HEM Data Products

Diagnosing Intermittent Problems

Intermittent problems are often the most difficult and frustrating problems to diagnose and repair. Using a Mini Logger from HEM Data, a Mercedes-Benz technician was able to fix some rather challenging problems.

The first involves an intermittent air conditioning issue, and the second an intermittent transmission problem. This eNewsletter describes the A/C solution and the next eNewsletter will cover the transmission solution.

The customer stated that intermittently the A/C vents blow warm air for up to 2 to 5 minutes, then revert back to normal cool air. After two unsuccessful attempts to fix the problem, the technician installed the logger to monitor the vehicle under normal operation.

After a week the customer returned with the data. It turned out that there were two problems, which made diagnosing the problem more challenging.

  1. There was rat damage/ rat bite marks in an obscure area and very intermittently copper wire strands shorted causing a loss of actuation current due to a short, and
  2. Secondly, there was an internal fault in the wobble plate compressor not building pressure, even though full actuating current was applied. The DawnPlot software below actually shows both issues captured.

Plot showing current loss and pressure drop
*Click image to enlarge*

The technician repaired the wires and replaced the wobble plate. This restored the A/C to normal operation.

J1939 Mini Logger™ OBD Mini Logger™ DAWN Telematics™ DAWN™ Software ADAQ Mini™ DAWN Dashboard™