R410A Pressure Temperature Chart
R410A Pressure temperature chart or PT chart is one of the most important tool to evaluate system performance or diagnose problems.Technicians can use it along with metering gauges to check the proper functioning of Air conditioner (AC) Systems .
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Its a two column chart that shows the relation between saturation pressure and temperature .The saturation pressure is measured in PSIG and the temperature is measured in farenhite.
Keep the below points in mind
- At temperature above saturation, refrigerant becomes superheated vapor.
- At temperature below saturation,it becomes subcooled liquid.
- Saturated refrigerant must exist in evaporator and condenser of normal systems.This is due to the fact that refigerant becomes a liquid and vapor mixture in evaporator and condenser.
- Any time when you have a mixture of liquid and vapor,refrigerant must be at saturation.
- For systems with receiver,saturated refrigerant will also be found at liudid vapor interface at refrigerant level in receiver.
An example to calculate superheat
Take a reading at compressor inlet.Let us say that pressure gauge reads 16 psig and measured temperature is 47 degree farenhite.16 psig on PT chart indicates a saturated temperature of 16 degree farenhite.The amount of superheat is the difference between measured temperature and the corresonding temperature on PT chart.In this case the superheat is 47-16=31 degree farenhite.
The above example shows the scenario inside the ideal systems.In real world we have to make adjustments.
How to measure pressure at condenser coil outlet
We need to take reading at compressor discharge service valve as it is impossible to place gauge at condenser coil outlet.Let us say that meter reading is 158 psig.Assume the preesure loss to be 4 psig.Hence the pressure reading at condenser coil outlet is 158-4=154 psig.
How to measure pressure at evaporator coil outlet
We need to measure presssure at copressor suction service valve(difficult to get reading at evaporator outlet).Assume the pressure reading to be 158 psig.Assume the pressure loss to be 4 psig(usually vary between .5 to 4 psig) inside the suction lines.Just add the two number (158+4=162) to get 162 psig as the pressure at evaporator coil outlet.
R410A refrigerant operates at higher pressure than R22 ,so existing R22 systems can not use R410A.