Category: Thermal expansion valve

Yellow Jacket manifold gauges

Auto A/C Compressors have evolved over time and the old, fixed displacement compressor has been replaced by more efficient variable displacement compressors. Pressure controlled variable displacement compressor and Electronically Controlled Variable Displacement Compressor (ECV) react in different ways compared to fixed displacement compressors when air conditioning restrictions and other common automotive a/c faults happen. Failure to identify the type of a/c compressor in the vehicle at the beginning of the diagnostic procedure could lead to unnecessary, expensive and in most cases time consuming repairs. A restricted Thermal Expansion Valve creates Manifold gauge readings that could lead to chasing a/c system leaks, unnecessary auto a/c compressor and sensor replacement.

How do I know if my compressor or expansion valve is bad?

Manifold Gauge readings

Low side LOW        High side LOW

A restricted Thermal Expansion valve gauge readings will be different in the newer Pressure controlled variable displacement air conditioning compressor.

 When a restriction in the refrigerant flow caused by a Thermal Expansion Valve (TXV) fault happens, the Pressure controlled variable displacement compressor will try to compensate the change in refrigerant pressure from the TXV by adjusting the compressor internal control valve, and keep the compressor crankcase pressure at a value where the swash plate angle based on the low side pressure is prevented from going into the condition where you see a manifold gauge vacuum reading. The manifold gauge reading in this type of system will show Low side gauge reading low and High side gauge reading low. It could be erroneously diagnosed as a weak compressor problem.

Low Side into Vacuum         High Side LOW

A restricted Thermal Expansion Valve (TXV) gauge reading on an Electronically Controlled Variable Displacement Compressor will be different due to the logic the Powertrain Control Module uses to operate and control the a/c compressor. The PCM will receive inputs from the evaporator temperature and will command signals to the ac compressor electronic control valve to adjust pumping capacity accordingly. When the TXV fails or is restricted the evaporator temperature will increase and that increase value will be sent to the PCM which in turns will increase compressor pumping capacity to 100%.The Electronically Controlled Variable Displacement Compressor will operate similar to an old ,Fixed Displacement A/C Compressor and the Manifold Gauges will show Low Side going near 0 Psig or into a vacuum reading.

How do I know if my compressor or expansion valve is bad?

  • The type of system must be identified
  • The type of a/c compressor must be identified
  • Manifold Gauge Readings must be checked
  • PWM signals to the ECV must be inspected

Avoid unnecessary expensive repairs.

The air entering the cab is only slightly cool, and there are bubbles visible in the sight glass. there is usually about an 95% chance the restriction is expansion valve failed in the closed position related, 4% chance it is drier related and 1% chance it is somewhere else along the system or  an internal drier desiccant bag rupture leading to a/c system contamination and restricting the metering orifice of the expansion valve.

Call Us today if your A/C is experiencing this symptoms! The correct diagnostic procedure will save you TIME and Money. Auto A/C Repair LLC. offers mobile a/c inspection in Hialeah,florida.

thermal expansion valve

Auto A/C Expansion Device Repair.

The Auto A/C Expansion Device in your vehicle may need to be repaired if it is not controlling the flow of refrigerant into the evaporator core correctly. All A/C systems meter the refrigerant into the evaporator core for the purposes of controlling the evaporator temperature.

Types of metering devices.

Depending on the system, it could be a variable or fixed style metering device. It could be a Thermal Expansion valve or Fixed Orifice Tube.

Types of Metering Device and control type.

The variable style metering device: (Thermal Expansion valve, TXV ) controls the flow of refrigerant by sensing the temperature of the evaporator and adjusting the amount of refrigerant entering the evaporator by varying the size of the metering device opening.

The fixed system: (Fixed Orifice Tube ,FOT) uses a fixed metering device and controls the amount of refrigerant entering the evaporator core by controlling the operation of the compressor itself.

When should I replace the expansion valve or fixed orifice tube in my vehicle?

Orifices tube should be replaced  any time the A/C system is serviced and particularly if the A/C system is found to be contaminated.

Thermal expansion valves are typically replaced if they fail to operate correctly.

Do you need assistance replacing your A/C expansion device ?

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