The Reasons for AC Low Side High, High Side Low Pressure

The AC system in your car could go through all sorts of problems. One typical issue is the unit not blowing cold air, which could be punishing in hot weather. There could be several causes leading to this condition including compressor issues, low-level of refrigerant, trouble with the heater or AC controls, and others. One symptom indicating a complication in the air conditioning is AC low side high, high side low pressure.

How to Take the Pressure Readings

There are several constraints that cause this state. In fact, the temperature is directly related to the system’s pressure. You can measure the refrigerant’s pressure at a given temperature. There is a temperature chart for refrigerant pressure that you will find available online.

To gauge the pressure, hook up a gauge set to the AC system and record the pressures of both low and high sides. Check the ambient temperature and see if the pressures match the numbers on the pressure chart.

Matching readings mean that you don’t have to worry about the level of Freon. Readings higher than the chart indicate an overcharged system while lower readings confirm a low level of refrigerant and a possible leak. On the other hand, there is possibly a huge leak when the pressure is zero.

You can refer to the automotive air conditioning pressures chart below to know more:

Read more:

• A Safe and Secure Way to Flush AC System After Compressor Failure
• The Process of Replacing AC Compressor

The High And Low Side Pressure In Your Car AC System

The high side starts at the discharge side of the compressor and travels through the condenser where heat transfers to the condensation and then to the receiver dryer and finishes at the expansion valve. The compressor creates high pressure by compressing the low-pressure vapor from the evaporator so that the high-pressure steam can release heat at the condenser. This pressure change happens again at the expansion valve where the refrigerant is slowed down and changes the pressure. 

While the low side starts at the expansion valve which creates low-pressure refrigerant that travels to the evaporator where it transfers the heat from inside the vehicle and travels to the compressor where it turns into high pressure and the whole process repeats again. 

AC Low Side High, High Side Low: Why Does This Happen?

The pressure reading from the low side should be between 25 and 30 psi and the high side between 200 and 250 psi. But if you see the AC low side high, high side low, such as the low side is 100 and the high side is 150, there might be problems with any of the inner components.

The possible reason could be an excessive amount of Freon going to the evaporator. It could also be a failed thermal bulb that is unable to pick up the temperature signals or the TXV stuck to the open position.

It could be an issue with the orifice tube too. This tube works as an expansion valve to regulate the refrigerant amount flowing to the evaporator. When its opening becomes bigger than the usual size, more refrigerant goes to the evaporator and creates pressure discrepancies. The same problem arises when the o-ring seal outside of the orifice tube wears out.

Before deciding to replace the compressor, other components that you may check are the pressure switch, expansion valve, and compressor clutch. The switch is located near the expansion valve. Use an Ohmmeter to find out if it is giving the correct reading. Also, check if the compressor clutch engages and rotates the compressor when the AC is on. Similarly, the fan also has to spin when you turn the system on.

When all of these components appear to work fine and the AC low side high, high side low problem persists, you may need to change the compressor to fix the unit. However, it is always better to consult a mechanic before deciding to replace any part.

Do You Charge AC On High Or Low Side?

We will need to recharge the car AC system with a new refrigerant when the system doesn’t cool down appropriately. But the question is should you charge the car AC on either the low or high-side HVAC? You can definitely charge your car AC on the high side, however, high-side refrigerant charging sometimes is dangerous and can harm your car system. 

Watch the video to know more: 

When charging high-pressure gas, note that the engine is not working, the low-pressure valve is completely closed, and the high-pressure valve is fully open. Fill a tank with enough gas, then close the high-pressure valve. Note that it is necessary to choose a charger suitable for the system’s capacity.

Can you charge the AC system on the low side? Yes, you can. The low-side port is important because that is the point you connect to recharge the AC refrigerant. Its position is different in each vehicle, but in almost all cars, it will start at the compressor. It’s recommended that you don’t charge until it’s 75 degrees or higher to have the AC unit in your vehicle recharge.