[mustang67408]

The most common issue we have is a compressor failure. There is a speed sensor in the compressor that sends a rpm signal to the A/C amplifier which compares this to the engine rpm, if there is a difference of 200rpm or more the a/c amplifier shuts off the compressor and starts to flash the light. It can be tested with an oscilloscope to check the pattern of the compressor sensor and can be checked with a DVOM (OHM SCALE). When a compressor is failing it's rpms will vary and the speed sensor can detect this, even if the a/c seems to be functioning properly at times.
You can check CODES with one of the attachments I have provided. This circuit does not always set a code and usually you need an oscilliscope to find this issue.
These pictures are from a 2002 Camry 4 cylinder ,a/c compressor sensor from 2 weeks ago. The a/c in this car would blow ice cold MOST of the time, but intermitantly if you drove it and then shut it off for 15-30 minutes then tried to use it again, it would flash the light just about everytime. The compressor was starting to fail internally and the oscilliscope helped us find the problem.
Most dealers have an oscilliscope, but using the pdf below you can try to check codes.