Been reading the manual again..

[troyport]

Goodman 16 seer 2 stage HP coupled with a modulating furnace and top of the line stat... Goodman wants the charge checked (superheat and supercool) on LOW stage AC.. Manual says nothing about checking charge in heat mode, which from what I understand by lurking and reading on this sight is much more finicky. And why on LOW stage AC and not HIGH stage? Thanks, Mike.

[troyport]

Hello, anyone have thoughts on this? It just seems funny to me to not check charge when running full throttle! Just does not seem logical.

[jtrammel]

I don't know they would want to check it on low, other than to make sure that the 2 stage compressor is operating within parameters on low speed. The only correct way to charge is in air conditioning mode on high speed by superheat(fixed orifice metering device) or subcool(TXV). or weigh in the complete charge.

[beenthere]

Hello, anyone have thoughts on this? It just seems funny to me to not check charge when running full throttle! Just does not seem logical.

Its the way they want, and have apparently proved works best on their units.

[mark beiser]

The first time we put in a Goodmana 2 stage system, I thought the instructions to do the TXV setup, and refrigerant charging, in low speed was a bit odd.
It makes sense though, the majority of the systems operation should be in 1st stage, so why not optimize it for that?
Goodmana is one of the only manufacturers that supplies adjustable TXVs with their equipment.

The only issue I have with it is that, like Lennox, they call for fairly low subcooling values.
Most of our applications have longish refrigerant line sets, and/or >20' of lift, so I have to charge to significantly higher subcooling to avoid capacity loss due to flash gas in the cooling mode.
It isn't an issue most of the time, but they do have some ARI rated indoor coil + heat pump combinations that can't handle the extra refrigerant in the heat mode.