R422D superheat... Can't seem to get my unit to run efficiently

[DTinNC]

Hello and thank you in advance for any help.

I have a split 2 ton system that was originally R22.  The unit was beginning to freeze up presumably due to low refrigerant.  Since R22 is costly I decided to switch to R422D (aka M029 I think) due to availability, etc. 

Captured the old refrigerant (~80% of spec amount so 20% low), evacuated the unit completely for 90 minutes, waited and no loss of vacuum after one hour or so.  Filled with R422D liquid (vapor fill is incorrect) and have been targeting Superheat to determine proper fill.  System is a Fixed orifice EVAP coil.

Dow Company published an R422D chart to use based upon vapor/suction line pressure on gauge.  Chart gives a Dew point temp from the PSI.  The Superheat is then calculated using surface temp of the suction line minus the chart temperature from the pressure on the suction line gauge.

Apparently people say to use the typical R22 superheat chart where Wet bulb temp at return grate intersects the outside temperature near the condenser unit.

Yesterday it was:
83 degrees outside (regular temp)
Wet bulb temp inside near return was 63 degrees

Thus target superheat was somewhere around 10-12ish.

Suction line pressure was 58psi which translates to 34.1 saturated temp
Temp on the surface of suction line about 3" away from service port was about 45 degrees. 

45 - 34.1 = 11.5 degrees of superheat.

Today it's hot again and the line is frozen.

Am I overcharged? Undercharged? Using incorrect numbers etc? 

Sorry for the long writeup but wanted to make sure I provided the details.

Thank you very much!

[Admin]

58 PSI is closer to a 32 F saturation temperature and why you're freezing.  Have you checked to make sure the underside of the indoor coil is clean and indoor airflow is sufficient?

I would check that before I added more refrigerant.

[Sergroum]

Do you by chance have a high velocity system? 

[DTinNC]

58 PSI is closer to a 32 F saturation temperature and why you're freezing.  Have you checked to make sure the underside of the indoor coil is clean and indoor airflow is sufficient?

I would check that before I added more refrigerant.

Thank you.  I cleaned the indoor coil prior to filling.  The tray has some standing water but below the bottom of the coil.  Water does drain through the condensate pipe outside.

The EVAP coil seemed to be smaller than I would have expected.  It's not a typical A coil but instead is a flat coil that is mounted at about 45 degrees.  It's a horizontal unit in the crawlspace with a "hydronic" coil as well.  Could the interior EVAP coil be undersized?  Not sure how to determine since there's no nameplate info. 

[DTinNC]

Do you by chance have a high velocity system? 

Great question. I'm not sure and no nameplate info.  Thank you

[Sergroum]

Your air supply grills.  Are they 4x10 rectangulars, or are they 4 inch circles?

[DTinNC]

Your air supply grills.  Are they 4x10 rectangulars, or are they 4 inch circles?

They are rectangular.  Thank you