Charging a ptac unit?

You need to to determine the superheat and subcooling to check for the proper operation of your system when the compressor is running. I ran into a case just yesterday, the breaker kept tripping. Unit had the same readings as yours. This one had a subcooling of >25 degrees and 0 degrees superheat indicating unit was overcharged. I took an extra 8 pounds of r22 out of the system. During the investigation I also determined the filter/drier was blocking the refrigerant flow causing the technician to overcharge the unit. To check filter/drier performance all you need to do is measure the upstream and downstream temperature. The difference should be less than 2 degrees. This one was 7 degrees indicating it was metering flow. If your compressor stops operating before determining superheat and subcooling, you can get a professional tech to recover and weigh out the refrigerant in your system. You can look on the nameplate data on the side of the outside unit and see the ounces of refrigerant it is charged. If the compressor is operable go ahead and adjust charge by recovering the excess refrigerant into a recovery container for that refrigerant. Normal superheat and subcooling is normally around 10 - 15 degrees.
Hope this helps

Get a high velocity air filter, not a pleated one. Check air into evaporator section clean and passing air well. Next, check proper operation of blower motor and wheel. Next, check for proper charge by performing a superheat and subcool calculation. You will need a repairmant to check these. Superheat and subcool will tell you if your unit is properly charged and if you metering device is working properly. A typical superheat and subcooling value is around 10 to 15 degrees.

Assuming you have the proper equipment to service the unit the best option is to weigh in the charge- superheat/subcooling calculations fly out of the window on mini-splits and the frustration and time spent trying to achieve proper refrigerant balance is more pricy than recovering the charge and reweighing it into the system. If you are not experienced in this field attempting to do so can cause major damage to very expensive equipment.

Hi, sounds as though for this to be its 2nd compressor for such a newer unit, the superheat was not right when the compressor was installed. I don't know what freon you are using the new R-410A or the regular R-22. There's a big difference in pressure, but now I see your pressure reading and its R-22 for these readings.For a 2 ton unit, you would use the superheat charging method for a unit that doesn't use a thermostatic expansion valve ( T X V ) and not the sub-cooling. A 23 degree super heat at that outdoor ambient temperature is way to high for that unit, you will loose the compressor again!!. Super heat killed the compressor is the saying and that's a fact. Suction pressure should pull down just as quick as the head pressure unless the valves are going and weak, or you have a scroll compressor that has a valve plate that is going, or you are low on charge. With a ambient of 95*, you should be at around 270p.s.i. on your head pressure as 210 to 200 is way low. Suction line temp should be around 68 to 70, with a suction line temperature of 50 to 51 degrees, which would give you a 10 to 12 degree F super heat. I don't know when the second compressor was installed, but it has to be low on charge to be such a low head, and high super heat and you will loose this compressor again, its only a matter of time before you have a burnout. It was either under charged when installed, or has a very small leak at one of the joints. I hope the liquid line drier was replaced also. It shows me you have some knowledge on a/c operation, so you need to get that superheat down to between 8 and 10 degrees for this unit to cool properly, and leak check it also. Did you buy a extended compressor warranty? Lets get the head pressure up and superheat down and you should be OK unless the valves or valve plate is weak. Once you loose the valves, you will have a lower than normal head pressure and a high suction pressure. Compressor just won't pull down anymore. I hope I have been of help to you and ask of you to be kind when rating me. I will be here for you if and when you need me for anything.
Sincerely,
Shastalaker7
A/C & Heating Contractor

Charging AC by superheat and subcool
First charging a unit by superheat, this is only for Acs with an orifice or capillary tube.
Optimum superheat is 12° to 15° at the compressor or suction line outside the unit.
Hook up your gages and put a thermometer on suction line (large line), start the AC. Measure the temperature of the suction line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant, (you can also use a temperature pressure chart), now read the thermometer, let’s say the suction temperature( the thermometer) is 67° and the saturation temperature (the gages or temp. press. Chart), is 55°, subtract the saturation temperature from the suction temperature, 67°- 55° = 12° superheat.
Charging by Subcooling, this is for Acs with a thermostatic expansion valve, it’s common to see a sight glass on the liquid line (on these units with a sight glass just clear it, when, indoor room is at approximate set point of the thermostat). Optimum sub cooling is 12° to 15° at the outdoor unit.
Hook up your gages and put a thermometer on liquid line (small line), start the AC. Measure the temperature of the liquid line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant,(you can also use a temperature pressure chart), now read the thermometer, let’s say the liquid temperature( the thermometer) is 100° and the saturation temperature (the gages or temp. press. Chart), is 114°, subtract the liquid temperature from the saturation temperature, 114°- 100° = 14° subcool.

It depends on the indoor and outdoor temperature and humidity. The low side pressure can be in the area of 135# to 145# with an indoor temperature of 80° and 50% relative humidity, and the outdoor pressure can be in the area of 300# to 330# on a 95° day depending on effeciency rating.
If your asking this to charge your a/c this is not how to charge your a/c.
Charging AC by superheat and subcool
First charging a unit by superheat, this is only for Acs with an orifice or capillary tube.
Optimum superheat is 12° to 15° at the compressor or suction line outside the unit.
Hook up your gages and put a thermometer on suction line (large line), start the AC. Measure the temperature of the suction line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant, (you can also use a temperature pressure chart), now read the thermometer, let’s say the suction temperature( the thermometer) is 67° and the saturation temperature (the gages or temp. press. Chart), is 55°, subtract the saturation temperature from the suction temperature, 67°- 55° = 12° superheat.
Charging by Subcooling, this is for Acs with a thermostatic expansion valve, it’s common to see a sight glass on the liquid line (on these units with a sight glass just clear it, when, indoor room is at approximate set point of the thermostat). Optimum sub cooling is 12° to 15° at the outdoor unit.
Hook up your gages and put a thermometer on liquid line (small line), start the AC. Measure the temperature of the liquid line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant,(you can also use a temperature pressure chart), now read the thermometer, let’s say the liquid temperature( the thermometer) is 100° and the saturation temperature (the gages or temp. press. Chart), is 114°, subtract the liquid temperature from the saturation temperature, 114°- 100° = 14° subcool.

You are still low on freon. Charging AC by superheat and subcool
First charging a unit by superheat, this is only for Acs with an orifice or capillary tube.
Optimum superheat is 12° to 15° at the compressor or suction line outside the unit.
Hook up your gages and put a thermometer on suction line (large line), start the AC. Measure the temperature of the suction line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant, (you can also use a temperature pressure chart), now read the thermometer, let’s say the suction temperature( the thermometer) is 67° and the saturation temperature (the gages or temp. press. Chart), is 55°, subtract the saturation temperature from the suction temperature, 67°- 55° = 12° superheat.
Charging by Subcooling, this is for Acs with a thermostatic expansion valve, it’s common to see a sight glass on the liquid line (on these units with a sight glass just clear it, when, indoor room is at approximate set point of the thermostat). Optimum sub cooling is 12° to 15° at the outdoor unit.
Hook up your gages and put a thermometer on liquid line (small line), start the AC. Measure the temperature of the liquid line and read the pressure on your gages. Theres a temperature scale on your gages for R-22 or R-410A the needle will show you the pressure on the outer scale and if you follow it down to the R-22 or R-410a inner scale that is the saturation temperature for that refrigerant,(you can also use a temperature pressure chart), now read the thermometer, let’s say the liquid temperature( the thermometer) is 100° and the saturation temperature (the gages or temp. press. Chart), is 114°, subtract the liquid temperature from the saturation temperature, 114°- 100° = 14° subcool.

try cleaning a-coil

Either or, they both are the same ends but different routes..