Cold, low pressure refrigerant leaves the expansion valve and enters the evaporator coil. The blower fan moves warm indoor air over the coil, and the refrigerant absorbs heat from the air.
The amount of flash gas formed after the expansion valve decreases with the level of sub-cooling and the evaporator inlet pressure. The mixture of liquid and gas from the expansion valve enters the evaporator and starts to boil, because heat is transferred from the warmer secondary fluid (b-c).
The expansion valve removes pressure from the liquid refrigerant to allow expansion or change of state from a liquid to a vapor in the evaporator.
How does the refrigerant in the evaporator become cold? The refrigerant in the evaporator becomes cold through a process called vapor compression. The refrigerant is compressed and condensed into a liquid form, which causes it to release heat energy.
The expansion valve will limit how much refrigerant can pass through at one time, this results in the refrigerant dropping in pressure and temperature. The refrigerant leaves the expansion valve as a cold, saturated low pressure liquid.
The expansion valve regulates the flow of refrigerant and if it becomes damaged or worn out, it can result in leaks. To troubleshoot AC system performance and identify if the expansion valve is the culprit, you can perform a pressure test.
In order to produce a cooling effect from the higher pressure liquid, the flow of refrigerant entering the evaporator is restricted by the expansion valve, reducing the pressure and allowing isenthalpic expansion back into the vapor phase to take place, which absorbs heat and results in cooling.
As the name suggests, the refrigeration process is a cycle. We start at the compressor, go through the condenser, then through the restriction, then through the evaporator and finally back to the compressor where the cycle starts all over again.
Improper expansion valve operation can affect evaporator temperature, but expansion valves do not control the evaporator temperature and a malfunctioning expansion valve is not going to cause an evaporator to freeze up. Roger: Why not?
3 The high pressure liquid goes through the expansion valve, which reduces the pressure, and thus temperature goes below the temperature of the refrigerated space. This results in cold, low pressure refrigerant liquid.
One method is to use a pressure gauge to measure the pressure on both sides of the expansion valve. If the pressure on the high-pressure side is significantly higher than the low-pressure side, it could indicate a faulty expansion valve.
High-Pressure Readings
When the expansion valve fails, it can cause abnormal pressure readings in the AC system. If the valve is stuck open, it may result in low pressure in the evaporator, while a stuck-closed valve can cause high pressure in the system.
The economic cycle generally comprises four phases: expansion, peak, contraction, and recovery.
There are three different forces at work in a TXV: bulb pressure, spring pressure, and evaporator pressure (see Figure 4).
Compressor -> Discharge line -> Condenser -> Liquid Line -> Metering Device -> Expansion Line -> Evaporator -> Suction line -> and then back to the Compressor. The refrigeration cycle described works for all air conditioning units and chillers.
Pressure drop across the liquid line can cause the subcooled refrigerant leaving the condenser to change back to a saturated state, resulting in the metering device being fed a mixture of liquid and vapor. This will cause a reduction in the amount of liquid refrigerant fed into the evaporator by the metering device.
The compressor
Compression is the first step in the refrigeration cycle, and a compressor is the piece of equipment that increases the pressure of the working gas. Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.
– Contaminated refrigerant: A failing expansion valve can allow contaminants, such as debris or moisture, to enter the AC system, which can damage various components and reduce the overall efficiency of the system.
Final answer: The two pressures that work to close a thermostatic expansion valve are the bulb pressure, which is determined by the temperature of the sensing bulb, and the evaporator pressure, which is used to control the level of valve opening based on the required superheat.
Flooding or slugging is usually the result of the compressor providing too much cooling capacity for the load in the space or not having enough heat content in the air to evaporate the liquid refrigerant. Compressors are a vapor pump that can't handle liquid refrigerant.
The expansion valve is just one of many problems that can cause your car's A/C system to blow nothing but warm air. If the valve is stuck closed, refrigerant flow to the evaporator core will be restricted, preventing the A/C system from working as it should.