Check the Return Air Temperature at the air handler or furnace. Return Air Temperature below 64 deg. will cause low pressure issues.
Final answer:
Several conditions can lead to a decrease in suction pressure in HVAC systems, including a restricted liquid line filter drier, a dirty indoor air filter, and an underfeeding metering device. Each of these factors affects refrigerant flow and heat absorption processes.
If your txv is bad on the outdoor unit your suction pressure is in the outdoor coil and the txv starves the coil and your suction pressure will pump down just as if the indoor txv where to lock up in cooling. Your head pressure is not going to raise the levels that they are as quickly as they are with a mis-sized coil.
Dirty/damaged or iced up condensers would cause low suction pressure, not high suction and certainly not high head pressure.
Low suction is caused by low refrigerant, poor airflow, such as a plugged return air filter.
There are many causes of low suction pressure, including low indoor temperature, dirty filters, restricted ducts, undersized ducts, closed dampers, frosted coils, restricted refrigerant line, restricted piston, restricted strainer, and bad indoor evaporator motor.
The TXV cannot be adjusted open or closed, it is a modulating valve. Turning the adjustment stem clockwise will only increase spring pressure causing a higher superheat. Turning the adjustment stem counterclockwise will decrease spring pressure reducing superheat.
One of the most common causes of low suction pressure is loss of critical refrigerant charge caused by small leaks over time.
Overcharging leads to overfeeding the evaporator with refrigerant, which leads to higher suction pressure. Another possibility is having oversized EXV causes an overfeed to the evaporate, which increases your suction pressure.
Low Suction Pressure: Suction pressure is the pressure in the evaporator or the low side of the refrigeration cycle where the refrigerant absorbs heat. Symptoms: Poor cooling performance, freezing of the evaporator coil, and abnormal noises from the compressor.
A pressure reducing valve creates and holds a downstream pressure set point. Oil and gas producers use a pressure reducing valve (also called a "pressure reducing regulator") as a suction controller or recirculation valve on a compressor, or to supply fuel gas.
To check for a leaking valve, measure the difference in temperature between the suction line from the evaporator and the permanent suction line on the reversing valve (usually the middle line on the bottom). The temperature difference should not be more than 3F.
Insufficient suction pressure.
Low pressure at the pump inlet can cause cavitation, which occurs when the liquid entering the impeller eye drops below its liquid vapor pressure and vaporizes to form bubbles.
A clogged valve is typically easy to fix because many TXV parts will include a strainer that is pulled out without the need to remove the whole valve. With the strainer pulled out and cleaned, the clog issues should go away.
If the TXV fails closed it can be said to be “underfeeding,” which means not enough boiling refrigerant is fed through the evaporator coil and superheat will be too high at the evaporator outlet.
It is important to have it cleaned yearly. The condenser's main job is to release the heat that the indoor coil has removed from the home. With a dirty condenser, less heat will be able to be removed from the outdoor coil. This increases the heat in the condenser and increases the pressures.
You can either use a commercial coil cleaner or make your own by mixing water and vinegar in a spray bottle. Spray the mixture onto the coils and let it sit for five to ten minutes to break down any stubborn dirt.