Testers for Air Conditioning Pressure Switches

A pressure switch responds to the pressure in the refrigerant circuit.

Depending on the model, it can, for example, open or close an electrical contact at a specific pressure. This allows air conditioning functions to be enabled, disabled, or controlled based on the current system pressure.

The specific function of each switch and the pressures at which it must actuate depend on the vehicle and the air conditioning system.

It is advisable to perform a test if there is suspicion that a pressure switch is not responding at the specified pressure.

Possible reasons for diagnosis include, for example:

• The air conditioning compressor does not engage
• The air conditioning system shuts off unexpectedly
• Switching behavior is implausible
• Error code related to air conditioning pressure or the pressure switch
• Suspected faulty low- or high-pressure switch

A separate pressure test can verify whether the switch actually responds at the specified pressure values.

If there are also indications of abnormal system pressure or refrigerant loss, a leak test of the air conditioning system may also be necessary.

The pressure switch is connected to a pressure pump or a pressure/vacuum pump using a suitable adapter.

The pressure is then gradually increased in a controlled manner or—for low-pressure applications—a vacuum is created.

During this process, the pressure at which the electrical switching operation occurs is monitored.

The measured value is compared with the specifications for the pressure switch in question.

The switching point is the pressure at which the pressure switch changes its electrical switching state.

Depending on its function, the contact may open or close when this pressure is reached.

For diagnostic purposes, it is therefore not only important to determine whether the switch is functioning in general, but also whether it switches at the intended pressure.

Many pressure switches have different values for the on and off points.

For example, a switch may open at a certain pressure and not close again until a different pressure is reached.

The difference between these two switching points is referred to as the switching differential or hysteresis.

Both the on and off points can be determined using a suitable testing device.

The designation is based on the pressure range monitored by the respective switch.

A low-pressure switch responds to comparatively low pressures or—depending on the application—even to pressure ranges close to negative pressure.

Medium- and high-pressure switches monitor correspondingly higher pressure ranges.

Therefore, it is not necessary to use the same test device for testing.

For low-pressure switches, Leitenberger offers the HV 90.2 pressure and vacuum pump.

It has a measurement range of -1 to +3 bar, enabling both pressure and vacuum tests.

It can be used to determine the switching points, as well as the on and off points and the switching differential, of a suitable low-pressure switch.

The Leitenberger HV 90.3 pressure pump is available for medium- and high-pressure switches.

It has a measurement range of 0 to 40 bar and features a rotary spindle and a relief valve.

This allows the test pressure to be built up and reduced in a controlled manner to determine the various switching points.

The pressure ranges to be tested vary considerably.

A pump designed for a very high-pressure range would be of limited suitability—or difficult to read—for small pressure changes in the low-pressure range.

Conversely, a low-pressure tester must not be subjected to pressures for which it is not designed.

The measurement range should therefore be compatible with the pressure switch being tested.

No. The Leitenberger HV 90.2 and HV 90.3 are supplied without vehicle- or pressure switch-specific adapters.

Both pumps have a connection with a 7/16"-20 UNF male thread.

Various HVA adapters with different thread and connection types are available for different pressure switches.

Therefore, the connection that matches the pressure switch must be selected before testing.

Not in the same way.

A conventional pressure switch changes its electrical state at a specific pressure. This allows on and off points to be determined.

Modern vehicles, on the other hand, may use electronic pressure sensors that provide the control module with a continuous electrical signal corresponding to the current pressure.

With such sensors, the electrical output signal must also be checked in accordance with the manufacturer’s instructions.

A pressure pump can generate a defined test pressure, but it does not replace the electrical measurement or diagnosis of the sensor.

For further diagnosis of the refrigerant circuit, leak testers for automotive air conditioning systems are also available.

No.

A pressure switch typically has one or more defined switching points.

A pressure sensor, on the other hand, provides a measured value or a pressure-dependent electrical signal across a wider measurement range.

In vehicle diagnostics and spare part designations, these terms are sometimes used inconsistently. Therefore, before testing, it should be clarified which type of component is actually installed.

If a pressure switch is accessible separately or is intended for external testing, its switching behavior can be tested using a suitable test pump, independent of normal air conditioning operation.

Whether the switch must be removed for this purpose or can be tested via a designated test connection depends on the vehicle and the manufacturer’s specifications.

This allows the switch’s function to be specifically evaluated without relying solely on the air conditioning system’s actual operating pressure for the diagnosis.

In this case, the electrical switching mechanism is functioning properly in principle, but the actual switching point may not correspond to the specified value.

A pressure switch that switches too early or too late can affect the operation or protection strategy of an air conditioning or refrigeration system.

The measured switching point must therefore be compared with the setpoint specified for the specific component.

No.

The devices can also be used with compatible pressure switches in other vehicle systems.

Leitenberger cites the following examples:

• pneumatic brake systems in commercial vehicles
• oil pressure switches

It is crucial that the pressure range, connection, and testing procedure are compatible with the respective pressure switch.

Before removing or opening a connection, the air conditioning system must be prepared in accordance with the manufacturer’s specifications.

In particular:

• Do not allow refrigerant to escape uncontrolled
• Use only suitable adapters
• Do not exceed the permissible test pressure of the valve
• Use the test device within its measurement range
• Check connections before pressurizing
• Relieve pressure in a controlled manner after testing

The maximum pressure a test device can generate is not automatically the permissible test pressure of the connected component.