Fan Relay Control

[Josh]

So I am just finishing up my wiring harness and I am second guessing my fan relay wiring. I have opted to do a MS controlled circuit dependent on coolant temp and eliminating the otterstat. However, I also want the fans to engage when the A/C clutch is engaged. So this confuses me. I know you can switch a relay using IAC1A and IAC1B (same goes with the IAC2 ports) and they are inverse to one another (one 12V one ground). But the A/C clutch outputs 12V so to prevent going to a double thrown relay I was wondering if I could just use a chassis ground and power the relay with just IAC1A (configured accordingly as a 12V output), or since IAC1B is not used no current can be output? I have attached a schematic for clarity, just wondering if the proposed idea will work. FYI I am using a 2 wire IAC so i am controlling it with the FIDLE circuit.

[Bitsyncmaster]

So I am just finishing up my wiring harness and I am second guessing my fan relay wiring. I have opted to do a MS controlled circuit dependent on coolant temp and eliminating the otterstat. However, I also want the fans to engage when the A/C clutch is engaged. So this confuses me. I know you can switch a relay using IAC1A and IAC1B (same goes with the IAC2 ports) and they are inverse to one another (one 12V one ground). But the A/C clutch outputs 12V so to prevent going to a double thrown relay I was wondering if I could just use a chassis ground and power the relay with just IAC1A (configured accordingly as a 12V output), or since IAC1B is not used no current can be output? I have attached a schematic for clarity, just wondering if the proposed idea will work. FYI I am using a 2 wire IAC so i am controlling it with the FIDLE circuit.

Yes that should work. That is pretty much what the OEM harness did.

[Josh]

Thanks for the input Dave. Just glad to get rid of the cobbled together OEM setup!

[dn010]

What diodes & relay did you use for this circuit?

[Josh]

nothing special. just a standard 30/40 relay and a basic 1N4001 diode. Been running this circuit for a few seasons now, no issues.

[Bitsyncmaster]

What diodes & relay did you use for this circuit?

You would probably use the normal fan relay (30 or 40 amp rated). The diode can be a one amp but you want about 200 volts rating when it's switching inductive loads like the relay coil.

[dn010]

Thanks Dave & Josh!

You would probably use the normal fan relay (30 or 40 amp rated). The diode can be a one amp but you want about 200 volts rating when it's switching inductive loads like the relay coil.

[FABombjoy]

Since the threading matched, I have mine in the return Y pipe in place of the vacuum switch. Seemed like a decent place to get an accurate read.

If it fits tho, I might move the sensor to the water pump as I'm considering putting my turbo water return and oil heat exchanger returns into the Y pipe instead. Right now it's an untidy H pipe into the heater return hose, but I could install fitting in place of the kjet sensors and run the hoses that way.

The Y pipe is a return, right? Am I looking at the flow path correctly? Coolant flows up, out the mini hoses into the heads (and tstat once open) and then returns from the Y pipe and heater hard pipe?

[dn010]

Since the threading matched, I have mine in the return Y pipe in place of the vacuum switch. Seemed like a decent place to get an accurate read.

If it fits tho, I might move the sensor to the water pump as I'm considering putting my turbo water return and oil heat exchanger returns into the Y pipe instead. Right now it's an untidy H pipe into the heater return hose, but I could install fitting in place of the kjet sensors and run the hoses that way.

The Y pipe is a return, right? Am I looking at the flow path correctly? Coolant flows up, out the mini hoses into the heads (and tstat once open) and then returns from the Y pipe and heater hard pipe?

I used the water pump location because that is where the sensor was originally on the B280F. Didn't feel like messing around with more work when a swap is already enough work and wiring, etc.

Attached are coolant routes, one is the B28F, the other the 3.0 and they're pretty much both the same (heater core and expansion tank differences). B280F engine that I'm using has the oil heat exchanger lines running #1 from the block & #2 a line running to the the steel "return" pipe (stock D's engine steel return pipe is different with only one enter/exit passage). If you need sensor information or resistor values I have them depending on which sensor you're using.





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[FABombjoy]

Thanks for posting that! I'd seen it months ago but could not find it again.

So the Y pipe for supply and not for return, so much for my hypothesis

Looks like I will put together a better solution for the turbo & exchanger return lines.