Superheat and Subcool on 410A

jgronczniak

I have a 40 ton AAON rooftop unit with copeland scroll compressors running on 410a refrigerant. I was wondering what my SH and SC should be. I have 132 psi suction and 350 psi discharge and am getting a 26 deg superheat and a 61 deg subcool. It has a TXV. My outdoor temp is 80 deg and return air temp of 72. I dont really have much experience with 410 and not sure what kind of numbers i should be getting. Thanks for any help.

Vaporx

I have no experience with 40 ton equipment, but superheat and subcooling values are generally consistent regardless of the type refrigerant. Which would suggest 26 is high for the superheat and 61 is way high for the subcooling.

The suction pressure and SST is normal, but 350 could be high for the head depending on the unit SEER. Residential 13 SEER equipment would be closer to 300 for an 80 degree ambient. It's about right for 10 SEER.

Are you using the right P-T chart for saturated temperatures?

Vaporx

Something else to consider...to have 61 F subcooling with that head pressure, the liquid line would have to be 45 F or so. That sound right?

jgronczniak

I am using the temp reading on my guages. They are set up for 410 refrig. I am getting a 45 deg sat. temp on the low side and reading 76-77 on the line itself at the compressor.

Vaporx

Well, that eliminates errors in saturated temps. But I still can't fathom a 60 degree subcooling value. I once saw a resi heat pump in the heat cycle with 50 F subcooling, which way the hey overcharged...

artco

What are you getting for discharge air (supply)temperature?
Does the compressor have unloaders?