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.

ac pressure problems
Compare the pressure readings with the pressure chart.(Photo Source: autoowls)

Matching readings means 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.


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 reasons 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.

ac low side high high side low
Check the valves on both sides.(Photo Source: hummerforums)

Before deciding to replace the compressor, other components that you may check are the pressure switch, expansion valve, and the compressor clutch. The switch is located near the expansion valve. Use an Ohmmeter to find 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.