Filtrete 3m50 'C wire' hookup on GMPN100-4 Question

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Old 01-04-11, 12:24 PM
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Filtrete 3m50 'C wire' hookup on GMPN100-4 Question

I have a Goodman GMPN100-4 REV B, and am attempting to hookup a new 3m Filtrete Thermostat with WIFI from Home Depot. It takes batteries but it also requires a 'c wire' hookup for the WIFI to operate. I have removed the stock Honeywell 4 wire thermostat with R, Y, W, G hookups. There are unused wires that run from the thermostat to the furnace that I can use for the 'c wire' connection. It is my understanding that the 'c wire' hookup is for 24v power.

My question is: Where do I hook up for the 'c wire' connection on the circuit board ? Within the furnace I have an open place labeled '24V HUM', which is unused. There is also some sort of transfomer with multiple wires connected labeled 24 on the lower and 120 on the upper with multiple red, blue, and white wires leading out. Can I attach to either one or am I totally wrong?

Any help would be appreciated and I will respond to any questions, if any.

Thanks,
 
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Old 01-04-11, 05:11 PM
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follow the 24 labeled wires out of the transformer. what colors are they?
 
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Old 01-04-11, 06:55 PM
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http://www.hvacpartsshop.com/Gmph075-4%20Series.Pdf

Refer to page 64.
24 volt common is the transformer's thinner blue wire that is also connected to the furnace chasis.

You can connect your common wire to the furnace chasis.
 
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Old 01-04-11, 07:36 PM
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coming out of the transformer is:
upper left labeled COM is a white wire going to the circuit board labeled PRI TRNS
upper right labeled 120V is a black wire going to the circuit board labeled PRI TRNS
lower right labeled 24V is a red wire going to the circuit board (plugged in with a group of wires/not really labeled)
lower left labeled 24V is three blue wires-one going to what appears to be ground, one going to the circuit board (plugged in with a group of wires/not really labeled), and one going out of the furnace with a massive gob of wires/not sure where leading

all of the wires a the same thickness, about 1/8th inch
 
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Old 01-04-11, 07:43 PM
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connect to the blue wire or the furnace ground
 
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Old 01-05-11, 07:24 PM
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Thanks guys for all your help. The 'C' is Common and I connected it to one of the Blue wires coming out of the 24vac side of the transformer which also goes to the furnace chasis.

Just started using this thermostat and I LOVE IT. I can control the thermostat from my iphone anywhere.

Thanks again.
 
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Old 06-20-11, 10:31 AM
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Goodman GMP075-3 & Serious Noob

I have a similar setup, my Goodman does not have a C on the circuitboard and I'm trying to setup a 3m-50. Here's what I have:
  • Blue wire at the tstat that was not previously used
  • Two blue wires (one light blue) at the furnace connected to the 24v connector on the transformer
  • One or both blue wires appear to connect to the chassis also

I tried connecting the blue wire to the tstat but it did not power it up. My questions are:
  • When landrover333 said, "The 'C' is Common and I connected it to one of the Blue wires coming out of the 24vac side of the transformer which also goes to the furnace chassis," how do you do that? There aren't anymore connectors on the transformer.
  • What exactly did he connect, the wire coming from the tstat? I thought my tstat blue wire was one of the blue ones already connected at the furnace, but from my pics it looks like the furnace ones may be bigger than the tstat wires so maybe they're different (not in front of furnace) this is where I get confused.

Total newbie to furnace wiring here so sorry for what may seem like obvious questions. I have pics if that will help.
 
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Old 06-20-11, 10:05 PM
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cut and spliced the wire in................
 
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