Questions Regarding HP Sizing And More

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Originally Posted by LibertyTree

I'm in the pacific northwest near the coast so we don't get warm summers here. I have always sized for loss here, am I doing things incorrectly? The customer has never really used the air conditioning feature. He said maybe two or three times so its hard to get a good idea of how it works in cooling. What kind of bearing does the duct have on the output in this case?

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If your in a no A/C needed area. Then sizing for the heat load is ok. Duct work if its large enough for the 3 tons, or even large enough or 4 tons has little bearing on temp delta across the coil as long as the blower is set up for the right CFM for the heat pump size.

A 2 stage/multi stage heat pump just slows the indoor blower when the heat pump is running in first stage. So with a 4 ton 2 stage heat pump. When its in first stage you basically have a 3 ton running on a 4 ton duct system. And still have a good temp rise.

Get the air flow correct, and then find out why it has a poor temp delta. Could easily be that it was over charged if they had the blower speed/CFM set too high.

Assuming R22 system 216psi head=>107F- 72F LLT= 35F subcooling. Overcharged?

The ductwork should not be a problem. As long as it's not too small, it will not adversely affect performance of the equipment.
You said you weighed in the charge, so I don't think it could be overcharged enough to perform that poorly. A 15 deg temp rise assuming nominal 1200 cfm is less than 20,000 btu. I would look for a possible restriction or problem with the TXV in the outdoor unit. The suction pressure would help. I'm guessing it's low.
I'm interested in what you find.