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  1. #1
    Join Date
    Nov 2007
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    Vision PRO IAQ /w fuelmaster 21


    I recently moved into a 2 story 2700 sq/ft house /w a lennox signature 3.5 ton A/C - heat-pump system and older Trane xe60 furnace /w Aprilaire 760 humidifier. It has a fuelmaster 21 connected to it as well.

    I purchased a Robertshaw 9725i2 thermostat /w outdoor sensor but I don't like it. I don't the fact I can set a compressor lockout (balance) temp but then get limited to 40 minutes of stage 1 heat because of the upstage timer. Very frustrating when it's about 45-50 degrees outside and the sun is out during the day my house warms up from heat-gain; then the temps drop quickly at night. The furnace will be off for hours during the day and when the thermostat kicks on it will need more than 40 minutes to stabilize the temps my home. Consequently I'm back on AUX heat after 40 minutes when the heat-pump could have stabilized it in another 10-15 minutes anyway...

    I've had enough with the 9725i2. I also wasn't too impressed with Invensys's tech support. I called and talked to someone there in tech support and explained my problem with the heat gain and he basically just told me "it's binary; under the balance the compressor is off, over it's on... and no you cannot shutoff or over-ride the upstage timer" .. ugh (live and learn)

    So.... I hung-up and I ordered a Visionpro IAQ /w an outdoor temp sensor on-line. After doing some reading on here I realized it has a lot more control!

    Anyway... what I wanted to know.

    Should I/Do I need keep the fuelmaster 21 when I setup the Visionpro IAQ? My fuelmaster does not have the defrost module/probe.

    Couple of other questions I had...

    What stops the system from shutting off the heatpump during the defrost if the t-stat calls for AUX heat or the temps have satisfied? (My thought was the fuelmaster... I noticed it has a deforst detect line that runs back from the HP, and the light illuminates when defrost is activated)

    What stops the furnace from running at the sametime as the HP? I know the robertshaw stat had an options to choose wether to allow it or not. I had it setup to not allow AUX and HP to run simultaneously. Was that correct?

    Also whats the standard number of cycles per hour you want on a heat-pump? Or how do I go about determining that number?

    Thanks in advance for any answers! So much to learn...
    Last edited by Irix; 11-30-2007 at 05:32 PM.

  2. #2
    Join Date
    Nov 2007
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    I don't think my questions are in the DIY realm; just general function with the fuelmaster 21 and heat-pumps in general. If so let me know and I'll bug off.

    Otherwise no-one is familiar with the equipment and or configuration I'm talking about?

    I found some threads on compressor cycles per hour for heat-pumps but it didn't get technical as to why they should be set to cycle X amount of times. Just some people suggesting 3 cycles per hour. I'd like to know why...

  3. #3
    Join Date
    Nov 2007
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    HVAC guy was out today for yearly maintenance. He took the time and answered all of my questions. Even brought out the IAQ install manual of his own...

    Fuelmaster 21 isn't needed with the IAQ stat.

    IAQ stat will control if the HP and AUX run at the same time. The only time it's acceptable to do this is during defrost...

    Compressor cycles per hour; I found a few good threads if you search... Lots of opinions and HVAC guys input... conversations about 80% furnaces and 5 cycles vs 90%+ furnaces and 3 cycles...

    Anyway, hopefully this info helps someone else out if they are getting their stats upgraded to be sure it's installed correctly.

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