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  1. #1
    Join Date
    Dec 2003
    Posts
    148

    White Rodgers T-Stat

    I have a system w/ a 1f95-1277 that the zone temp is 5+ degrees lower than acctual temp. I replaced this stat a couple weeks ago for the same problem (seemed fine at the time). Now, with the stat on the subbase and the old stat on a table, the old stat reads correctly and the new stat incorrectly. I am wondering if the issue is related to a floating xfmr. I called tech support and he told me to remove the common wire, I asked if this was due to a floating xfmr and he sounded confused.

    I don't do a whole lot of resi, but I do a lot of controls and floating xfmrs always seem to cause problems. I think because in the circuitry they refernce ground thru the common.

    I am just curious if anyone has had this experience w/ these stats.

    The furnace is a Goodman, again, not being familiar w/ resi furnaces I'm not sure if they use floating xfmrs. I am not on the job, my tinner buddy is there as the job is far away from me. I will not be able to go for a week or so to fruther check, just looking for some input.

    Thanks for any help!
    Still learning....

  2. #2
    Join Date
    Jun 2012
    Location
    Rising Sun, Maryland, United States
    Posts
    110
    Is the tstat in a central location? Any supply or return near it?

  3. #3
    Join Date
    Jun 2003
    Location
    French Settlement, Louisiana, United States
    Posts
    286
    What part of the country are you in? Are the t-stat wires coming thru the wall from an attic? I have seen large holes drilled for wire torun down wall that allowed heat into back if stat.

  4. #4
    Join Date
    Feb 2013
    Location
    Sonora, California, United States
    Posts
    1,029
    Quote Originally Posted by coolcajun View Post
    What part of the country are you in? Are the t-stat wires coming thru the wall from an attic? I have seen large holes drilled for wire torun down wall that allowed heat into back if stat.
    mine is in a hallway with a shower on the other side of it and often comes on due to the hot showers and probably humidity.

  5. #5
    Join Date
    Dec 2003
    Posts
    148
    The stat is installed on a colum in a custom cabinet that seperates the family room and kitchen, no supply or return within 10 or 15 feet. The hole in the colum was filled with rubatex.

    I think this is purely a wiring issue due to the fact w/r tech support told us to remove the common wire.

  6. #6
    Join Date
    Dec 2003
    Posts
    148
    Time to revisit this... The stat has been working correctly all summer using battery power. Now, that things are cooling off I need to get this fixed to use the OAT sensor to control the hybrid heating system. I attempted to call W/R to discuss but the tech I spoke with had no clue and told me "Joseph" would call me back. Needless to say, no phone call back and no answer after 15 min on hold. I am going to recheck all the wiring on this job tomorrow. I guess if I cannot find anything wrong I'll have to change out the stat to a Honeywell. I need this job to end, any ideas?

    I can definitely say I am done with W/R. The poor tech support has been frustrating. I think the product is good, but they need to stand behind it and help when it doesn't work.
    Still learning....

  7. #7
    Join Date
    Sep 2009
    Location
    Hampton, GA
    Posts
    572
    agross, what do you mean by floating xfmr? Honeywell is a good bet. But that is odd for W/R, they make good thermostats overall. Usually most advance thermostats like that have a option to - / + in calibrating the thermostats actual temperature.... have you tried to calibrate it?
    wHen I diE I hOpe gOd haS mErcy oN my SiNful LifE

  8. #8
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,834
    I gave up on White Rodgers a few years ago because tech support could not resolve problems with two thermostats in my own house. Their products were not reliable.
    I've had very few problems with Honeywell products and tech support has been good.

  9. #9
    Join Date
    Dec 2003
    Posts
    148
    Quote Originally Posted by mofotech View Post
    agross, what do you mean by floating xfmr? Honeywell is a good bet. But that is odd for W/R, they make good thermostats overall. Usually most advance thermostats like that have a option to - / + in calibrating the thermostats actual temperature.... have you tried to calibrate it?
    A floating xfmr is one that the common or neutral leg is not tied/bonded to ground. When not bonded to ground the potential difference to ground on any leg will float with a different amount of load. ie. 10VAC to ground on one leg and 14VAC on the other to ground on the other to equal 24VAC. This typically does not cause issue, however when dealing w/ electronic circuitry that references ground can cause malfunction. I know for a fact that Sporlan EXV drivers require a floating xfmr, as do some Honeywell actuators (I'm not sure why, maybe they are grounded internally or maybe it provides noise on the input control signal).
    This is no different than the 240/120V transformer feeding your home. The neutral leg is bonded to ground to prevent the voltage on either hot leg from floating.

    Additionally, I did a little bench testing w/ a 1f95-1277 today. I found that the remote sensor is returning a frequency signal back to the tstat to transmit temperature. I am beginning to believe that on this particular job EMI is causing my problem. I am going to go back and change the location of the remote sensor and run shielded wire (currently have just 18ga. tstat wire).
    Still learning....

  10. #10
    Join Date
    Dec 2003
    Posts
    148
    Quote Originally Posted by kdean1 View Post
    I gave up on White Rodgers a few years ago because tech support could not resolve problems with two thermostats in my own house. Their products were not reliable.
    I've had very few problems with Honeywell products and tech support has been good.
    Tech support was terrible. Guy I talked to told me to reset to factory defaults at first. What good will that do?
    Still learning....

  11. #11
    Join Date
    Sep 2009
    Location
    Hampton, GA
    Posts
    572
    Quote Originally Posted by agross View Post
    A floating xfmr is one that the common or neutral leg is not tied/bonded to ground. When not bonded to ground the potential difference to ground on any leg will float with a different amount of load. ie. 10VAC to ground on one leg and 14VAC on the other to ground on the other to equal 24VAC. This typically does not cause issue, however when dealing w/ electronic circuitry that references ground can cause malfunction. I know for a fact that Sporlan EXV drivers require a floating xfmr, as do some Honeywell actuators (I'm not sure why, maybe they are grounded internally or maybe it provides noise on the input control signal).
    This is no different than the 240/120V transformer feeding your home. The neutral leg is bonded to ground to prevent the voltage on either hot leg from floating.

    Additionally, I did a little bench testing w/ a 1f95-1277 today. I found that the remote sensor is returning a frequency signal back to the tstat to transmit temperature. I am beginning to believe that on this particular job EMI is causing my problem. I am going to go back and change the location of the remote sensor and run shielded wire (currently have just 18ga. tstat wire).

    Thanks for the explanation! Doesn't the common on the transformer usually be tied to ground in most air handlers or furnaces? I am just asking to learn. (I am kinda fresh out of school ) Ya try the shielded wire and also check the settings for the remote sensor option. I looked over the install manual of this thermostat, it kinda looks like you can only have one sensor installed and used. ( either indoor or outdoor) Or maybe I am wrong?
    wHen I diE I hOpe gOd haS mErcy oN my SiNful LifE

  12. #12
    Join Date
    Aug 2010
    Posts
    2,921
    How does the OAT wiring get to the thermostat? The sensor circuitry works in the mV range and if you're sharing wires in the same jacket as the 24v AC wires, the induced capacitance can cause interference and cause incorrect readings.

    How long is the OAT wiring? Normally you'd want to use twisted pair shielded when you're dealing with a long analog wiring and bond the shield to a common point.

    When the common is not connected, thermostat circuitry lives on the coil side of the island with its own battery power.

    Crappy power supply design is entirely possible. My postage scale works perfectly fine on its 9v battery. As soon as I connect an external power through the adapter port, the capacitive coupling immediately cause it to malfunction, which is due to poor isolation between the load cell op-amp and external power port. Designing things for external power requires much more thorough interference rejection consideration. El-cheapo battery only thermostats are completely isolated on its own island, because nothing on the circuit ever come together with the 24v control wires.

  13. #13
    Join Date
    Dec 2003
    Posts
    148
    mofotech, you are right this stat can only have one remote sensor, we are using OAT due to a hybrid heating set up.

    ICanHas, my plan at this point is to pull sheilded wire as a home run from the sensor. The installers used stat wire w/ a splice in the furnace and it does have 24VAC in with the sensor wires. I would have thought W/R would have used a more robust signal, maybe a 4-20, to prevent interference.
    Still learning....

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