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Thread: Honeywell and low voltage R to G causing stat to keep system running

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    Honeywell and low voltage R to G causing stat to keep system running

    This all started with a call to Honeywell for what I thought was a defective Tstat less than a year old. In fact the complete HVAC system was replaced less than a year ago, but let me start from the beginning. I notice intermittently the system kept cooling and it got very cold. I would go the the Tstat and turn it up but within 30 seconds the command temp I set it to would match the room temp displayed. After a few days of this I called Honeywell sure it was the stat. The kicker was when I turn the command temp down to get it to turn on and within 30 seconds the actual room temp displayed matched the command temp without the AC ever turning on. So, They had me test the voltage from R to G, R to W and R to Y at the Tstat wiring on the wall. R to W&Y were 27.5 volts but R to G was low only 15.7. Honeywell said I need to get that fixed first. Call the HVAC guys $**** later they said it was a bad connection at the harness connector running to the blower fan(inside unit) all fixed. No...the system kept doing the same thing. So, I called Honeywell back thinking the voltage issue had been fixed. To my surprise I had the same readings R to G was low 15.7 volts. (Note this is with no command to the system, the Tstat is unplugged. So Back come the HVAC repair guys. About 30 minutes later it's the module on the blower. A few days later (today) they come back with the blower and module assemble and replace them. Two hours later and the system has not shut off my cheap hand held thermostat reads 75, and the TStat says it's 78 actual and command temp is set at 78. turned system to off waited 2 minutes removed Tstat tested R to G reads 15.7 volts??? Being a retired auto technician we many times had issues with poor grounds. I think that's the issue, but where. Tech info - System model # EBE15A . Tstat is an RTH6360 with the setup command to not use programing. In other wards the system should only command to set or hold temperature. One other clue. With the wiring to the Tstat removed and testing at the unit R to G still reads 15.7 and the others read 27.5 including the C wire that does not run to the Tstat, but if you also unhook the control wires running to the outside unit from Y and C the voltage on R to Y will drop to 15.7 . When Y is hooked up to the outside unit the voltage is correct at 27.5 ??? Seems to me it's finding a better path to complete the circuit ??? That wire to Y from outside runs to the contactor then the circuit leads back the the transformer common on the wiring diagram. The blower fan also has a low voltage common wire running to the transformer, the circuit diagram shows them both running to the same connector on the transformer. Any Ideas where the issues is?

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    Last edited by rundawg; 08-08-2022 at 04:43 PM. Reason: removed pricing

  2. #2
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    When you say the system is running, do you mean the air conditioner or just the fan.

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    The outside unit is running as well as the inside, so when the Tstat fails to turn the system off it starts getting cold.

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    You're measuring voltage incorrectly. It also appears your technicians are not very skilled.
    Look for a better technician.

    Site rules do not permit giving technical advice for DIY. Note the sentence in red at the top of the page.
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    I am not sure what honeywell is getting at with their voltage test. I kinda get it but yet not. With the test they had you do the common side of the transformer was coming back through the coil in a relay. The G circuit may not have a coil in the circuit as it has been replaced by a board and module in many cases.

    Over the years there have been many compatibility issues that have been solved with a pilot relay. I would have your tech try that to see if that solves the problem, or change to a different thermostat to see if the problem goes away. Nest would probably not be a good alternative in this case.

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    I'm just following the direction from Honeywell while on the phone to try to get them to warranty the Tstat. They said with stat removed to but the red prob + from the volt meter to R at the wall where the stat plugs in. Then put the neg prob from the meter to G the reading is 15.7 ac. While leaving the red on R check the other 3 wires W & Y. the voltage reads 27.5. Their conclusion is R to G must be the same as the others or 20 to 30 volts. What ever the output of the transformer is.

    FYI - I'm not a DIYer just stuck between HVAC repairs and Honeywell looking for direction to go next or possibility to relay to the HVAC folks even if I get a new set of eyes on it. I also called Coleman the Manufacturer and their tech department said the same thing as Honeywell there is a issue with the system if the voltage is low R to G. I also know that the stat wiring was eliminated by unhooking all the stat wires at the unit then testing R to G at the unit and the voltage is still low. R to all the other wires it 27.5 except if you remove the low voltage wires to the outside unit too. Then G and Y both have low voltage.

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    Thanks, I'm going to go purchase another tstat today. It's frustrating because all of this stuff is less than a year old and I'm going to be out of pocket well I guess I can't say...many many many. Thanks for the info about compatibility and a Pilot relay. No idea what that is, but I will relay that to the Tech.

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    Does the fan only setting actually work?
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.
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    Quote Originally Posted by bgpianoman View Post
    I'm just following the direction from Honeywell while on the phone to try to get them to warranty the Tstat. They said with stat removed to but the red prob + from the volt meter to R at the wall where the stat plugs in. Then put the neg prob from the meter to G the reading is 15.7 ac. While leaving the red on R check the other 3 wires W & Y. the voltage reads 27.5. Their conclusion is R to G must be the same as the others or 20 to 30 volts. What ever the output of the transformer is.

    FYI - I'm not a DIYer just stuck between HVAC repairs and Honeywell looking for direction to go next or possibility to relay to the HVAC folks even if I get a new set of eyes on it. I also called Coleman the Manufacturer and their tech department said the same thing as Honeywell there is a issue with the system if the voltage is low R to G. I also know that the stat wiring was eliminated by unhooking all the stat wires at the unit then testing R to G at the unit and the voltage is still low. R to all the other wires it 27.5 except if you remove the low voltage wires to the outside unit too. Then G and Y both have low voltage.
    By definition, you are Doing It Yourself. It does not matter that Honeywell tech support told you to do it.
    The problem could be diagnosed by a competent technician.
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    And that is what Honeywell expects the home owner to do if you can test the voltage at the stat. All the other info was done by a certified HVAC company and recheck by them as part of their diagnosis. I have not touched the HVAC system...again just asking a question. Who is right ! Honeywell and Coleman both say there is an issue with the system if R to G voltage is low. Now that the repairs are done by the certified HVAC company they are saying the voltage is not an issue and replace the Tstat. I don't want to know so I can go work on it. The reason is the system is under warranty and I want to know it's totally fixed. By the way UPDATE; The Tstat was replaced yesterday and now turning the system on and off correctly for the last 12 plus hours. Even though I still want to know if the R to G voltage being low is still an issue that might be a failure waiting to happen. Or possibly damage the new Tstat.

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    Thats not how you test it.

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    I tried to reply but it didn't go through. So when they test the voltage from R to G and R to W or R to Y it's not a valid test? In the post missing I stated that the stat was replaced, but failed in less than 24 hours. Same exact issue.

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    See post 4 and 11. That’s what we told you.
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    So Honeywell and Coleman are wrong when they say lower voltage on R to G ( 13 to 16 volts) is a problem when R to W & Y is 27.5 volts. Then what should it be?

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    Quote Originally Posted by bgpianoman View Post
    So Honeywell and Coleman are wrong when they say lower voltage on R to G ( 13 to 16 volts) is a problem when R to W & Y is 27.5 volts. Then what should it be?
    Depends. Not something ive really tested, because it proves nothing.


    Its like ohming out a gas valve.
    Its not a valid test of anything.

    Or in car terms, its like asking what the correct temperture a EGR valve should be.


    As far as tech support, people i call, in this order:
    Buddy of mine.
    Service manager.
    Sales rep.
    My mom.
    Manufacturer.

    Ive also never called a manufacturer for warranty approval.

    You buyinf home depot honeywell stats?

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  21. #16
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    That would all depend on what is on the other end. A circuit board will be different than a relay, which may be different than another component.

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    OK The EGR analogy works...when combined with it depends what you are hooked up to. Knowing that many sensor in automotive systems have feedback loops to control a devices operation. The EGR valve gets a command to open and close, but in some cases other input like a temperature sensor changes that command. If this blower fan module has some type of variable resistance on the G circuit the readings they are getting make sense. Also would explain why the Y circuit is reading normal voltage until the control wire running to the outside unit is removed and then the voltage drops. It's circuit path back to common is then only through the blower module. I knew that was a clue. What you are showing me is this blower is not simply on or off. The module has some kind of input that must make the speed vary.

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    If you hire an experienced technician they would know what tests have meaning and could have resolved this already. Most likely without replacing the thermostat.
    Climate Control Solutions for your Home or Office

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    Quote Originally Posted by bgpianoman View Post
    So Honeywell and Coleman are wrong when they say lower voltage on R to G ( 13 to 16 volts) is a problem when R to W & Y is 27.5 volts. Then what should it be?
    Yes they are wrong,
    Honeywell was probably running you through some basic testing procedure that they found works on certain systems but evidently not yours.
    I doubt any HVAC technician would use anything like that procedure because there are too many variables that make it useless.
    You probably have an ECM or X13 blower motor where there is no fan relay to read the common feeding back on the "G" terminal.
    The resistance would be different on the motor than a typical relay coil so they would have no idea what the voltage should read on "G".
    I'm still unclear about what your actual problem is. When you talk about turning the Tstat up or down, are you talking about a degree or two or much more than that?
    The simplest way to test the system is to turn the Tstat up or down like 10 degrees either way so you know it should definitely turn on or off given whatever the delay period might be.
    If everything goes on & off like it should then most likely the problem is the Tstat & no voltage tests are needed.
    Either way all this should be covered by the installation company for the first year unless you installed the Tstat yourself.
    Gary
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    http://www.oceanhvac.com
    The best things in life are free but not everyone is willing to pay the price.

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    Thanks Gary and all that have spent time helping. Now I know what to tell the pros (???) that come to fix it.

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