I have a trane air conditioner operating at 70psi low side pressure but with little to no temperature on liquid line by condenser but is cold to the touch entering the air handler

You need good airflow across the indoor coil, the evaporator. Air warms the refrigerant. If there is no airflow, the refrigerant will come back out freezing cold (in liquid form) and can damage the compressor valves. Before charging any ac unit, good airflow must be checked for across both evaporator and condensor.
Too much, overcharging will cause freezing all the way back to the compressor in a capilary tube type of ac.
Where is it the refrigeration lines are freezing cold?

i would suspect the valve on suction side not open. if the other system failed on a burn out you could have a blocked dryer or orfice at coil.

150 is low for high side pressure. may have to add more r-22 to system. if you had a blockage high side pressure should be higher. have you turned both service valves at condensor ccw completely?

That piston is the metering device. On the liquid line, before the metering device it is always warm (this is sub cooled, high pressure liquid), but should flash to low pressure, lower temperature vapor once it passes through the metering device. The suction and liquid line never connect together.The liquid line brings liquid from the condenser to the evaporator. The suction line brings super heated vapor from the evaporator to the compressor. Since the unit does run, I'd have to put a gauge on it,but if I had to guess, I'd guess you have high head pressure. Check for dirt or debris on the condenser, check for proper clearance of the condensing unit and check for operation and directional rotation of the condenser fan. This could also be the result of an over charge.

The small line is your high pressure liquid line unless it is a heat pump running on heat then it is reversed and it does not suppose to be insulated.

Due to the many different questions I see about Air Conditioning, I am including this overview to help us better understand each other for trouble shooting. A basic air conditioning system has a Thermostat, Air Handler or Furnace Fan and a Condensing unit. In a split system, the condensing unit (Condenser) is separate from the furnace and usually in the back yard. When working properly, it blows hot air. It connects to the cooling part of the system by 2 copper lines. One large line and 1 small line. The part that cools the house is the "Evaporator" and is usually on top of the furnace inside the square metal box (Plenum). When the Air Conditioner is running, the large copper line should be cold and the smaller line should be warm. Common signs of low refrigerant are that both lines are the same temperature and/or frost or ice has built up on the large line at the condenser. The thermostat will normally display room temperature on till it is touched to change the setting. It could have a "Span" setting as well as times and temperatures. The operating "span" of MOST residential thermostats is 40 to 90 degrees. That means you can set it as low as 40 degrees and no higher than 90 degrees. It probably has a fan switch also. When in the "ON" position, the fan will run constantly, 24 / 7, but the condenser will still cycle on and off as needed to keep the house at set point. If you have a suggestion to include in this paragraph, please let me know. Roger

Most condensing units have low pressure safety switches in them. If your system is low on refrigerant, the compressor will run a little and shut off. When the pressures across the compressor equalize, it will come back on. This cycle will repeat on till enough gas has leaked to stop resetting the pressure switch. If this is what is happening, shut the condenser off. Short cycling will over heat the compressor. You will need a technician to find and fix the leak. Also to recharge your system when repaired. Let me know if I failed to help. Roger

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.

the A coil is froze up the low pressure side is too low, add freon

You need to replace the condensor, then take it to a shop to have the a/c system evacuated and recharged to purge moisture because the system was opened. That will cost around $150. You do not need to replace the receiver/dryer/suction accumulator even though they will tell you that you do.
go to car-part.com to find prices of condensor from salvage yards. Page with asterisk on it is the lowest priced part.

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The Refrigerant Cycle
During stabilized conditions (air conditioning system shutdown), the refrigerant is in a vaporized state and pressures are equal throughout the system. When the A/C compressor (19703) is in operation it increases pressure on the refrigerant vapor, raising its temperature. The high-pressure and high-temperature vapor is then released into the top of the A/C condenser core (19712).
The A/C condenser core, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C condenser core and enters the inlet side of the A/C evaporator core orifice (19D990).
The A/C evaporator core orifice is the restriction in the refrigerant system that creates the high pressure buildup in the A/C evaporator core (19860) and separates the high and low pressure sides of the A/C system. As the liquid refrigerant leaves this restriction, its pressure and boiling point are reduced.
The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C evaporator core, it absorbs heat from the passenger compartment airflow passing over the plate/fin sections of the A/C evaporator core. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler passenger compartment air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.
The suction accumulator/drier (19C836) is designed to remove moisture from the refrigerant and to prevent any liquid refrigerant that may not have been vaporized in the A/C evaporator core from reaching the A/C compressor. The A/C compressor is designed to pump refrigerant vapor only, as liquid refrigerant will not compress and can damage the A/C compressor.
The refrigerant cycle is now repeated with the A/C compressor again increasing the pressure and temperature of the refrigerant.
The A/C cycling switch (19E561) interrupts compressor operation before the external temperature of the A/C evaporator core gets low enough to cause the condensed water vapor (excess humidity) to turn to ice. It does this by monitoring low side line pressure. It is known that a refrigerant pressure of approximately 210 kPa (30 psi) will yield an operating temperature of 0°C (32°F). The A/C cycling switch controls system operation in an effort to maintain this temperature.
The high side line pressure is also monitored so that A/C compressor operation can be interrupted if system pressure becomes too high.
The A/C compressor pressure relief valve (19D644) will open and vent refrigerant to relieve unusually high system pressure.
Clutch Cycling Orifice Tube Type Refrigerant System
Item Part Number Description 1 19E762 A/C charge valve port (low side) 2 19E561 A/C cycling switch 3 19C836 Suction accumulator/drier 4 19703 A/C compressor 5 19D644 A/C compressor pressure relief valve 6 19D594 A/C pressure cut-off switch 7 19E762 A/C charge valve port (high side) 8 19712 A/C condenser core 9 19D990 A/C evaporator core orifice 10 19860 A/C evaporator core 11 — Low pressure vapor 12 — High pressure vapor 13 — Low pressure liquid 14 — High pressure liquid

1. Connect the R-134a A/C Refrigerant Center to the low- and high-pressure service gauge port valves.
2. Evacuate the system until the low-pressure gauge reads at least 99.4 kPa (29.5 in-Hg) (vacuum) and as close as 101.1 kPa (30 in-Hg) as possible. Continue to operate the vacuum pump for a minimum of 45 minutes.
3. Turn off the evacuation pump. Observe the low-pressure gauge for five minutes to make sure that the system vacuum is held. If vacuum is not held for five minutes, leak-test the system, service the leaks, and evacuate the system again.
4. Correctly oil match the system to verify that the correct amount of refrigerant oil is present in the system. For additional information, refer to Refrigerant Oil Adding in this section.
5. Charge the system with the specified weight of refrigerant and refrigerant oil.
6. When no more refrigerant is being drawn into the system, start the engine and select MAX A/C operation. Set the blower motor speed to maximum and allow the remaining refrigerant to be drawn into the system. Continue to add refrigerant into the system until the specified weight of R-134a has been added. Close the charging cylinder valve and allow the system to pull any remaining refrigerant from the hose. When the suction pressure drops to approximately 207 kPa (30 psi), close the charging hose valve.

Outside in the condensing unit you'll see the two copper pipes coming from the valves in the condensing unit. atach the hose from the high pressure gauge to the port in the smaller copper pipe (liquid line) and the other hose to the port of the other line (suction line) in there you check the low pressure (68psi) and if is low you can rechrge it, in the high side you should have no much more than 250psi .This pressures are for R22.