Date
    Jan 2007
    Location
    Sparta, NC
    Posts
    85

    Carrier A/C Freezing Up

    Hello, I still in school and working for Burger King Stores, in my store we have about 5 units on the roof. For some reason they freeze up when the A/C is running too long over night if some rooms have heat on and the other side have A/C on. I know the problem kind of, they have them set on auto for both cool & heat mode and the fan as well. I been told the reason is that because of this. They must be set to auto on the heat & code mode, but the fan must be set to on all the time in order to stop from freezeing. I not too sure why this would cause to freeze two units up. But my store manager always get them froze up to where it won't run anymore. Is there some kind of switch that locks out the compressor and fan from running when it freezes up? How can I unfreeze the two units as they won't run and it getting warm in the dining room.

    I would thank for any help.

    Shane

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,302
    Change the filters. Often.

    Clean the blower wheels.

    Clean the evaporator coils.

    Swap out all thermostats with Honewell Vision Pros and lockout the screen after setting temperature setpoints so nobody can change them.

    Once you remove about ten thousand hands from monkeying with the thermostats, along with the other steps listed above, the freeze-up problems should go away...unless the ductwork is crappy and/or the enthalpy controls on the economizers are whacked.

    90% of fast food freeze up problems are thermostat monkey related. The rest is airflow. Get them both under control.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Jan 2007
    Location
    Sparta, NC
    Posts
    85
    Quote Originally Posted by shophound View Post
    Change the filters. Often.

    Clean the blower wheels.

    Clean the evaporator coils.

    Swap out all thermostats with Honewell Vision Pros and lockout the screen after setting temperature setpoints so nobody can change them.

    Once you remove about ten thousand hands from monkeying with the thermostats, along with the other steps listed above, the freeze-up problems should go away...unless the ductwork is crappy and/or the enthalpy controls on the economizers are whacked.

    90% of fast food freeze up problems are thermostat monkey related. The rest is airflow. Get them both under control.
    I just did a PM about a week ago, so everything looks clean, but the blower wheels may need some work. As far as the ducts go, I have not really looked into them just yet and have a feeling they have never been worked on since the store had been open. I have been thinking about switching the thermostats as all the other store has the same ones, but may need to get premission first from the big boss who owns the stores.

  4. #4
    Join Date
    Dec 2006
    Location
    MD
    Posts
    35
    If all the airside stuff is ok,filters,belts,coil. and You think its a t-stat monkying problem You might try installing a remote bulb t-stat in the return air up on the roof.Wire in sereis with Y from t-stat and set for 68* or 70*.This will give You a low limit that only You can change and will shut off comp before it gets cold enough to freeze.

  5. #5
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,491
    You may also need to install fan cycling controls for the condenser fans. Your coils may be getting too cold during cooler weather. You may not be developing enough head pressure.
    Doug

  6. #6
    Join Date
    Mar 2007
    Location
    Vinton, La.
    Posts
    17
    All above suggestions are good, but if it is the t-stat being set real low, install a dial type stat in the return air and break y1 and y2 wires with it. Set it at 70 or whatever. It will override the cooling set point on the stat in the restaraunt no matter what it is set at.

  7. #7
    Join Date
    Mar 2007
    Location
    Dallas
    Posts
    11
    gunslinger has a good point and I would put in the return air t-stat or a freeze stat into the evap. one or the other is fine. After you have proved fan rotation, cleaniness and charge. It should be history after that, however maintainance in fast food places are almost nonexistant

  8. #8
    Join Date
    Aug 2006
    Posts
    442
    Make sure you have low ambient kit, ie (fan cycle, motor master), verify correct blower rotation, belts, filters, etc. Install a freeze stat and a lock box to get rid of sticky fingers

  9. #9
    Join Date
    Mar 2007
    Location
    Austin, Texas
    Posts
    16
    Quote Originally Posted by Gunslinger View Post
    You may also need to install fan cycling controls for the condenser fans. Your coils may be getting too cold during cooler weather. You may not be developing enough head pressure.
    This is a good suggestion, especially since I didn't see mention of OA temp.

  10. #10
    Join Date
    Oct 2004
    Location
    The Zone
    Posts
    392

    One more thing

    I addition to all you have done and are doing I'd add clip on freeze stats to help with dependability and protect the compressor.

  11. #11
    Join Date
    Oct 2006
    Location
    TUCSON, AZ
    Posts
    49

    energy management

    Everyone covered freeze stats, ambient temp controls for the condensers...check out the economizers..if they have them or not see if they are working properly with enthaply. But it sounds to me poor typical low budget energy management controlling, esp if heat running on some and cool on others....there goes there budget right out the fricking window. And they wonder why there profit margin is shot out the window. Had the same problem with a chain store using set back stats with keypad lockouts but they still had heat running with cooling icing up units etc. Then they went to EMS system....pissed off alll the employees and keep nusience service calls from happening, and brought there profits up. Proper monitoring and no more guessing. I am surprised Burger King has not gone to a mointoring energy mgt system of some sort all there competiors are starting to.

  12. #12
    Join Date
    Jan 2007
    Location
    New Hampshire
    Posts
    70

    T/Stat covers

    All the inputs are good but I would start with the cheapest block first. Mount T/Stat guards on all T/Stats and see if this stops your problems before mounting more devices in your ductwork.

  13. #13
    Join Date
    Mar 2007
    Location
    NJ
    Posts
    23

    Talking basics first

    Quote Originally Posted by madcitysw View Post
    Hello, I still in school and working for Burger King Stores, in my store we have about 5 units on the roof. For some reason they freeze up when the A/C is running too long over night if some rooms have heat on and the other side have A/C on. I know the problem kind of, they have them set on auto for both cool & heat mode and the fan as well. I been told the reason is that because of this. They must be set to auto on the heat & code mode, but the fan must be set to on all the time in order to stop from freezeing. I not too sure why this would cause to freeze two units up. But my store manager always get them froze up to where it won't run anymore. Is there some kind of switch that locks out the compressor and fan from running when it freezes up? How can I unfreeze the two units as they won't run and it getting warm in the dining room.

    I would thank for any help.

    Shane
    my first post on here ,, hi to all. the basic things need to be addressed first such as proper airflow, condenser airflow, once3 you have air flow estsblished then you can check refrigeration parameters for system efficiency.no sense in guessing its hands causing your problem until you can eliminate mechanical possibilities first. If your not capable diagnosing a refrigeration or air flow probem i would highly suggest finding a quality firm who can help you out. peace.

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