Low Discharge Superheat: Process, Formula, Work, Example And Exhaustive FACTS

In this article we will discuss about the “Low discharge superheat” and its related factors.

The Low discharge superheat is when the refrigerant liquid flooding to the compressor or in the screw compressor in the very low oil temperature. The insufficient amount of air flows through the evaporator coils causes low discharge superheat.

With a high ambient temperature the refrigerant liquid go back to the compressor which causes the leakage to the heat exchangers and liquid injection device if it is fitted. This condition also point to an Actuator or Check valve issue. A dirty air filter, evaporator coil or air flow causes discharge measure low. The heat which is carried by the coils is low which result in low discharge superheat.


The low discharge superheat can be obtaind by the following,

  • At first we need to run the refrigeration system minimum for 10 min.
  • When the system running for a while we have to attach the pipe clamp thermocouple in one side of the refrigerant line which actually separate the thermal expansion valve and the condenser discharge valve.
  • Connect with the refrigerant manifold gauges with discharge service valve.
  • Read refrigerant manifold gauge to check the discharge service valve.
  • Check the thermocouple temperature using a digital thermometer.
  • Measure the pressure chart and temperature for the refrigerant.
  • Now need to turn over the condenser pressure reading to a condenser saturation temp.
  • Pressure takes from the thermocouple and the temperature of the condenser saturation from it.


The low discharge superheat is calculated in the way as any other discharge superheat calculated on a system, by measuring the low discharge superheat and have to subtract the suction superheat and then then leaves with a figure of how much low superheat the compressor has given through compression and mechanical/electrical inefficiencies.


Prevent damage the machine from worn rings, acid formation and oils breakdowns and make it run more effective.


Let, the Discharge Temperature = 152, Condensing Sat. Temp. = 91

Then the discharge superheat would be = 61

Exhaustive facts:

In the discharge superheat refrigerant is saturated with oil causes low discharge superheat. Low discharge superheat can causes low temperature to the compressor, if the condition goes more low and low then it could damage the compressor too.

What does a low superheat indicate?

The low discharge of a system means refrigerant liquid floods to the compressor for the load is present through the evaporator coil.

When excess amount of refrigerant is enter into the coil or excessive amount of heat present into coil to vaporize the refrigerant properly,that time this condition appear.

Read more about Low Superheat: Important Terms and 3 FAQs

What causes low discharge superheat?

  • Flooding to the compressor with the refrigerant liquid through the evaporator coil. The situation mostly happened when the expansion valve overfeeding to the evaporator or faulty of an actuator.
  • Pressure is too high.
  • Low evaporator air flow.
  • Temperature is low.
  • The shape of the system is over sized during discharge of a superheated liquid.
  • Reduced airflow through the evaporator.
  • Due to low cooling water flow or dirty tubes the refrigerant charge may be excess.
  • Over charged of refrigerant liquid or oil.

Low discharge superheat trane chiller:

With the help of the compressor’s discharge temperature the inside condition of the refrigeration or air conditioning system easily can be recognize. In other term the discharge temperature describe as a measurement of the superheated refrigerant’s vapour temperature.


Discharge Superheat = Temperature of discharge connection – Saturated temperature of the liquid line.


This is used to point an actuator or check the valve issue. The Trane chillers are used to system for improve the efficiency mechanical or electrical to the compressor,deliver the correct amount of the temperature, humidity. During the flooding of the refrigerant liquid or oil the sound of the system is increases, with the Trane chillers the sound became less which impact is good for the environment .The Trane chillers deliver ventilation for the space and also helps to minimize the operating cost.

York yvaa low discharge superheat:

The low discharge superheat faults due to reason of the quantity of oil in the oil separator causes York Yvaa low discharge superheat. For this reason the oil charge is reduced in these specific circuits to correct the nuisance superheat trips. The change is only applicable to the circuits.


  • The first step is to identify the unit and the amount of the oil. The oil should be taken as that much quantity with which it could be removed as per the corresponding compressor.
  • As per the correct size the compressors are verified.
  • Need to walkout the unit.
  • After that need to discharge the unit.
  • A container is used which should be have measuring indicators gradually.
  • In the next step required oil is removed from the container.
  • The oil is separate from the compressor on the oil line.
  • In the starting if the refrigerant was removed from the low discharge superheat then make sure to correct the refrigerant level.
  • Adding the adjusted refrigerant to the system.
  • Apply unit to the system.
  • For about one hour the unit should be operate at full load.
  • Finally need to note down the oil level from the oil separator.

York low discharge superheat:

Low discharge superheat usually the situation occurs because of overcharge of refrigerant or overcharge of oil. Both condition gives lower discharge temperature. Once the refrigerant is saturated with oil low discharge will continue to occur.

Low discharge superheat sensor:

In the low discharge superheat all chillers will have a certain amount of the oil in the refrigerant, a little amount of oil is good but the system but too much is not good for the entire system. An excess amount of present of oil can cut blade from the impeller and reduce the efficiency of the compressor and also minimize the percentage of the heat transfer. For the recovery from this unwanted situation in the low discharge superheat’s chillers recovery equipment is needed, the recovery equipment is called the low discharge superheat sensor.

The main purpose of the sensor is to sense the oil which is float on the top of the refrigerant. The low discharge superheat condition is happened when the refrigerant liquid flooding into the compressor, or in the case of screw compressor, low cold oil temperature.

Low discharge superheat in chiller :

In the application field after doing the investigation we could find that the performance of the chillers attached with an electronic expansion valve. The chillers mainly work in steady state and transient condition. .The chillers capacity works in both hot and cold starts.

In low pressure the chillers start to work, at this condition the refrigerant enter to the evaporator. In case of low discharge superheat the capacity is very fast. In the cooling condition the chillers leading to low off/on cycling losses. The expansion valve works on the both steady and transient state of the chillers.

The capacity of the chillers is about 25 kW.  The chillers mainly consists four components. The components are compressor, evaporator, expansion unit and condenser. Every chillers system has refrigerant.

What is good discharge superheat?

The temperature of the ideal discharge superheat is about 10K-15K.

Frequently Asked Questions:

Q.What is low discharge superheat?

When a little amount of air could passes to the system for the reason of stopping the head load entry through the evaporator coils,which occur low discharge superheat.

The low discharge indicates that the quantity of refrigerant liquid or oil present in the compressor.

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