Goodman GMVC95 Only Working On One Fan Speed? Temperature Incorrect? New To Me Home - HVAC - Page 2 - DIY Chatroom Home Improvement Forum
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Old 10-14-2015, 12:27 PM   #16
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Yeah but we are not living in the Disco era anymore. Most people under 35-40 yrs old were born with electronic devices, Nintendo, cell phones and are comfortable with programming anything.

On your mercury tstat its accuracy new was +/- 2 deg F and is more now with age. Any electronic tstat is accurate to 1 deg F. Yours gives you nice LONG swings and cycles which old people like.
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Old 10-14-2015, 12:41 PM   #17
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Funny thing about the electronic stats; people promote them because they don't have mercury. Yet the chemicals required to produce the semi-conductors are pretty toxic. The electronic stats often use batteries which have to be thrown away.

The exotic materials in electronics can't be recovered easily.

Wheres the mercury is just a liquid in a sealed tube, it can easily be removed and recycled. The issue is getting people to recycle them.

Electronic devices, while great in some ways, are an environmental disaster.

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Old 10-14-2015, 02:02 PM   #18
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Ok guys, home from work, figured I would give a good run down of what Im seeing and a few pictures for reference.





What Im working with in the crawlspace



And with the circuit panel cover removed





I also located the cable run to the thermostat from the furnace, pretty shotty, no grommet, the wall the thermostat is on is "in general" right above this area, but you never know whats in the way in a 100 year old house I suppose



Im going to see if anything in the manual is understandable by a laymen like myself, Im curious what the numbers in the sight glass mean, it shows c0 currently with the furnace not doing anything

Thanks so much again for the help guys
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Old 10-14-2015, 02:19 PM   #19
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So your thermostat is currently only wired to the control board for 1-stage (W1) heat.
Dipswitch #3 on bank SW1 needs to be set to "off" for a 1-stage thermostat, but the factory default is "on"....I would check that first and foremost.

It's not a problem using a 1-stage thermostat with this 2-stage furnace, by setting the dip properly the furnace logic will use a runtime history algorithm to stage itself. Alternately, you could run a wire from W2 on the thermostat to W2 on the control board, in which case the thermostat logic would take over staging decisions.

"c0" is a communications error...not sure why you are getting that, as your control board is not being used in a comm mode, with a Goodman OEM comm thermostat. If it was, you would have wires on a different green wiring plug (4 positions only) connected to "1" and "2" (the data lines) on the control board and R and C.

I would power off completely and check that thermostat selection dip, then restart and see what you get. Display "OP" is normal standby mode, waiting for a demand call from the thermostat.
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Old 10-14-2015, 02:20 PM   #20
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Hard to see from your pictures of the control board, but is there a row of little dip switches that can be turned on and off on the board? Some furnaces allowed you to run as a single stage unit (high speed only), or a 2 stage unit by adjusting the dip switch setting.
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Old 10-14-2015, 02:24 PM   #21
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When it's running it tells you what's happening, stage, cfm.

Switch the heat on and tell us what is displays; the display should cycle between the mode and and numbers once the blower is on. After 12 minutes if it doesn't switch to high, it's set up wrong

Getting it to run on high fire will just make things worse.

Post the full furnace model number, size of the house, construction, age, and trunk duct sizes. That could give us an idea as to if it's oversized.
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Old 10-14-2015, 03:14 PM   #22
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Quote:
Originally Posted by KevinEF7 View Post
Ok guys, home from work, figured I would give a good run down of what Im seeing and a few pictures for reference.
Yeah... I sort of figured... a bad home hack job thermostat install. Not enough wires in the wall to support 2 stages at the thermostat.

You can run another wire or you can do as mentioned above and set the furnace up for staging on the furnace board.
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Old 10-14-2015, 03:33 PM   #23
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Originally Posted by WyrTwister View Post
That someone was me . Was not rocket science . And I only had to set the heat anticipatory . No other programming involved .

Single stage cool , by the way .

God bless
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5 minutes to set up a digital thermostat, including a set back program if desired.

So you didn't check temp rise across the heat exchanger in both stages, and adjust the blower.
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Old 10-14-2015, 03:46 PM   #24
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Originally Posted by WyrTwister View Post
Electronic tstats !

My 2 stage heat condensing furnace is connected to a 2 stage mercury bulb stat . Worked properly from day one .

KISS - Keep It Simple Stupid

Most home owners could not program a VCR , back when we had VCR's . And someone installs an electronic stat with more options than the VCR . :-(

God bless
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The advantages of a digital stat FAR outweigh the older ones. The drastically increased detail in the control means money in the pocket.

As for programming... pretty easy now. With interview based programming on the higher end ones it's almost impossible to go wrong.
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Old 10-14-2015, 04:35 PM   #25
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Sorry guys I was reading the unit wrong, it wasnt displaying c0, since the unit is mounted horizontally you have to read it sideways, was actually reading 0n.

I did find the dipswitches after a few minutes of searching, there so tiny I passed over them multiple times before noticing they were switches, as Done That stated though, #3 on SW1 was indeed switched on, I switched it off and thats all I touched, first picture is before dipswitches, second picture after. Anyone see anything else out of spec?





Also Im curious, if running it only as a single stage, does it only run on high? If thats the case I would like to definitely install the proper wire to run it to its full potential, if the setting it runs on currently is high, I would be much happier with a quieter low speed

A little more info was asked on the model, house etc.

Model # GMVC950704CXAC
House is approx 800 sq feet not including finished loft (bit there are no vents there). The house was built in 1900, has a field stone foundation, just a 10X10 crawlspace for a "basement"
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Old 10-14-2015, 05:22 PM   #26
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It should start at a low speed, then ramp if demand is not met. Will ramp down when demand is met, to pull any residual heat off of the exchanger after flame is off. Last ramp should only run for aprox. 30 sec's then furnace will shut down.

Is that sheet metal that the wire running through the Cold air return?



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Old 10-14-2015, 05:57 PM   #27
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Yes that sheetmetal duct remains cold while the furnace is blowing heat, I spent a good while and a full roll of aluminum tape just now closing up all of the air losses on the seams and such, trying to make my first home as efficient as I can.

Really do appreciate the help guys, I enjoy DIY so much more than calling a repair man and not being involved
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Old 10-14-2015, 06:20 PM   #28
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Quote:
Model # GMVC950704CXAC
House is approx 800 sq feet not including finished loft (bit there are no vents there). The house was built in 1900, has a field stone foundation, just a 10X10 crawlspace for a "basement"
Leave high fire disabled. With a single stage stat and the dip switches set for a two stage thermostat, it will run on low only. High fire will make the noise problem worse.

For 800 sq ft even with no insulation and excessive leakage, the furnace is very grossly oversized. The finished loft if heated by another source actually reduces the heat loss.

Low fire alone should probably meet the needs of the house; if you want high fire for fast warmups, you have to connect W2 so it only comes on when needed. You do not want this furnace running on high.

Actually being familiar with the gmv, the 70k model moves 900 cfm from the factory on low fire while your ducts may only be sized for 600 or so in that space.

It's obvious that this furnace wasn't comissioned properly, so I recommend:

1. Clocking the gas meter to see if the fuel input is correct. If it's not, you'll have to call someone to check and adjust the gas pressure.

2. Looking into cutting the fan speed down. These furnaces ship from the factory with the heating fan speed set fairly high, and you can reduce it by 10% or so. You just have to check the temperature difference between the supply and return after doing this; exceeding the range spec'ed by the manufacturer can shorten the life of the furnace.

This is not as much of an issue with the type of furnace you have (the fan motor automatically compensates for the air ducts, to a great extent), but with really undersized ducts, it's a concern.

Post back for more info.
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Old 10-14-2015, 06:23 PM   #29
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Quote:
Originally Posted by KevinEF7 View Post
Also Im curious, if running it only as a single stage, does it only run on high? If thats the case I would like to definitely install the proper wire to run it to its full potential, if the setting it runs on currently is high, I would be much happier with a quieter low speed
Unlike most multi stage thermostats that are time/temperature based, the board is time based only. It will start in low and ramp up after a certain time period.
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Old 10-14-2015, 06:33 PM   #30
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Quote:
Originally Posted by KevinEF7 View Post
Yes that sheetmetal duct remains cold while the furnace is blowing heat, I spent a good while and a full roll of aluminum tape just now closing up all of the air losses on the seams and such, trying to make my first home as efficient as I can.

Really do appreciate the help guys, I enjoy DIY so much more than calling a repair man and not being involved
If your crawlspace is ventilated and uninsulated, either the ducts need to be insulated or better yet, the crawl space needs to be converted into the equivalent of a mini-basement with vapour barrier on the floor, proper insulation on the walls.

uninsulated ducts in a cold space really drive up utility bills.
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