Piston and TXV sizes, AC Super heat is Here

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_ (a) Liquid line P# => T (1)                                  _ (b) Liquid line T     *Subcooling = (b) - (a)   Add will ↑, remove will ↓ . Subcooling = [10 _ 15]
_ (c) Suction line P# => T (2)                                 _ (d) Suction line T      * Superheat = (d) - (c)  Add will ↓, remove will ↑. Superheat is too high=> ice built up. CCW stern of TXV to decrease superheat. And Superheat is too low=> liquid coming back compressor, damage compressor. CW stern of TXV to increase superheat . Superheat = [10 _ 15]
* Ambient + 30 = LSAT => Head Press (↑↓) * 105 - Ambient = target SH  (↑↓)_
* (Ambient + 30)-LSAT = SC => SC (↑↓) * Ambient + 30 = Liquid (condensing) T
* Lq line T below OD ambient=> HS restriction * HS Press-LS Press>=[100_120best], or bad valves
* Target Superheat=105 - Ambient=[(3*IDWB)-80-Ambient]/2  (w/o chart) * Delta T= [12_20 F]
*Condenser coil temp high due to non cleaning of condenser/over charged gas/non condensable gas (SH ↑)   * Home refrigerator uses around 5_6 oz of R134
Non condensable gas: Low side pressure=normal, High side pressure= significant high (>300)
Reserse Valve fails: solenoid coil (check voltage,fixable), stuck in heat or cool position, stuck somewhere b/t heat/cool position
AC Low side = 40F; Cooler low side = 40F(room)-15=25F; Freezer low side= -20F
Household fridge (134A) low side not running = [60 _ 75 ]psi depending on ambient, (running)=0 Psi,. High side> low side at least 70 Psi
Oil change: vaccum, add oil high side. If bad comp, add acid first then freon  
Charge: <15 ': exact label amount; >15', add 0.6 Oz/ foot liquid line. Open low side king valve first to avoid oil enter TXV inside unit.  
TXV : =< 7/8"  => 12 O'clock;  >7/8' => 4 or 8 O'clock. Never and never 6 O'clock  

_Low Subcooling is (a) not enough refrigerant in the condenser. This can be due to undercharge, poor compression, or a metering device oversized or failing open (overfeeding).

_ Low superheat Like an overcharge condition, low superheat means too much liquid refrigerant in the evaporator and not enough vapor

_ High Subcooling is more than the designed amount of refrigerant is “backing up” or “packed” into the condenser. This can be caused by overcharge, restriction (such as a contaminated line drier or kinked liquid line), or an undersized or failing closed metering device.
_ High superheat Possible causes include a metering device that is underfeeding, improperly adjusted, or simply broken. Additional problems with high superheat could indicate a system undercharge, refrigerant restriction, moisture in the system, blocked filter-drier, or excessive evaporator heat loads.

If you are experiencing low superheat low subcooling with a TXV valve, the most common problem is that the sensing bulb (key part of the TXV valve) is either:

If Superheat is high and sub-cooling is high: Evaporator is hungry for refrigerant => Could have blockage in coil, orifice or line set, or Drier filter. If superheat is low and sub-cooling is low: Orifice could be too big, there is no orifice in the unit of the orifice is stuck and refrigerant is by-passing it. Superheat is telling you what is going on in the evaporator.