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  1. #1
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,215

    4 wire battery powered thermostats

    New to the industry and I'm surprised how often battery powered 4 wire stats are being used on systems that have 5 wires available. I would have thought 5 wire stats powered through the common terminal would have been standard on a 5 wire system. Most of these are not homeowner installed, some even have company logos printed on them.

  2. #2
    Join Date
    Feb 2012
    Location
    Opelousas La.
    Posts
    90
    Also on some stats that can use batteries or hard wired, when the batteries are installed the time delay function is not used.

  3. #3
    Join Date
    Mar 2012
    Location
    copperas cove
    Posts
    36
    Quote Originally Posted by La Air Man View Post
    Also on some stats that can use batteries or hard wired, when the batteries are installed the time delay function is not used.
    I am pretty sure Time delay will work with a common or with batterys.

  4. #4
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,215
    All the thermostats we install are powered by common wire. Sometimes we have to use an "add a wire" kit to get them to work when there is only 4 thermostat wires. Most times 5 wire cable is pulled but the contractor never hooked up the common and decided to use a battery powered stat instead.

  5. #5
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,337
    The batteries are there to retain time and schedule on stats during power losses.
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    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  6. #6
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,215
    The ones we install require a common wire to operate and a lithium battery for backup. Most of the old ones use the batteries for operation, no common wire connected.

  7. #7
    Join Date
    Dec 2007
    Posts
    4,698
    I see this all to often as well, ALL by pros.

    I always connect them and let the HO know why.

    I just don't get it either.
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  8. #8
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,988
    Quote Originally Posted by La Air Man View Post
    Also on some stats that can use batteries or hard wired, when the batteries are installed the time delay function is not used.
    If your refering to compressor lock, then it's only partially correct.

    If a homeowner cycles the equitment manually, then it would wait the 5 minutes.

    If it attemps to cycle due to a lack of power, then it would not wait the 5 minutes.

    This is due to the thermostat not noticing the lack of power.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  9. #9
    Join Date
    Nov 2007
    Location
    Sherman, TX
    Posts
    9,441
    We get frequent service calls on Honeywell and White-Rodgers digital stats, where the system won't run at all, and the only problem is dead batteries.

    If a 5th wire is there, we use it and hook it to common. If not, then it's batteries. They usually last a good long time....like well over a year.

    A good item to check/replace when doing PMs....
    Technical incompetence is NOT a sales tool....

  10. #10
    Join Date
    Jun 2010
    Location
    Murrieta Ca
    Posts
    30
    umm yea, in case of a power outage, the t-stat dosent go off, that way it keeps its stored memory.

  11. #11
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,337
    ...and yes, hook up the common whenever possible.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  12. #12
    Join Date
    Dec 2007
    Location
    north suburbs of Chicago
    Posts
    520
    Quote Originally Posted by John Markl View Post
    We get frequent service calls on Honeywell and White-Rodgers digital stats, where the system won't run at all, and the only problem is dead batteries.

    If a 5th wire is there, we use it and hook it to common. If not, then it's batteries. They usually last a good long time....like well over a year.

    A good item to check/replace when doing PMs....
    Yep, and you look good for thinking about it as well. I have very few jobs that have extra wires to use anyway.

  13. #13
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,215
    Is 5 wire cable that much more than 4 wire? IMHO when there is only 4 wires it's better to use the fan wire as a common and disable the fan auto/on switch. Hook Y to G at the furnace board and call it good.

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