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Help! My Compressor won't start!

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If you have installed a system but cannot get the compressor to start, this is how to diagnose.

Firstly, use the 'putty' software so you can access the test features of the ECU.   You can get the latest Electrocooler software here.

Test Steps:

1.  After extracting the zip files to you computer,  start the Electrocooler software by double clicking RunMe in the top level Electrocooler folder


2.  The following screen appears.  You may be prompted to plug (or replug) in the USB cable diagnostic cable.  The 'Status' line should say Ready on COMX  ( X can be any number ).  If it does not, check your Windows Device Manager and resolve any driver issues.  Sometimes swapping to a different USB port can fix this.


3.  Plug the 3.5mm jack into the Electrocooler ECU and press 'Start Terminal',  Switch the car ignition on.  A black screen appears with scrolling numbers.   (Have a look at our Setup and Test manual for more info on the numbers but you don't need that info for this test).  Press return a couple of times to stop the numbers scrolling and get the > prompt.

Now type CMP=50 and press return.  if you mess up the typing, press return again and type the command again(backspace isn't supported by the ECU).  The ECU responds CMP:OK (it will respond UNK for unknown if you mistyped)  

The main contactor relay will click and the compressor should start.  Wait at least 30 seconds - some compressors have 30 second restart delay.



Reasons for non start:

1)  The main power feed is less than 11.0V - the compressor has under voltage protection.   The 12V power feed is from the thick red wires that go through the large contactor relay.  It is important to look at this voltage when the compressor tries to start - is the voltage dropping?  Start the engine to be sure that the voltage doesn't 'sag'.

2) Faulty or worn contactor.  The contactor is a service item - it will wear eventually but should have a service life of 5 years but this depends on use.  If you suspect a contactor fault, connect the compressor directly to the battery by joining the two cables together.   We have also seen some issues with cheap battery isolators not being able to provide the power required by the compressor.  In this case the compressor may try to start and shut off immediately.

3) Power / signals not present.   This is how to test the signals that drive the compressor:

Find and unplug the the compressor control cable from the ECU


On the ECU side, the signals are:


RED - 12V



Enter the command CMP=50 to enable the contactor relay and activate the signal lines.  Using a multmeter, check the following pins.  For these checks the -ve multimeter should always be on GND (Blue)

Check POWER:   Should measure Battery Voltage (~12V) between RED and BLUE.  If there is no voltage here then check the main harness yellow and yellow/black wires for 12V.


Check ENABLE:   Should measure Battery Voltage (~12V) between YELLOW and BLUE.  


Note:  Early ECUs used a 5V signal - in some cases we found this was not enough voltage to start the compressor.  If you have a 5V enable and have a starting issue you can permanently wire the compressor enable wire (orange on the compressor connector) to 12V as a work around.  This will not affect the operation of the system.


Check SPEED/DUTY:   With a duty cycle of 50% (CMP=50) should measure ~6V between GREEN and BLUE



Alternatively to check SPEED/DUTY, if your meter has a Frequency function (Hz),  you should measure ~400Hz between GREEN and BLUE


An oscilloscope can also be used to verify the speed/duty signal (again, between GREEN and BLUE).  ~400Hz with amplitude ~12V.







Notes on compressors and their firmware

We use two types of compressors.   Both work with our system in normal operation but the firmware inside these units does change which can affect the testing.  We used to advise a hardwired compressor test where BLACK was grounded and RED, GREEN and ORANGE could be connected to 12V to force the compressor ON.  However, this test no longer works for recent compressors as the internal firmware has changed (nothing to do with the firmware in our ECU).

We now use two suppliers for compressors. when contacting us for support, please say which type you have:



At the time of writing the Pusong compressor does not have the 30 second restart delay, so should start immediately from a CMP=50 command.






At the time of writing the Beling compressor does not have the 30 second restart delay, so should start immediately from a CMP=50 command.  Earlier Benling compressors do have the 30 second restart delay timer.








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We have had occasional issues with the crimp sockets inside the ecu socket not gripping the pin, resulting in an intermittent connection of compressor drive.

A simple test is to see whether the socket will grip the leg of a standard resistor.  Push the resistor leg into each socket and it should grip it - if it falls out easily then this could lead to odd behaviour like compressor stopping 'at random' or not starting.  



Unfortunately it is not easy to fix the crimp socket receptacle.  We have raised this issue with our wiring contractor and it may be due to a batch error with the crimp.

Our suggested workaround is to add some solder to the mating pin (compressor side) to make the pin a bit fatter.

If you still have issues then the plug and socket can be replaced with an alternative ( such as Deutsch DTM series )


Wire colours connections from ECU to Compressor:














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