Goodman mod

[amd]

How is the GMVM96 controlled?

Does it modulate with a 2-stage t-stat or only with the communicating t-stat?

What kind of algorithm does it use to control output without the communicating stat?

[vibration]

If use single or two stage tstat, just like lennox SLP. If use their CTK2A T-STAT, it's full modulating. I believe the CTK2A is same as Rheem's series communicating modulating tstat.

[BaldLoonie]

With a 2 stage stat, will it modulate to a lower rate if 2nd stage is satisfied or does it stay high like a Lennox?

And with the communicating stat, it modulates based on house needs like a Rheem?

[amd]

I just read the install manual - it works like the lennox.

Low is 50%, not 40% like the others.

Not sure how it works with the communicating t-stat, but I doubt it drops down.

[BaldLoonie]

So even though the stat says less heat is needed, it keeps blasting. So much for long run cycles on gentle, quiet low :( :( :(

[amd]

Perhaps the manufacturers do it to avoid complaints - many people still think furnaces are supposed to cycle a lot.

Manufacturers give the distributors and dealers what they want I suppose; after all, we have 2-stage units which work on timers and the option of using indoor air for combustion.

[amd]

There actually is a mod communicating stat available...

[tedkidd]

Amd, that PDF is very unclear to me. Anybody else make heads or tails of it?

Seems goodman doesn't quite understand the point of modulating OR communicating...

Just tell the system how far away it is and let it try to keep temp tight and match loss! Why do they want it cycling off!?

[amd]

With the mod stat I think it waits until the temp is 2F below the setpoint before ramping up - seems silly to me.

[hvacvegas]

"• If the differential is 2 degrees or less, the Heat Current
Demand Status will show 50%.
• If the specific Heat Requested Demand is above 2 degrees,
the Heat Current Demand Status will track the
specific Heat Requested Demand."

It runs "first stage" if the the desired temp is under 2*.

If above 2*, it modulates, up and down.

Meaning during the middle of winter, without using programming, it will run 50%, and cycle, all the time.

Which, is stupid. Which happens to be why we're not selling it.

[BaldLoonie]

I can't make too much sense of it either. Key is getting the modulating communicating stat if you want the full comfort. But I still can't tell if it will run constantly and ramp up & down as conditions change like Rheem, Trane & Nordyne with their special controls do.

[vibration]

So even though the stat says less heat is needed, it keeps blasting. So much for long run cycles on gentle, quiet low :( :( :(
For 2 stage or their CTK1 tstat, if the second stage calls off and first stage stay on, it will not shift to low fire. I saw the picture of their CTK2 Tstat, It is identical to Rheem's new serial communicating modulating tstat. They said it will be full modulated if you use CTK2 stat.