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Ramantanis Dimitris

Tachometer

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Another question is: The oem ac computer receives the same signal as tacho in order to see that engine runs and activate the compressor clutch. With this modification the ac ecu does not activate the clutch. Is there any possibily the current isnt enough strong to trigger the ac computer? fingers crossed...

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No there no resistor in the relay. I simply done the schem above but with 0.33 kohm resistor. Is it safe for the ecu?Shall I use a diode at the ecu output signal?

The ECU will be ok with no resistor or diode.

Another question is: The oem ac computer receives the same signal as tacho in order to see that engine runs and activate the compressor clutch. With this modification the ac ecu does not activate the clutch. Is there any possibily the current isnt enough strong to trigger the ac computer? fingers crossed...

This is possibly what is happening. The relay may be pulling down the amplitude of the tacho output. You would want to examine the signal with an oscilloscope to know for sure.

Scott

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Another simplethings that works 100% is to use the oem's coil primary terminals. The connection is simple. + coil terminal connected to an IG+, - coil terminal connected to tachometer cable (as it was when OEM ecu was used) and tacho output from ecu connected to the coils edge - with a 0.33 kohm resistor. Same like the image that AdamW posted but in case of the relay coil we use the oem's coil primary terminals. Work 100% and also triggers the A/C OEM computer.

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Another simplethings that works 100% is to use the oem's coil primary terminals. The connection is simple. + coil terminal connected to an IG+, - coil terminal connected to tachometer cable (as it was when OEM ecu was used) and tacho output from ecu connected to the coils edge - with a 0.33 kohm resistor.

Edited my original post here since I had misread the resistor as 0.33ohm, not 0.33kohm which will limit current.  Still not sure I like this idea...

Edited by Adamw
incorrect comments made

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