What is the subcooling method?

Subcooling Formula: Saturated Temp – Actual Line Temp = Subcooling So what does this mean? Simply put, subcooling is the lowering in temperature of the liquid refrigerant in the condenser coil. On a split system air conditioner, the condenser coil is in the outdoor unit.

When should I charge my subcooling?

Expansion valve systems are normally charged by using the subcooling method. Liquid sub-cooling is required so that you have only liquid entering the expansion valve with no bubbles present. Vapor bubbles present in the refrigerant will cause low refrigerant flow.

How do I calculate subcooling?

Refrigerant liquid is considered subcooled when its temperature is lower than the saturation temperature corresponding to its pressure. The degree of subcooling equals the degrees of temperature decrease below the saturation temperature at the existing pressure. Subcooling Formula = Sat. Liquid Temp.

Do you use superheat or subcooling for TXV?

An air conditioning unit with a thermostatic expansion valve (TXV) is charged to the subcooling of the liquid line leaving the condenser because the superheat is fixed. The superheat is fixed at 8°F to 12°F in most residential air conditioning systems.

When would you charge via subcooling instead of superheat?

To determine the type of metering device, view the image below. If the metering device is a fixed orifice such as a piston or capillary tube, the refrigerant charge of the system can be checked with Total Superheat. If the metering device is a TXV then the refrigerant charge can be checked with Subcooling.

What is the normal subcooling?

between 10F and 20F
Subcooling can still be used to identify an over or under-charged system. Typical systems will run between 10F and 20F of subcooling. If lower than 10F, the system is likely undercharged. If over 20F, the system is probably overcharged.

What is refrigerant subcooling?

Definition of Subcooled Refrigerant A sub-cooled liquid refrigerant is at a temperature below (colder-than) the temperature at which the refrigerant would evaporate (“boil” or change from a liquid refrigerant to a gas – also called the refrigerant saturation temperature).

How much subcooling do I need for 410a?

Most heating and cooling systems should operate at a superheat of 10F at the evaporator and between 20F to 25F at the compressor. if your HVAC system has a thermostatic expansion valve (TXV), the subcooling should be between 10F and 18F.

Do you use subcooling with a TXV?

Subcooling on systems that use a thermostatic expansion valve (TXV) should be approximately 10°F to 18°F. Higher subcooling indicates excess refrigerant backing up in the condenser. On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added.

What causes high subcooling?

Excessive subcooling means the refrigerant was cooled more than normal. Possible explanations include overcharging, a restricted metering device, maladjustment (underfeeding), or faulty head pressure control during low ambient conditions.

Why is it called subcooling?

The term subcooling (also called undercooling) refers to a liquid existing at a temperature below its normal boiling point. For example, water boils at 373 K; at room temperature (293 K) the water is termed “subcooled”.

What is normal subcooling temp?

Generally speaking, 10-12° of subcooling at the outlet of the condenser coil is most common. However, you must look for the proper design subcooling for the particular system you are working on. Some systems will require subcooling readings of up to 16° for maximum efficiency and capacity.

What is subcooling on a split system AC?

Simply put, subcooling is the lowering in temperature of the liquid refrigerant in the condenser coil. On a split system air conditioner, the condenser coil is in the outdoor unit. While the system is running, refrigerant exits the vapor compressor and travels through the condenser coil to reject heat into the outdoor air.

How do you calculate subcooling pressure?

Subtract the two numbers to get the subcooling. For example, 275 psi head pressure on an R-22 system converts to 124°F. The liquid line temperature is 88°F.

What happens if the subcooling level is lower than the target?

If the actual subcooling is lower than the target subcooling, the unit’s refrigerant level is undercharged. There is a leak that needs to be fixed and refrigerant will need to be added. If the actual subcooling is higher than the target subcooling, the unit’s refrigerant charge level is overcharged.

Why does the subcooling increase when adding refrigerant to TXV?

On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added. If the superheat doesn’t change, and the subcooling increases, the problem is with the metering device.