Results 1 to 9 of 9
  1. #1

    Weird issue with Lennox A/C + Honeywell t-stat, please help!

    Hi guys,

    The warm season has started and I went out few days ago to start up my Lennox A/C (XC16), and it doesn't work, something really strange happens.

    I have a Honeywell visionpro iaq thermostat.

    My furnance is also a Lennox G61MPV90.

    When I switch the system setting to cool and wait for the 5min delay, what happens is the thermostat shuts off, blank screen and my furnace (if set to FAN ON) shuts off as well. Then the unit resets and started the 5 min delay again.

    These are the things I've isolated so far to test what's wrong, to my knowledge. I'm a QA software engineer, so I can only approach things to this degree.

    1. Swap thermostats, same thing happens to another honeywell t-stat I own.
    2. Check A/C breaker and outside pull switch is passing current. No problem there
    3. Check any shorts in the Y1 Y2 or C wire to the A/C unit or from t-stat to furnace PCB. Nothing, tested with multimeter.

    I tried searching and the only other thing I could find was something about the condensate safety switch triggering the shutoff. But when I run the heat cycle, it runs fine, unless there's a condensate switch for the condenser? I don't see any wires coming out or going anywhere from the drain and there's nothing but a pvc elbow coming out of the condenser.

    The only switch is the one for the furnace and that seems fine, otherwise the heat won't work?

    Is there some sort of safety switch or breaker on the A/C unit somewhere that would trigger shutting down my t-stat? If there is, how is that possible when only 3 wires go from the furnace to the A/C unit (Y1 Y2 C)

    I guess I can measure the voltage across those terminals and see what is going on but I'm really confused why it's behaving like this.

    Oh, and my A/C Unit is about 1 year old, the furnace is about 1.5 years old.

    Any suggestions?

  2. #2
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,582
    There is a short somewhere on the control circuit that occurs when the call for cooling is made. The voltage drops due to the short causing the thermostat to reset (which is fortunate as it is preventing damage to a fuse or transformer). You might check to see if the dog has chewed the wires going out to the condensing unit, but either way you will need a service call.

  3. #3
    Quote Originally Posted by cjpwalker View Post
    There is a short somewhere on the control circuit that occurs when the call for cooling is made. The voltage drops due to the short causing the thermostat to reset (which is fortunate as it is preventing damage to a fuse or transformer). You might check to see if the dog has chewed the wires going out to the condensing unit, but either way you will need a service call.
    thanks, which control circuit would it be? the one in furnace or ac?

    the short would be between what though? y1 and ground?

  4. #4
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,582
    I can't get very technical on this site, but you are on the right track. The condensing unit, furnace, and EIM (white "honeywell" box near the furnace) are all tied together. I don't recommend putting your hands into any of these as damage to equipment or yourself could occur. There could be other issues as well with a circuit board or other component, but this kind of thing usually turns out to be wiring.

  5. #5
    Why can't you get technical?

    Well it should be something in the condensing unit since I haven't touched anything in the house since I tested the A/C

  6. #6
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,582
    Quote Originally Posted by FlashEngineer View Post
    Why can't you get technical?

    Well it should be something in the condensing unit since I haven't touched anything in the house since I tested the A/C
    This site has rules, and mods watch closely:

    http://hvac-talk.com/vbb/showthread....NO-DIY-Why-NOT

    Like I said, it could be anywhere, without having seen the system myself I still think you are on the right track.

  7. #7
    Join Date
    May 2009
    Location
    Cummins, GA
    Posts
    1,547
    Call a pro.

    You have a low voltage short. This is not a DIY scenario. Sometimes issues like this can throw off even the most seasoned professional.

  8. #8
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    549
    Did you by chance install a new thermostat yourself at some point?

  9. #9
    Join Date
    Aug 2012
    Posts
    2,720
    ENGINEER run for the hills.
    My name is TooCoolforschool and I am a chronic over charger.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event