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!

[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]

What diodes & relay did you use for this circuit?

[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.

[dn010]

One last question, I promise!

I was looking at everything last night trying to find the easiest way to do this - the schematic shows that the existing AC & otterstat wiring already have diodes installed so provided they are still there I would leave that alone. So, it seems to me if I hook the otterstat black/orange wire to my MS3X Nitrous switched +12VDC (of course programmed to fan control in TS), could I not just install a 30/40 replay in the blue socket and call it a day? I'd clip the fan fail warning light Black/orange wire and splice it into the NO2 / black/orange wire so the light would come on when fans are tripped. I am using DPI fans so the amp draw should be much less for the relay & related wiring to handle.

Basically, I am curious if I need to worry about socketing a replay in place of the splice wires in the blue fan fail socket, or should I just take out the blue socket and wire up 2 more relays to control each fan.

Thanks in advance,
Dan B.

[Bitsyncmaster]

The fan fail socket is not configured (pin connections) for any standard relay. Are you leaving the OEM fan relay installed? It sounds like all you need to do is cut the wire that was coming from the otterstat and use that wire to connect to your ECU. You would leave the stock diodes connected so when the AC is on it would run the fans or when the ECU wants to run the fans.

[dn010]

Thanks for your reply Dave, I'm glad I asked first! I do have the otterstat wire already cut and running to my MS, it is just a matter of splicing it with the NO2 switched wire and configuring it. I am looking at the cooling fan circuit diagram and see now that the socket isn't in proper configuration, I should have studied it before asking. I do plan to leave the OEM fan relay installed since it will be getting the same +12VDC as it was originally but from a different source. So unless I get one of your SS relays or I build 2 relays to control each fan, I'm stuck using the ugly burnt splice wires for now.

Thanks again!

[Bitsyncmaster]

You would need 12 volts or better a little higher that can drive about 60 to 80 ma. to turn the fan relay on by just spicing into that otterstat wire. Not sure is your "NO2" circuit can drive that.

[dn010]

Turns out I couldn't use the N2O wire I wanted as it was only an "IN" and could not be used for voltage out. So, I used a sequential injector wire from the ECU to wire up a relay using the injector wire as a ground to make the relay function, sending +12VDC to the original fan relay and then the splice wire (fan fail) etc.

I was trying to get away with not having to use yet another relay but I couldn't in the end. At least I have functioning fans now! Thanks again guys.

[dn010]

Sorry to resurrect this yet again but when you ran this circuit, did you have any power issues once you shut off the AC? If the compressor is engaged and I turn the mode switch to off, my battery light comes on for a moment and then turns off. Now that I have a clock installed, it will also reset the clock from whatever time to 12:00. This is starting to become somewhat of annoyance and I can't seem to figure out where this is coming from. I have a diode at the compressor. It's only when I turn the switch off, if the AC is cycling it does not give me any issues, same with the fan - the fans can cycle no problems.

[Bitsyncmaster]

Sorry to resurrect this yet again but when you ran this circuit, did you have any power issues once you shut off the AC? If the compressor is engaged and I turn the mode switch to off, my battery light comes on for a moment and then turns off. Now that I have a clock installed, it will also reset the clock from whatever time to 12:00. This is starting to become somewhat of annoyance and I can't seem to figure out where this is coming from. I have a diode at the compressor. It's only when I turn the switch off, if the AC is cycling it does not give me any issues, same with the fan - the fans can cycle no problems.

I had a reset on my electronic battery relay when I turned the AC off but the zener diode on the compressor fixed that. A diode should also work. I would suggest you test that your diode is still working.

The compressor clutch turning off puts out a negative 200 volt spike which probably gets into the grounds of the car.

[dn010]

Thank you. I will check that it is still operational. I never removed the factory diode so even if it isn't working, that diode should still be there. My confusion here is the clutch cycling on and off does not cause any abnormalities, it is only when I use the mode switch from any AC mode to off that creates this issue. If the diode was bad, wouldn't this happen when the clutch cycles too? I'll check the diode tonight along with some other things, I now wonder if I unhook the compressor and try the mode switch, if it would still create this problem.



I had a reset on my electronic battery relay when I turned the AC off but the zener diode on the compressor fixed that. A diode should also work. I would suggest you test that your diode is still working.

The compressor clutch turning off puts out a negative 200 volt spike which probably gets into the grounds of the car.

[FABombjoy]

The factory diode keeps the otterstat from turning the ac compressor on. Diodes almost always fail open circuit, so if the factory diode was bad your fans would not turn on with the AC. If it failed short your compressor would have a mind of its own.

The schematic shows a noise suppression capacitor on the mode switch that might be defective or disconnected from ground.

[dn010]

Problem is, my setup is using a MS ecu, engine swap, etc. so I'm not even sure without looking at my car's specific wiring diagram I made, what changes I made or what I bypassed. I do know for sure I wired in a diode, in the wire going to the compressor. Interestingly, my radio hasn't worked for a while, no power, so maybe it is something going on behind the plate that needs attention. Just when you think you're all done with one area of the car....


The factory diode keeps the otterstat from turning the ac compressor on. Diodes almost always fail open circuit, so if the factory diode was bad your fans would not turn on with the AC. If it failed short your compressor would have a mind of its own.

The schematic shows a noise suppression capacitor on the mode switch that might be defective or disconnected from ground.

[Bitsyncmaster]

Thank you. I will check that it is still operational. I never removed the factory diode so even if it isn't working, that diode should still be there. My confusion here is the clutch cycling on and off does not cause any abnormalities, it is only when I use the mode switch from any AC mode to off that creates this issue. If the diode was bad, wouldn't this happen when the clutch cycles too? I'll check the diode tonight along with some other things, I now wonder if I unhook the compressor and try the mode switch, if it would still create this problem.

I mistook your diode comment to think you installed a suppressor that I recommended in a thread.

http://dmctalk.org/showthread.php?12203-Electrical-noise-fix-for-AC-compressor-clutch

If you don't have that diode or zener I can 90% say that will fix your problem.

Using the switch brings that voltage spike up to the center console. Normal AC the switching happens at the low pressure switch.

[dn010]

Excellent read, thank you for posting this. I will see if I have the zener among my electrical components and if not I'll order it & install. Thank you again!


I mistook your diode comment to think you installed a suppressor that I recommended in a thread.

http://dmctalk.org/showthread.php?12203-Electrical-noise-fix-for-AC-compressor-clutch

If you don't have that diode or zener I can 90% say that will fix your problem.

Using the switch brings that voltage spike up to the center console. Normal AC the switching happens at the low pressure switch.

[dn010]

Received the correct Zener diodes yesterday, I have a ton of them but not the number you posted. Installed it today and the problem disappeared! Thank you again for posting that Dave, one less frustration now. I am on to heat shrink wrapping the install now, always something to do. By the way, I haven't forgotten about ordering your dimmer relay, just need to figure out the rest of my alarm removal situation first, one of these days I'll be done.

thanks again - Dan B.

[FABombjoy]

Since this thread is getting some more attention... :D

For those using MS to control the cooling fans, any recommended settings for on/off temps? I have my temp sensor in the Y pipe but the otterstat is far enough downstream that it seems like slightly hotter temp points would be called for.

[Bitsyncmaster]

Received the correct Zener diodes yesterday, I have a ton of them but not the number you posted. Installed it today and the problem disappeared! Thank you again for posting that Dave, one less frustration now. I am on to heat shrink wrapping the install now, always something to do. By the way, I haven't forgotten about ordering your dimmer relay, just need to figure out the rest of my alarm removal situation first, one of these days I'll be done.

thanks again - Dan B.

Glad it fixed it. The part number you use is not that critical. The part just needs to clamp that inductive spike.

[Bitsyncmaster]

Since this thread is getting some more attention... :D

For those using MS to control the cooling fans, any recommended settings for on/off temps? I have my temp sensor in the Y pipe but the otterstat is far enough downstream that it seems like slightly hotter temp points would be called for.

I'm planning on doing some testing soon. I plan to install my "solid state otterstat" in the coolant return line going to the water pump and I will stick a thermal sensor (reads out on my multimeter) in there also. First test will keep the OEM otterstat controlling the fans to just see what the return line does.

Still not sure why the otterstat is in the feed line to the radiator.

[dn010]

Since this thread is getting some more attention... :D

For those using MS to control the cooling fans, any recommended settings for on/off temps? I have my temp sensor in the Y pipe but the otterstat is far enough downstream that it seems like slightly hotter temp points would be called for.

I am running off of the temp sensor located in the head, rear passenger side, I was able to find a good value table for this sensor which gives the ECU pretty accurate temp readings. I can look during my lunch hour to verify, but I am 99.9% sure I have it set to the stock 190 on 210 off setting.

EDIT: Actually I am already wrong. The sensor in the head I have running to my gauge. I'm using the sensor in the water pump (pump and sensor is from a 1987 Volvo 780) to feed the temp to my ECU. The sensor I am sure can be installed in the stock D pump.

[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.





51005
51006

[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 :D

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