Low Ambient Charging

[powmat87]

Hey guys im new to the hvac field and have some questions about low ambient charging, here is the situation in which i was in today.

I got a call out to refrigeration walk in cooler it turns out that it was tripped on high perssure from the other day and had a plug condensor, once the condensor cleaned i threw my guages back on and took some sc and sh readings. Here is what i got , 2-3 degree subcool if any, 20 superheat, head pressure was 30 above ambient, a full sight glass and i had a 10 degree split over the evap coil, suction line sweating back nice, 60 degree ambient temp. So where my question is steming from is full sight glass, 30+ ambient head, and 10 degree split over the evap that all looks good. but as far as 2-3 degree subcool and 20 superheat it looks like i could use some gas. So if im without a sight glass to prove the liquid line is full how am i determine wether or not have a good charge?
thanks guys!

[VTP99]

Where is the condenser located and does it have a receiver ?

[powmat87]

The condensor is probably 20' above the case and yes there is a reciever

[VTP99]

So I'll take that as indoors correct ? Is it a pump down system ?

[powmat87]

yep it has a liquid line solenoid which is controlled by the thermostat

[VTP99]

You could pump it down and then torch the receiver to find the liquid level. Don't worry about the sub cooling with refrigeration. Now your super heat looks high to me and should be closer to 10*. Where did and how did you get that reading of 20* ?

[pvc1984]

20 degrees is usually okay at the compressor. In fact copeland requires 20 degrees at the compressor for warranty issues. You should be taking superheat right at the txv bulb and make final superheat adjustments when you get the box down to temperature. Don't worry about sub cooling with a receiver, it doesn't exactly work that way. If the sight glass is clear full, then you have a solid column of liquid feeding the txv, that's the goal.

If the system doesn't have a sight glass, you could pump the system down and braze one in. Then all you have to worry about is evacuating the line set and the evap coil. The job shouldn't take much more than and hour.