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  1. #1
    Join Date
    Dec 2005
    Posts
    7
    I'm working with a dual fuel setup: Lennox HP with a gas furnace to run as the auxilary. Originally, there was a standard hp+aux thermostat (with the furnace set so it would only run if the user switched the tstat to "emergency"... this prevents the hp and furnace running simultaneously.

    To improve efficiency, a dual-fuel tstat was installed, but since then, the hp will not run at all, even when the original tstat was reinstalled... but rather, when the compressor (Y) lead is engaged, the furnace turns on only. (Of course, this occurs when the aux (W) lead is engaged).

    what would cause this?

    thank you to anyone to can help!

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,396
    What kind of stat is being used now? Is the old DF kit out of the works?

  3. #3
    Join Date
    Dec 2005
    Posts
    7

    tstats

    The original stat is a MapleChase dual-stage heat pump (though the system has the wiring for a single stage w/aux). The HP was wired as expected while the aux was empty... the furnace was wired to the emergency-heat terminal. This ensured the hp and furnace wouldn't run at the same time.

    The new stat is a Carrier TSTATCCPRHO1-B with the outdoor sensor and dual-fuel capability. I configured it for dual-fuel and wired it as would be expected (Y=compressor, W/W1=furnace...). Everything checked out except that when the "heat" is on, the furnace runs and no hp. I pulled off the furnace wire and same thing...

    so, as it stands, the hp will not run with either thermostat, and the furnace is turned on with either the yellow or black wire.

    as to the DF kit, I really don't know. I didn't remove anything but the old stat, and I only added the temp sensor.

    [Edited by jeffdg on 12-01-2005 at 01:47 PM]

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,396
    Either something not configured right on the stat or something in the low voltage not right. We use the Vision Pro as our dual fuel kits. They work great and are simple.

    Lennox used to have some crazy designations for what their low voltage terminals do, makes it a challenge for us normal people to wire.

  5. #5
    Join Date
    Dec 2005
    Posts
    7
    Assume (for the moment) that it (the t-stat) is wired correctly (esp. since the old stat *now* does the same thing):

    What could cause the compressor lead to activate the furnace? Local breaker/fuse to the compressor?

  6. #6
    Join Date
    Dec 2005
    Posts
    7

    UPDATE!

    Okay, new info:

    I reinstalled the Carrier t-stat and selected test mode (overrides all the programming to allow individual testing of HP-heat HP-cool and aux/e-heat (the last one is the furnace).

    aux/e-heat works as expected: furnace turns on...

    the HP-heat is quite odd: it turns on the HP for about 1-2 minutes and then switches the furnace on (aux heat) (it should stay on hp for the entire test run of ~4 minutes). I don't know why it would do this. Suggestions?

  7. #7
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    You really need a tech to come out and and wire the system correctly.
    Karst means cave. So, I search for caves.

  8. #8
    Join Date
    Mar 2005
    Posts
    66
    Out of curiosity, what is the outdoor temperature when all this strange stuff is going on? Then also what is the balance point setting at? Could it possibly be that the outdoor temp is below the balance point only giving you the heat pump for a short time?

  9. #9
    Join Date
    Dec 2005
    Posts
    7
    good questions:

    temp was 36 according to the OD sensor.
    Balance point set to 30

    But... I was in the "test mode" which (I believe) overrides all these settings and simply cycles the HP for four minutes under "heat", and furnace four minutes under "E-heat"

    oddly, under the "heat" is when it cycled for two minutes with the HP and two minutes with the furnace. I could hear the relay 'click' in the tstat when it switched over.

    Anyone who knows the Carrier Thermidistat, I have the wiring diagram shown in Figure 11, and mine is hooked up exactly like that, except I do not have a humidifier. I have 8 wires:
    yellow: compressor
    black: furnace
    green: fan
    orange: changeover valve
    blue: common
    red: hot
    tan: t-sensor
    white: t-sensor

    [Edited by jeffdg on 12-02-2005 at 10:16 AM]

  10. #10
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    If you are not in the business then call someone who is, if you are a tech then post this in the Pro section. I was going to tell you how to jumper it to bring on the heatpump but don't care to get my pecker smacked. Post in Pro and I will put up the wires to jumper to test the heatpump. Rules state no DIY in here, don't want to give out any info that will burn out any parts.
    "Go big or Go Home"

  11. #11
    Join Date
    Dec 2005
    Posts
    7
    The hp is fine, works fine with the old stat, I just couldn't wire the furnace as the auxilary since it wasn't a dual fuel t-stat.

    When I first hook up the new stat, it acts as before during test: 2min hp, 2 min furnace. But, after awhile, it will only run the furnace and not the hp at all, even thought the wiring is identical. Defective stat? Have carrier expert coming next week.

  12. #12


    Please give us some info of whether you're in the field. If so, we will be glad to help you further...

    But if you are a DIY, please see the link below...

    Thanks for your understanding.

    (we can't help DIY due to site rules )

  13. #13
    Join Date
    Dec 2005
    Posts
    7
    I am a professional engineer, but not a Carrier expert.

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