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Common aircon issues

By autotech-nath on May 20, 2019

Nissens looks into expansion valve malfunction, diagnosis and repair. 

Impurities, such as debris or particles, are the major root cause for the precise mechanism of the expansion valve to clog and stick.

The vehicle’s AC system operation relies on two factors – the flow of refrigerant throughout the AC loop and the refrigerant’s change of state. One of the key components allowing the system to work properly is the expansion valve, which is usually installed at the evaporator inlet. Its main function is to convert liquid refrigerant into cold low-pressure gas and to regulate the flow of refrigerant. 

The expansion valve meters refrigerant flow according to evaporator temperature and the load and cooling demand of the AC system. Inside the valve, a moveable rod enables the valve to open and close a passage, allowing refrigerant to move inside it. It accurately meters the precise amount of refrigerant needed according to outside temperature and need for air conditioning. 


Improper System Operating Pressures: Pressure gauge readings that are too high or too low may be a sign of expansion valve malfunction. Normal gauge readings should be between 2 and 3 bar on the low side and 14 to 24 bar on the high side.

The expansion valve is an advanced and fragile device. As it operates under high pressures and is temperature sensitive, improper working conditions, as well as impurities inside the loop, can cause its deregulation and malfunction. 

If the expansion valve is stuck open or clogged, the AC system will not cool properly. A clogged valve will lead to too little refrigerant, increasing the pressure in the system and causing the AC compressor to overheat. If the valve is stuck open, too much refrigerant can pass through the system and into the compressor. 

If the expansion valve fails, it can cause problems with the function and performance of the AC system – if ignored, worst case scenario is expensive and irreversible damage of other system components, such as the AC compressor. 


Poor AC system performance or warm air: AC system underperformance may be a sign of a problem with the expansion valve. The AC system may begin to blow noticeably less cold than before and may even begin to blow warm air. 

Frost on AC evaporator or vents: Evaporator malfunction can cause refrigerant to flow unmetered through the vehicle’s AC system, causing the evaporator to freeze over or frost to come from the vents. Either symptom is a sign that the system is getting too much refrigerant, ultimately lowering its efficiency and performance. 

Inconsistent air flow: The air will likely alternate back and forth between different temperatures. If the air varies between cold and warm, the expansion valve should be inspected at once. 

Excessive temperatures generated at some of the loop components: A faulty or blocked expansion device will cause the system to operate under improper pressures and generate excessive temperatures. 

The easiest way to diagnose these spots is the high- pressure side’s components: Ducts from the compressor outlet to and within, and including, the receiver dryer. Temperatures above 50 °C will warn about potential blockages/malfunctions of the expansion valve. 


When you suspect a malfunction of the expansion valve, it is recommended to perform an extended system diagnostics. Troubleshooting the system operating pressures by means of pressure gauges may reveal the most common issues with the expansion valve. 

If a failure on the valve is concluded, the part should be replaced. 



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