Stock Cooling Fans
TECH Apprentice
Joined: Oct 2010
Posts: 341
Likes: 18
From: Colorado
From my understanding, they use three relays because the fans run at a low speed (initial on) and high speed (full temp or with A/C) and I think that they draw too much amperage on high for only two relays to handle... From messing around with my LT1 swap in my truck, I think that they use two relays for low and the third relay is used for high speed to handle the extra amp draw. I never found an actual wiring diagram to pin down how exacting the relays are wired, but if you pull one relay while the fans are on high, one will switch to low... Im also guessing it is for safety, in the case that one relay fails,you still have cooling from the fan(s) at some level... just my observations, may not be 100% correct.
it's about the simplest way with the least amount of parts and least expensive/common parts to give the functionality of both fans on low speed and both fans on high speed with two control wires going to the pcm. The pcm grounds one wire and activates the relays such that the fan motors operate in series, so they see half the current and run at low speed. when the pcm grounds both control wires from the relays the fan motors operate in parallel and run at high speed. A side effect of this setup is if you only put one control wire to ground and it's the other one, then just one radiator fan runs at high speed and the other one gets no power and does not run.
I've seen the wiring diagram in my service manual and it is somewhat ingenious. you might be able to google it and find the diagram online.
fyi if any of the relays fail then you will not get full operation of your fans, depending on which relay fails. having 3 relays is not for safety, and any one relay can power both fans. they are rated well above what the fan motors draw. having 3 just lets you control the fans like i mentioned, with common electronic parts.
I've seen the wiring diagram in my service manual and it is somewhat ingenious. you might be able to google it and find the diagram online.
fyi if any of the relays fail then you will not get full operation of your fans, depending on which relay fails. having 3 relays is not for safety, and any one relay can power both fans. they are rated well above what the fan motors draw. having 3 just lets you control the fans like i mentioned, with common electronic parts.
https://ls1tech.com/forums/conversio...ls1-fox-2.html
this thread post #36 has the fan wiring diagram, "First heres the diagram to wire up the camaro dual fans. This diagram is for the fans to be dual speed."
at the pcm there's dk gn wire pin 42, when just that is grounded fans run in series electrically and at low speed. When both pin 42 and pin 33 dk blu wire are grounded relays make the fans run in parallel at high speed.
also, not all 3 relays are the same. The 2 relays on the outside of the diagram are a simple on/off relay (SPST - single pole single throw). the center relay is a SPDT (single pole double throw) relay.
this thread post #36 has the fan wiring diagram, "First heres the diagram to wire up the camaro dual fans. This diagram is for the fans to be dual speed."
at the pcm there's dk gn wire pin 42, when just that is grounded fans run in series electrically and at low speed. When both pin 42 and pin 33 dk blu wire are grounded relays make the fans run in parallel at high speed.
also, not all 3 relays are the same. The 2 relays on the outside of the diagram are a simple on/off relay (SPST - single pole single throw). the center relay is a SPDT (single pole double throw) relay.
Joined: Nov 2003
Posts: 11,329
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
Excellent explanation! Just one small correction... the fans running in series each get half the voltage - current in a series circuit remains constant.
Thanks everybody. First time I've been in here since I first posted.
I found a wiring diagram and was alittle confused at first. Finally figured out that they do run in series and then in parallel.
Also played with the PCM wires, and saw what each wire does. I'm rewiring my car.
It's a track only car. I'm going to put in a aux switch, to turn the fans on manually.
Still let the PCM turn them on, but manually turn then on in the pits in between rounds.
Again thanks!
I found a wiring diagram and was alittle confused at first. Finally figured out that they do run in series and then in parallel.
Also played with the PCM wires, and saw what each wire does. I'm rewiring my car.
It's a track only car. I'm going to put in a aux switch, to turn the fans on manually.
Still let the PCM turn them on, but manually turn then on in the pits in between rounds.
Again thanks!
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Another question.
Which fans do I need to manually turn on in the pits and staging lanes to keep car cooler.
Both fans on low, both fans on high or single fan on high?
Which fans do I need to manually turn on in the pits and staging lanes to keep car cooler.
Both fans on low, both fans on high or single fan on high?
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My advice, buy a fan to put in front of the car. I've done the track only car....sold it not too long ago. :o( It'd only be a matter of time before you forget about it....and it won't take long for them to kill your battery.
Staging Lane
Joined: Nov 2011
Posts: 73
Likes: 0
Somewhat related question: My fans will NOT kick on at all, and I've replaced all three relays and temp sensors. I currently have the main relay hotwired so the fan runs constantly. It's gotta be a PCM issue, right?
93 TA M6, CC stage 3 clutch, freshly built trans, AC delete, CAI
93 TA M6, CC stage 3 clutch, freshly built trans, AC delete, CAI
Joined: Nov 2003
Posts: 11,329
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
Somewhat related question: My fans will NOT kick on at all, and I've replaced all three relays and temp sensors. I currently have the main relay hotwired so the fan runs constantly. It's gotta be a PCM issue, right?
93 TA M6, CC stage 3 clutch, freshly built trans, AC delete, CAI
93 TA M6, CC stage 3 clutch, freshly built trans, AC delete, CAI
out of my 2002 service manual (don't know if it applies to a 1993) the electric fans don't get turned on low speed by the pcm until coolant temp is 226F and on high speed until 234F.
The electric fans are controlled by the PCM. one relay is grounded by the pcm for low speed, or two relays get grounded for high speed. When the AC is turned on, the PCM knows high refrigerant pressure via a sensor and when it's over so many kPa it turns the fans on low speed or high speed just like it does with coolant. I know whenever you drop below 30mph too with the AC or defog on the PCM commands the fans on.
for staging you'd want to ground both wires to make both fans on high speed.
with the fans on high speed you will know when you turn the car off so it's very hard to not notice and forget. Leaving them on low speed is a different story. I've manually switched mine on low speed then forget when I got to work. Low speed fans ran from 9am to 4pm. Car started, but obviously don't take that as a guarantee you can leave your fans on low speed for 8 hrs and not have a problem. If you're battery is decent, low speed engine off for 1-2 hours should not hurt the battery.
if you're electric fans to never seem to turn on while you are diagnosing, it may be because you're coolant temp is not hot enough. I'm pretty sure however they will always turn on low speed when the AC is turned on and you are parked. You should do that then probe the 2 radiator fan wires from the PCM to the relays and make sure just the one which does low speed has continuity to ground. Check the link above for the pin # and wire color for the low speed, I don't remember.
The electric fans are controlled by the PCM. one relay is grounded by the pcm for low speed, or two relays get grounded for high speed. When the AC is turned on, the PCM knows high refrigerant pressure via a sensor and when it's over so many kPa it turns the fans on low speed or high speed just like it does with coolant. I know whenever you drop below 30mph too with the AC or defog on the PCM commands the fans on.
for staging you'd want to ground both wires to make both fans on high speed.
with the fans on high speed you will know when you turn the car off so it's very hard to not notice and forget. Leaving them on low speed is a different story. I've manually switched mine on low speed then forget when I got to work. Low speed fans ran from 9am to 4pm. Car started, but obviously don't take that as a guarantee you can leave your fans on low speed for 8 hrs and not have a problem. If you're battery is decent, low speed engine off for 1-2 hours should not hurt the battery.
if you're electric fans to never seem to turn on while you are diagnosing, it may be because you're coolant temp is not hot enough. I'm pretty sure however they will always turn on low speed when the AC is turned on and you are parked. You should do that then probe the 2 radiator fan wires from the PCM to the relays and make sure just the one which does low speed has continuity to ground. Check the link above for the pin # and wire color for the low speed, I don't remember.
I put both fans on high with my manual override switch.
I bought a DPDT switch, put the fan relay controls on the common terminals, the PCM wires on one side and a grounded wire(s) on the other side. That way I can leave the switch in the down position and let the PCM control them and override them in the top position. Also wired a indicator light to the fan wire after the relay, so I can tell when the fans are on.
Thanks everyone for the info.
I bought a DPDT switch, put the fan relay controls on the common terminals, the PCM wires on one side and a grounded wire(s) on the other side. That way I can leave the switch in the down position and let the PCM control them and override them in the top position. Also wired a indicator light to the fan wire after the relay, so I can tell when the fans are on.
Thanks everyone for the info.
I put both fans on high with my manual override switch.
I bought a DPDT switch, put the fan relay controls on the common terminals, the PCM wires on one side and a grounded wire(s) on the other side. That way I can leave the switch in the down position and let the PCM control them and override them in the top position. Also wired a indicator light to the fan wire after the relay, so I can tell when the fans are on.
Thanks everyone for the info.
I bought a DPDT switch, put the fan relay controls on the common terminals, the PCM wires on one side and a grounded wire(s) on the other side. That way I can leave the switch in the down position and let the PCM control them and override them in the top position. Also wired a indicator light to the fan wire after the relay, so I can tell when the fans are on.
Thanks everyone for the info.
