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  1. #1
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    Goodman GMEC960804CN dip switches.

    Hi,
    I'd like to understand the dip switch configuration tables for my furnace (table on page 36 of the Service manual. Available at manualslib Goodman-Gmec96 page=36

    What does Static 0.1, 0.2...0.8 mean?
    What are the Rise numbers?
    Does the CFM value indicate the max flow for W1 and W2?

    Thanks in advance!

    Seb

    PS. The furnace was professionally installed but an HVAC technician. I just want to understand and monitor the system for maximum savings and see how it compares if I let Google NEST do the math.

  2. #2
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    DROP The desire for the NEST!!!!

    Crap product that does NOTHING for the HVAC equipment.

    As for the numbers, if you don't understand them it is best NOT to mess with them. If it was PROPERLY set up by the installer, or another tech, then leave it alone.

    Those numbers are nothing a typical homeowner needs to understand or can check.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

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  4. #3
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    Nests have a well earned reputation of causing sporadic operation and damage to electronics due to its design. Lots of other tstats let you do what Nest does or better and dont have these issues.
    I dont feel you understanding the manual that came with your furnace is diy, just know that with forced air systems you never just change airflow as it affects everything else, and should be done professionally. The section your referring to shows the effect of rising static pressure on heating operation. As the static pressure increases past 0.5" wc the blower begins to lose cfm and the heat rise between return air and supply air increases. Every furnace is given an approved temp rise by the manufacturer, your is probably from a minimum of 30* to a max of 60* and the manufacturer wants you to run your total external static pressure at 0.5"wc or less. So if you knew your TESP was 0.5" wc and your gas manifold was set correctly then you would be moving 1031 cfm with a 48* temp rise in W1 and 1665 cfm with a 43* temp rise in W2. Outside of these parameters and the system loses capacity, efficiency and can lead to premature wear and tear. Airflow is critical in all forced air systems and this shows really well how excessive static pressure leads to early system failure

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  6. #4
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    I just installed one of these last week. The GMEC series is a nice product overall. There are many techs who never read the manual and never set up the staging or airflow dip switches. It's sad but true. Unless you understand what it means my best advice is leave the switches alone. I second everyone elses concerns about Nest. I've pulled at least 50 of them in the last 3 years because they cause all sorts of problems and even cause control board failures. Any of course that will not be covered under Goodman's warranty, nor should it be........

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  8. #5
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    Oct 2019
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    Thread Starter
    Thanks so much for the helpful response. In fact, I've spend 3 days studying the service guide and I now understand the Airflow tables. I also realize now that the installer did a very odd configuration that is not working well. First off, he has both heat dip switches on. W1 = 1167 CFM and W2 = 933 at 0.5" (this is not recommended by Goodman). Second, he put a jumper from W1 to W2. I'm not sure why. If my current thermostat is setup 1 stage (Nest is missing 6th wire to W2), would you not just connect W1|Nest to W1|furnace and then set the dip switch in S3 so that W2 kicks in after 10, 20 or Auto minutes?

    Thanks for any help. BTW, I've been calling and emailing the installer for 4 days and nothing.

  9. #6
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    I cant even fathom why any manufacturer would give you the option of running the heating fan speed so low it would shut down due to overheating. I would stop calling the contractor bud, they are long gone. You paid for a 2 stage furnace and they made it a single stage, prepare for more such surprises. Get a better contractor to come in a review all deficiencies in the install and suggest fixes. If the installer did crap work when they were being paid, they arent going to come back and do quality work when they are losing money, it just doesnt happen like that, sorry

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  11. #7
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    Thread Starter
    Quote Originally Posted by Makeitcold View Post
    I cant even fathom why any manufacturer would give you the option of running the heating fan speed so low it would shut down due to overheating. I would stop calling the contractor bud, they are long gone. You paid for a 2 stage furnace and they made it a single stage, prepare for more such surprises. Get a better contractor to come in a review all deficiencies in the install and suggest fixes. If the installer did crap work when they were being paid, they arent going to come back and do quality work when they are losing money, it just doesnt happen like that, sorry
    Well, I just removed the W1 to W2 jumper and it makes no sense to bypass Stg 1. Set Stg 1 to 20 min delay, will see how it works, may change it to Auto to compare after 1 month). As for the CFM I changed W1 to 1031 and W2 to 1665 (W2 = W1*62% which seems reasonable to me). It can be worse than what the installer did.

  12. #8
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    Why not just run a new tstat cable with enough wires for a 2 stage tstat to control it, that's the preferred way to control multi-stage equipment. Of course considering the bang up job the installers did, I would guarantee no manual J was done so most likely another oversized equipment on undersized ducting scenario, you might be able to run w1 all winter and never have need for W2. Find out, do a free manual J at Loadcalc.net and see how much heat the home gains and loses over the year

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  14. #9
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    I started running 18/6 yesterday but ran into firewall so it's being tricky but I'll find a way. The house is single-family 1 story 2200 sqft + 2000 sqft finished and insulated basement. Attic is R-60 (just blew some insulation 2 weeks ago). I ran the Manual J and got about 69,813 Total BTU, 980 latent load, 27,400 sensible. The furnace is 80 BTUs (96%AFUE). Trunk duct is 10" x 24" and round runs are roughly 8" in diameter. Thanks for all your pointers!

  15. #10
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    If you cant find a way around to run that wire, Honeywell makes a wireless setup or the communicating Prestige IAQ which only needs 2 wires at the tstat to run most anything. Both have an equipment interface module that has all the wires going from it to the unit and can be placed elsewhere

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  17. #11
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    Thread Starter
    Cool Thanks!!

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