[bigdawg60]

My a/c unit is not cooling correctly,unit runs all night and cools somewhat,I belie=ve the pressure is low,what should be the readings on low & high side tubing.

[JackT]

It depends on several things. How old is it? Some newer units now use R410 and most of the rest use R-22. The pressures with R-22 depend on return air temperature, outside air temperature and air handler/evaporator design. The low side usually runs 65-70 lbs. and the high side 225 - 250 lbs.

[bigdawg60]

Well I tested the unit low side running about 30-35 lbs high I think is very low,running at 80 lbs A/C unit is about 2-3 months old,high eff,now after I shot some r-22 into it air temp at vent is about 60 degrees, but still notice unit running longer then it should. Also I noticed the high side line is at outdoor temp (Not hot) is this normal on high eff units?

[letmetellu]

If your unit has been running for several hours with the low pressure at 30-35 pounds it is likely that you evap coil is frozen over and you are not getting enough air across the indoor coil to get a good reading or a good exchange of cool air. Let the unit set for several hours.(six) or if you want put the fan switch to the on position and let it run for maybe three hours. Then check the reading again. The temp of the air just above the indoor coil should be 18-20 degrees cooler than the air entering into the return air.

[JackT]

Your small liquid line shouldn't be hot, only on a real hot day. If it is hot you need to clean your condensing unit coil. There's a lot of things to consider when properly charging a unit. Proper superheat is the most important one. Too much refrigerant is just as bad as not enough. Outside temperature will also effect the discharge temperature coming off the evaporator coil.

[Jaime giron]

What about R410 what's the differential pressure.