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  1. #1

    Heat staging and controller

    OK my first question for the site....But first, I do control systems for petrochemical industry, plants, so I do have some control experience 37 years worth. I'm in south east Texas, it's been cold here lately. First year where I needed any real heating in the house, just moved into it. Small home 1900 square ft. But I noticed my heater cycling a lot and the house staying warm but it seem the heater ran to much and the heat coming through the vents was not warm. So I had to take a look.

    Pretty much a standard thermostat for heat (heat strips not a heat pump) and A/C control. One heater output control "R" and "W"...

    Fan Control board in the unit is a Texas Instruments HQ1085914TX....Unit has either the 7.5KW or the 10KW strips by the wiring diagram, I cant see the numbers to know exactly which. But it has two individual heat elements, AMFK07 or AMFK10, one of the two and I suspect the AMFK10 as the breaker was sized at 60Amps.

    Looking at the typical wiring diagram for this unit, they show W1 and W2 on the Fan control as jumpered. Mine wasn't. This morning I jumpered it and when the heat came on, we got the typical burn off heat, set off the smoke detectors. The heater has been on for several weeks now, so obvioulsy only one of the elements has ever been powered up.

    I removed the jumper I do understand fan speeds and heat removal. My controller is for a single fan speed, speed relay is not present. The fan itself is a three speed fan currently hard wired for a single speed, medium.

    So my question to you folks, is this normal? I could understand if the Fan Controller actually did the staging, but it looks to me as if this was wired wrong from day one. I'll have my A/C guy out tomorrow, but could some one have choosen a single fan speed controller and then decided to only use one element for heat because of fan speed?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,176
    Usually 10 kw is w1. Additional 5 or 10 kw increments are w2.

    Sent from my HTC VLE_U using Tapatalk 2

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    Its a normal set up.
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  4. #4
    Name:  Schematic.jpg
Views: 251
Size:  21.6 KBThis unit shows two independent 5Kw strips controlled by two seperate relays and each relay having it's own control wire feeding it. There was a definate difference in the heat from the vents with the W2 jumpered.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,176
    I stand corrected. Haven't seen that on a 10kw before.

  6. #6
    I would get the odd ball OK I beleive they didn't understand the Fan Control board and heat staging on the unit when they installed it. But for safety sake, I'm going to put a thermometer in the duct work and check my heat rise and watch it for a few days....it's chilly in this house.....

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,176
    Yea, 1/2 your heat on could lead to a chilly house. If I were wiring it, I probably would have ass-u-me d typical and just used W1 on a 10kw kit.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,085
    Probably what the installers did.

    Should haven't any heat rise problem, since you said it was barely warm with only 5KW.
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  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,289
    1900sqft heated with 5KW all those years. House must either be insulated really well or it normally just doesn't get cold where you live.

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