Jaivus Posted June 18, 2021 Report Share Posted June 18, 2021 Hello there, I have a problem where the A/C only works on fan speed 1. On fan speed 2, 3 and 4 I believe the a/c clutch does not turn on and it only blows warm air on a hot day. I noticed that the A/C Request only activates on the first speed. Since the ECU software does not let you set a voltage activation threshold does anybody know the voltage required to activate the A/C Request? For background I had the system recharged recently, maybe a month ago and I had taken the car to check out the wiring and switches on the console and everything seems to work fine from what I was told. I think it's safe to assume that I have some issue getting a proper signal to/from the ECU as the a/c had worked with the stock ECU in place. Please let me know if you have any insight into this problem Thanks! Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 18, 2021 Report Share Posted June 18, 2021 I have definitely seen this before on an FD. On the odd one the user has had to add a diode inline to drop the voltage a bit. Can you tell us the voltage on the AC request pin in the 4 fan speeds. Should be pin 4V if its a S7/8 ecu. You can back probe with something like a pin or paper clip into the wire side of the connector. Jaivus 1 Quote Link to comment Share on other sites More sharing options...
Jaivus Posted June 20, 2021 Author Report Share Posted June 20, 2021 Hey, taking measurements of the A/C request from pin 4V I have the following voltages FAN 1: 2.15V FAN 2: 2.8V FAN 3: 3.05V FAN 4: 2.9V Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 20, 2021 Report Share Posted June 20, 2021 Ok, that is a little higher than the AC circuit on that ECU was designed for. We have 2 diodes in series on that pin before it goes to the DI, so they will reduce those reported voltages by about 1.4V. So in fan speed 3 there will still be about 1.65V getting through to the DI. The voltage on the DI needs to drop below about 1.0V to activate the DI. So the quickest solution would be to add another 2 diodes inline into that AC request wire. Something common like 1n4148, with the stripe pointing towards the ECU. Quote Link to comment Share on other sites More sharing options...
Jaivus Posted June 20, 2021 Author Report Share Posted June 20, 2021 Thanks, that sounds like something that I could try. I have a bunch of 1N4007 diodes on hand, would those work as well? Otherwise I'll try it with the 1N4148 and see how it goes Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 20, 2021 Report Share Posted June 20, 2021 Give them a try, they wont drop the voltage quite as much but probably enough. Quote Link to comment Share on other sites More sharing options...
Cjmoveen Posted November 17, 2021 Report Share Posted November 17, 2021 On 6/20/2021 at 2:00 PM, Adamw said: Ok, that is a little higher than the AC circuit on that ECU was designed for. We have 2 diodes in series on that pin before it goes to the DI, so they will reduce those reported voltages by about 1.4V. So in fan speed 3 there will still be about 1.65V getting through to the DI. The voltage on the DI needs to drop below about 1.0V to activate the DI. So the quickest solution would be to add another 2 diodes inline into that AC request wire. Something common like 1n4148, with the stripe pointing towards the ECU. i have this same issue on a s6 ecu should i do the same ? i see the ac request turning on for a second and going back off Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 17, 2021 Report Share Posted November 17, 2021 Yeah, can you check those voltages as suggested above to confirm first. Quote Link to comment Share on other sites More sharing options...
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