Hello all,

I installed a 12v AC compressor, it's working fairly well. My factory AC wiring is removed. I currently have 2 fans that turn on when the coolant temp reaches the trigger temp set on the MS. My question is can I use a single relay to do two functions? 1) to turn the fans on when the coolant reaches temp 2) turn fans on when AC is turned on.

Will the 12v signal wire from the AC fan control cause damage if I wire the signal wire both the coolant and ac signal together?

Will it some how back feed into the ECU and burn it out if I wire 2 signal wires? I want to basically just add a switch to turn the AC on. Or do I need another relay just for the AC. I want to stay away from wiring anything to the ecu because my stock AC wiring is damaged and missing some parts.

 

Typically you use 2 outputs from an ECU for AC, one for aux fan, one for compressor. That way you can turn the aux fan on for either extra cooling, or if the AC is on. These outputs are typically ground outputs, going to terminal 85 or 86 of a relay, with the other 85/86 terminal getting 12v, which you can jump from the relay’s main feed at terminal 30.

 

thank you for the reply. Essentially I am asking if I feed a 12v signal back up through the fan signal wire that goes to the ECU will that short it out? basically both signal wires will be connected I definitely need both fans going to cool the condenser.

I am asking a relay to do 2 jobs instead of one. 1) turn on when the coolant temp threshold is met 2) turn on when AC compressor is turned on.

Is it best to have another relay set up?

 

Short answer is yes, it'll short it out. The "signal" wire, is a ground output, so feeding it 12v is bad. Some outputs are capable of running high side, I'm unsure which ones can do that on your particular ECU. But if you take 2 outputs from your ECU and feed them both to one relay, it'll work. Sadly you can't (as far as I know) share outputs in TS, but they need to both be ground outputs.

I can't quite tell if you're asking about controlling the compressor clutch and fan with one relay, or asking if you can control the aux fan with two outputs.

 

I bought a 12v ac compressor kit on Amazon it's not belt driven I don't have the space to run my belt driven compressor due to the turbo pipes. The compressor is in my trunk now, if running one relay with two input sources is bad the only fix is another relay mimicking the original set up. This way the ecu can control the engine cooling fan and the other relay controlling fans when AC compressor is turned on. I was hoping I can just wire it up directly but I wanted to make sure it was safe. Would totally suck destroying the ECU over a simple thing.