Air Conditioning Diagnosis
by Temperature Measurement
Efficient operation of a vehicle’s A/C System is dependent on the change of state of the refrigerant within the
System by the pressure changes created by the compressor pumping the refrigerant around the system loop.
As the Refrigerant changes state within the system this change of state is directly linked to the temperate of the
Refrigerant in that section of the A/C system loop. Knowing this relationship of Pressure / Temperature allows us to
use this as a basic diagnosis tool for system analysis.
Technicians can use temperature diagnosis as a cost effective and reliable method to troubleshoot a system to
analyse what potential issues are in the system and where they could be physically located.
Location of components in the particular part of the system loop will determine what the temperature range should
be in that component for it to be operating correctly. Temperatures outside this range, either too Low or High
can be evaluated to indicate potential problems within that component or other components that can have a
flow on effect on the area tested or other potential issues such as contaminated or wrong refrigerant, too much/Incorrect Oil, Dye or even remnant Flush.
Poor Performance of the system and therefore cabin Climate Control in the vehicle is the ultimate result for any component/contamination issue in any automotive A/C loop
Before commencing any PT or Pressure Temperature testing the technician should be able to have sufficient
access to critical components and lines in the refrigerant loop that will enable temperature measuring and
familiarize themselves with the system components and their location. The engine must be running at idle and at
Operating temperature 80-90C with the A/C system set to cold with fan at max setting.
Quality Temperature measuring devices are to used, these can be either Infra-red or with a sensing probe.
There are a number of specific locations that temperature can be measured, these can be on refrigerant lines,
component surfaces and at inlets and outlets of vents etc.
Temperature Measurement Points Temperatures with Infra-red Thermometer
Evaporator Surface * 0-5°C
Tx Valve On Surface 2-5°C
Compressor Suction Line - Evap To Compressor Line 15-20°C
Receiver Dryer Directly On The Unit 30-50°C
Condenser To Receiver Dryer Line 30-50°C
Compressor Directly On The Unit 60-90°C
Condenser Outlet ...To Receiver Dryer 40-60°C
Condenser Inlet ...From Compressor 60-90°C
Condenser - Difference in temp, inlet to outlet comparison
*Evap Temp may vary with later styles for R1234YF due to thicker walls
Common Issues that will cause the component being tested
to be outside its normal temperature range
• System improper charge – too low or to high amount of refrigerant
• Improper use of additives – mainly excessive use of UV dye causing the system overpressure
• Component and system inner blockages and restrictions – caused by impurities, debris, moisture or corrosion in
the system, improper use of additives (leak stop agents), consequence of overheating and carbonized lubricant
particles – mostly exposed to clogs are expansion valve, receiver-dryer and condenser (thin micro tubes)
• Condenser Fan not Operating
• Lack of Cabin air circulation – blocked Evaporator, Cabin Filter, damaged on non-functioning air directional flaps.
• Faulty compressor, Compressor control valve – clutch/valves or operation in general
• Faulty or blocked internally or externally condenser – restricted heat exchange caused by missing fins, fin
corrosion, blocked surface from mud leaves etc. leakages, bent tubes and fins, accident damage