What is the purpose of subcooling?

Subcooling is normally used so that when the refrigerant reaches the thermostatic expansion valve, all of it is in its liquid form, thus allowing the valve to work properly. If gas reaches the expansion valve a series of unwanted phenomena may occur.
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What is the purpose of superheat and subcooling?

While superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much), subcooling gives an indication of how much refrigerant is in the condenser.
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What is the importance of subcooling in a condenser?

Condenser subcooling ensures that there is a liquid seal at the condenser's bottom so the liquid line or receiver will not be fed with vapors. This condition prevents any noncondensables, like refrigerant vapor or air, from leaving the condenser's bottom and entering the receiver or liquid line.
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What happens if you have too much subcooling?

If the subcooling is too high, the system will be overcharged, reducing performance, efficiency, and ultimately damaging compressor valves and start components.
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What does low subcooling indicate?

Low Subcooling is an indication that not enough refrigerant is contained or “packed” in the condenser. This can be due to undercharge, poor compression, or a metering device oversized or failing open (overfeeding).
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Superheat and Subcooling Explained! How to Easily Understand!



How is subcooling different from superheat?

Superheat is defined as the amount of heat added to a vapor above its boiling point. Subcooling is defined as the amount of heat removed from a liquid below its condensing point.
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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".
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What is the purpose of superheat?

Superheat is critical in HVAC because it ensures the liquid refrigerant is boiled off before it leaves the evaporator and heads to the compressor. Even small amounts of liquid can cause detrimental damage to a compressor in an HVAC system.
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What happens if superheat is too high?

Too high of a superheat can cause the heat of compression to increase, causing the temperature at the discharge valves to increase. If the temperature increases beyond its safe operating temperature, it will cause damage to the compressor.
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What is a normal subcooling temp?

Typical systems will run between 10F and 20F of subcooling. If lower than 10F, the system is likely undercharged.
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How do you adjust subcooling?

The temperature that you read with the thermometer should be lower than the saturated condensing temperature. The difference between the measured liquid line temperature and the saturated condensing temperature is the liquid subcooling. Add refrigerant to increase subcooling. Recover refrigerant to reduce subcooling.
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What is normal subcooling 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.
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What causes high subcooling and high superheat?

If you notice a high superheat and an excessively high subcooling, this is likely a system with a liquid line restriction that is overcharged. A previous technician has likely added pounds of refrigerant into the system in an attempt to raise the low side saturated temperature to a level above freezing.
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Does low refrigerant cause high superheat?

Excessive or high superheat is an indication of insufficient refrigerant in the evaporator coil for the heat load present. This could mean that not enough refrigerant is entering the coil or this could also indicate an excessive amount of heat load on the evaporator coil.
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Does low airflow cause high superheat?

HIGH SUPERHEAT LOW SUCTION PRESSURE

Another possible reason for low suction pressure high superheat is the insufficient amount of heat entering the evaporator which could be because of limited airflow or due to a dirty/plugged evaporator.
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What is the formula for subcooling?

Calculate the subcooling as follows: subcooling = CT – T. For a refrigerant blend use the saturated liquid (bubble) temperature as the condensing temperature. Subcooling will not usually occur in the condenser unless liquid backs up in the condenser.
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What should my superheat be with a TXV?

The typical TXV comes factory set for 8-12 degrees of evaporator superheat, which in most cases should be fine. What is the correct setting for evaporator superheat? While it is true lower superheat will make the evaporator more efficient, we need to be more concerned with the compressor or total superheat.
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What is a good target superheat?

The minimum recommended target superheat for most charts is between 4F to 5F for the environments with low indoor wet bulb and high outdoor dry bulb.
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What should pressures be on 410A?

For R-410A, a working pressure capability of at least 400 psi is recommended (this includes recovery cylinders). Standard DOT recovery cylinders rated for 350 psi should not be used.
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What causes TXV to hunt?

Common reasons for TEV hunting

Oversized valve – The expansion valve may be oversized for the application or operating condition of the system. If the valve capacity significantly exceeds the requirements of the system, when the valve attempts to adjust to system load it overcompensates because it is oversized.
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What would cause 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.
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What causes high superheat low subcooling?

If superheat is high and sub-cooling is high: Could have blockage in coil, orifice or line set. 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.
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Can you check subcooling in heat mode?

Subcool and superheat can still be checked in heat mode, the problem is since there are rarely any set guidelines, it is difficult to tell when the charge is set correctly by simply checking subcool or superheat alone.
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