Test and Diagnostic Equipment for Automotive Air Conditioning Systems

Frequently Asked Questions About Testing and Diagnosing Vehicle Air Conditioning Systems

Automotive air conditioning systems must operate reliably, be leak-free, and be compatible with the refrigerant used. Various testing methods are available for professional diagnostics—ranging from pressure leak testing and tracer gas leak detection to testing pressure switches and temperature differentials.

• What tests can be performed on a vehicle's air conditioning system?

  Depending on the fault symptoms and the air conditioning system, different tests may be required.

  Typical diagnostic and testing procedures include, for example:

  • Leak test of the refrigerant circuit
  • Pressure testing on the high- and low-pressure sides
  • Leak detection using tracer gas
  • Testing of low-, medium-, and high-pressure switches
  • Temperature and differential temperature measurement
  • Inspection of lines, couplings, and connections

  Which test should be performed depends on the vehicle, the refrigerant used, and the manufacturer’s specifications.

• What is the difference between a leak test and leak detection?

  During a leak test, the first step is to determine whether the air conditioning system—or a part of the system—maintains the specified test pressure.

  If the pressure drops within the specified test period, a leak is suspected.

  The leak test thus first answers the question:

  Is the system leak-free?

  Leak detection goes one step further and answers:

  Where is the leak located?

  For this purpose, for example, forming gas can be used in conjunction with an electronic leak detector.

• Why shouldn't a leaky air conditioner just be refilled with refrigerant?

  If an air conditioning system has lost an amount of refrigerant that exceeds normal levels, the cause of the loss should first be determined and the leak repaired.
  
  Refilling the system without first making the necessary repairs may result in further refrigerant leakage.
  
  For fluorinated refrigerants, the applicable legal requirements must also be observed.
  
  The specific procedure depends on the vehicle, the refrigerant, and the manufacturer’s specifications.

• What refrigerants are used in automotive air conditioning systems?

  In the automotive sector, the following refrigerants are particularly relevant:

  • R134a
  • R1234yf
  • R744

  These systems differ, among other things, in terms of pressure levels, connections, and safety requirements.

  Therefore, test equipment, hoses, and couplings must only be used for the refrigerants or pressure ranges for which they are intended.

• What should you pay special attention to with air conditioning systems that use R744?

  R744 air conditioning systems operate at a significantly different and much higher pressure level than traditional R134a or R1234yf systems.
  
  Therefore, testing and servicing require equipment, hoses, couplings, and safety components specifically designed for this purpose.
  
  A test device designed for R134a or R1234yf must not be used for R744 without further consideration.
  
  The Leitenberger KLDS 05, for example, is designed for leak testing on R744, R1234yf, and R134a systems.

• What is forming gas, and what is it used for in air conditioning diagnostics?

  Forming gas is a test gas that can be used for leak detection.
  
  A mixture of nitrogen and a small amount of hydrogen is often used when testing air conditioning systems.
  
  The gas is introduced into the empty or appropriately prepared air conditioning system.
  
  An electronic leak detector can then detect the hydrogen escaping from a leak.
  
  This allows a previously identified pressure loss to be pinpointed.

• What is the difference between a nitrogen test and a forming gas test?

  Nitrogen can be used to pressurize the air conditioning system to a specified pressure and check for pressure loss.

  This allows you to determine whether the system maintains the test pressure.

  Forming gas can also be used for leak detection.

  In this process, the escaping test gas at the leak is detected using a suitable electronic leak detector.

  In simple terms:

  Nitrogen/pressure test: Is the system leak-tight?

  Forming gas leak detection: Where is the leak located?

• Is a vacuum test sufficient to reliably check an air conditioning system for leaks?

  A vacuum test can provide information about the condition of a system, but it does not simulate the same conditions as a pressure test.
  
  Components, seals, and connections may behave differently under negative pressure than under positive pressure.
  
  Therefore, a pressure test using a suitable test gas may be required for a targeted leak test after repairs.
  
  The vehicle manufacturer’s specifications and the prescribed test procedure are decisive.

• Can contrast agents be used to detect leaks?

  Contrast agents or UV additives continue to be used in certain applications in automotive air conditioning systems.
  
  However, it is crucial that a known leaking system not be filled solely with refrigerant in order to subsequently search for the leak by observing escaping refrigerant or contrast agent.
  
  Whether and in what form contrast agents may be used—or are specified by the vehicle manufacturer—depends on the specific system and test procedure.
  
  For targeted testing of an empty or prepared system, a pressure test using nitrogen or Formier gas is recommended.

• How does electronic leak detection using forming gas work?

  After filling the prepared system with forming gas, the lines, connections, and components are inspected using a suitable electronic leak detector.
  
  The leak detector reacts to the hydrogen contained in the test gas.
  
  At a leak, the test gas escapes and can be detected by a visual or audible signal.
  
  A flexible or long probe can also be used to inspect hard-to-reach areas.

• Why should a leak test be documented?

  A documented inspection makes it easier to track the workshop process that was carried out.

  An inspection report may include, for example:

  • Date and time
  • Duration of inspection
  • Pressure readings
  • Inspection results

  This is particularly helpful for repairs, warranty claims, customer communication, and internal quality control.

• How important is the air conditioning system in hybrid and electric vehicles?

  In hybrid and electric vehicles, the climate control system can perform additional tasks related to thermal management in addition to regulating the cabin temperature.
  
  Depending on the vehicle, the air conditioning system or refrigerant circuit can, for example, help regulate the temperature of the battery or other electrical components.
  
  As a result, a malfunctioning air conditioning system can affect not only cabin comfort but also other vehicle functions.
  
  However, the specific system architecture varies greatly among vehicle manufacturers.

• How can you check the cooling capacity of an air conditioner?

  One option is to measure the temperature at appropriate measurement points.
  
  For example, a two-channel thermometer can be used to measure two temperatures simultaneously and compare them directly.
  
  This makes it possible to assess temperature differences between different points in the climate control system or between the ambient temperature and the outlet temperature.
  
  The measurement conditions and setpoints depend on the respective vehicle manufacturer.

• What is the function of pressure switches in an air conditioning system?

  Pressure switches monitor defined pressure ranges within an HVAC or refrigeration system.

  Depending on the system, they can, for example, trigger an electrical switching operation when the pressure is too low or too high.

  During diagnostics, the following can therefore be checked:

  • at what pressure the switch responds,
  • when it resets,
  • and what the switching differential is.

  Different test ranges are required for low-, medium-, and high-pressure switches.

• How do you test an air conditioning pressure switch?

  The pressure switch that has been removed or is intended for testing is connected to a pressure pump or a pressure/vacuum pump using a suitable adapter.
  
  The pressure is then adjusted in a controlled manner.
  
  During this process, the on and off points, or the switching differential, are determined and compared with the manufacturer’s specifications.
  
  For low-pressure switches and medium-/high-pressure switches, appropriate test equipment is used based on the different pressure ranges.

• What kind of air conditioning test equipment makes sense for a repair shop?

  The equipment should be tailored to the vehicle fleet and the air conditioning services offered.

  The following items may be particularly useful for professional diagnostics:

  • Air conditioning leak detector
  • Pressure reducer for test gas
  • Suitable hoses and refrigerant fittings
  • Forming gas leak detector
  • Pressure test pumps for air conditioning pressure switches
  • Digital temperature gauge
  • Air Conditioning Service Accessories

  Workshops that service vehicles with R744 also require testing equipment specifically designed for the higher pressure levels.

• What safety rules apply during an air conditioning inspection?

  Air conditioning systems can be under high pressure. Depending on the refrigerant, additional chemical, physical, and safety requirements may apply.

  Therefore, the following applies in particular:

  • Properly prepare the system before opening it
  • Do not release refrigerant in an uncontrolled manner
  • Use only equipment suitable for the respective pressure range
  • Use appropriate couplings and hoses
  • Select the test pressure according to the manufacturer’s specifications
  • Use personal protective equipment
  • For hybrid and electric vehicles, observe additional high-voltage requirements

  Work on the refrigerant circuit may only be performed by appropriately qualified personnel and in accordance with applicable regulations.