Subcooling on home AC

[low temp]

Hello, I am a novice at air conditiong & need some help. Last winter I had a contactor install a larger (4 TR) coil & put in a TXV on my air conditioning system when he changed my furnace out to a high efficiency unit. My condensing unit is a 3 TR York 10 SEER on R-22 that is about 5 years old. My question is what subcooling should I be seing out of it so I can check the charge. I can't find this information anywhere as it appears TXV's are only used on higher SEER systems. If you need data we can assume 85'F ambient, 70# suction and 75'F indoors with about 230# head.

The contractor I used did not know what he was doing and I dont believe his charged the system correctly as he put the sensing bulb for the TXV inside the coils cabinet & attached it with Nylon ties. I corrected this when it got hot and my suction SH dropped from 30'F to 15'F at the compressor and my suction pressure increased about 5 psi. The unit is cooling much better now as you can imagine.

Thanks

[Entropie]

The subcooling is designed for the pressure drop in the refrigerant liquid line to avoid flash gas bubbles in the liquid line fed to the expansion valve. 10°F (5K) is a good value with compressor fully loaded and condenser and cooler fan on full speed. It is important that you measure the liquid refrigerant pressure and temperature at the same point.

[Brian_UK]

If the TXV is working correctly then the charge is correct.