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Question is; Where is the sensor that controls when my electric fan turns on?
More background info here; My fan decided to quit running on about the hottest day of the year, causing my cooling system to get too hot, and my radiator to crack (wonderful, I know).
My issue is not with replacing the radiator (although aggravating that my cap didn't release the pressure, but stuff happens I guess). It is more with deciphering the misinformation from various sources, and self inflicted confusion on what actually turns the fan on.
Basically, to my knowledge, there is a temperature sensor behind the alternator and underneath the induction. As much as I want my problem to be with this sensor (as it would be infinitely easier to replace), after reading in forums, it appears that it may actually be a "temperature switch" located in the passenger side head, between plugs 6&8 (looks like I have to remove the dipstick in order to gain access to it?). More confusion is had when I read somewhere that the computer actually controls the fan, and the switch is just a fail safe.
Anyway, I am just looking for clarification before I remove and replace what looks to be a PITA to access. Any information would be appreciated. Thanks!
Question is; Where is the sensor that controls when my electric fan turns on?
More background info here; My fan decided to quit running on about the hottest day of the year, causing my cooling system to get too hot, and my radiator to crack (wonderful, I know).
My issue is not with replacing the radiator (although aggravating that my cap didn't release the pressure, but stuff happens I guess). It is more with deciphering the misinformation from various sources, and self inflicted confusion on what actually turns the fan on.
Basically, to my knowledge, there is a temperature sensor behind the alternator and underneath the induction. As much as I want my problem to be with this sensor (as it would be infinitely easier to replace), after reading in forums, it appears that it may actually be a "temperature switch" located in the passenger side head, between plugs 6&8 (looks like I have to remove the dipstick in order to gain access to it?). More confusion is had when I read somewhere that the computer actually controls the fan, and the switch is just a fail safe.
Anyway, I am just looking for clarification before I remove and replace what looks to be a PITA to access. Any information would be appreciated. Thanks!
(fan and relay are functional)
Welcome to TGO!!
By your post, I'll assume you have a single fan set up.
In a single fan set up, the ECM does not control the fan, only the fan "switch" controls the fan, unless you turn on the AC which overrides the switch.
There are three main components of the fan system. The Fan, the Fan relay, and the Fan switch.
So, first question, since the system is still all connected, does your fan turn on when you turn on the AC?
If it does, then the "circuit" is good and you don't have to worry about your inline-fuse being bad.
You say the fan is good, so you have run power to it directly to ensure it spins when power is applied? If the fan does not spin after turning your AC on, disconnect your fan and run power strait to it from the battery. Does the fan physically spin with power direct from the battery (I just run wire from the positive and negative leads on the battery to the terminals on the fan motor).
If the fan turns on with the AC, then your next step is to pull the wire off of the fan switch on the passenger side. Many times this wire is cut/melted/broken and is the culprit. If the wire is intact, pull the connector off and ground the wire with the car in the "run" position.
The fan switch activates by sending a ground signal to the relay which energizes and turns the fan on. By grounding the connector to chassis ground or the like, you'll create a similar situation. If the fan turns on by doing this, then you confirm the the wiring and Relay is good and the culprit is the switch on the head. If the fan does not turn on, most likely the relay is bad. If the fan does not turn on, reconnect the wire to the switch.
The fan switch is located below your exhaust manifold on the passenger side just forward of the dip-stick. With headers, I can reach mine from the top of the car. If you're running the factory manifolds, your best bet may be going up from the bottom.
The relay is a 4-wire relay located up near the brake booster and faces forward. If you do a search here I'm certain you'll find a photo of it. How did you verify the relay was good? I'm going to cover how to check it anyway.
Once disconnected, take the connector and short the two fat leads, should be the two outer wires, together. This takes power and puts it from one side fo the connecto strait to the fan simulating the relay activation. If the fan turns on, your relay is bad.
Alternately, the pins on the connector may have come a little loose and are not making good contact with the relay. Reconnect the relay and re-seat all the wires by pushing up on them hard to make sure they are seated all the way.
Hey guys, thanks for the response(s). I do have dual electric fans, and I have my compressor belt removed (so no A/C). I think I found what I need in the "Think your fans aren't working" thread. Quoted below;
"... The passenger fan will turn on at the stock "fan switch" temp (found in passenger side head between spark plugs #6 and #8). The stock fan switch is 235°F. It will also turn on when the air conditioning high-side pressure is above 233 psi. It will shut off around 190 psi."
And then a little later- "1987 cars with dual electric fans have a slight difference in that turning on the A/C won't turn on the passenger fan. It is only controlled by the coolant temperature in relation to the "fan switch." So if your car has 220°F coolant and the A/C is on, your passenger fan will be off......I suspect this was a one year only deal because GM figured out that the air conditioning worked better on dual fan cars if the A/C could control when the passenger fan turned on. I live in Texas and even during the peak of summertime hell, the car very rarely ever hits 235° coolant temps. But I need every bit of help I can get in terms of air conditioning performance. (My car is a 1989. I'm lucky in this regard.)"
So, with that in mind... Any suggestions on gaining access to it? I feel like I need a rubber arm to get to the switch in the first place =/... It feels like (notice how I say feel, because I can't actually see it) I need to remove the dipstick, because it is right in the way. After removing the dipstick, I could maybe get in there with a Mr. Twisty...
Last edited by Colt-87TransAm; 09-19-2013 at 01:23 PM.
Oh, and thanks Ozz for such a detailed response! Your time is greatly appreciated!
Again, I do have dual fans. I ran power direct to the fans and they turn on. Unfortunately, it seems that 87 does not turn the driver fan on w/ just the A/C on. Additionally, I am not positive it would work for me, as I have my compressor belt removed.
The relay is good, as I can run power to it and watch it close. Although, I have not entirely ruled out any of the connector(s) in the system. They all look like garbage...
The below quote is very helpful! I suspected that was how it functioned, but I wasn't positive. I will try grounding the wire tonight when I get home and see what happens.
Originally Posted by Ozz1967
The fan switch activates by sending a ground signal to the relay which energizes and turns the fan on. By grounding the connector to chassis ground or the like, you'll create a similar situation. If the fan turns on by doing this, then you confirm the the wiring and Relay is good and the culprit is the switch on the head. If the fan does not turn on, most likely the relay is bad. If the fan does not turn on, reconnect the wire to the switch.
The fan switch is located below your exhaust manifold on the passenger side just forward of the dip-stick. With headers, I can reach mine from the top of the car. If you're running the factory manifolds, your best bet may be going up from the bottom.
Oh, and thanks Ozz for such a detailed response! Your time is greatly appreciated!
Again, I do have dual fans. I ran power direct to the fans and they turn on. Unfortunately, it seems that 87 does not turn the driver fan on w/ just the A/C on. Additionally, I am not positive it would work for me, as I have my compressor belt removed.
The relay is good, as I can run power to it and watch it close. Although, I have not entirely ruled out any of the connector(s) in the system. They all look like garbage...
The below quote is very helpful! I suspected that was how it functioned, but I wasn't positive. I will try grounding the wire tonight when I get home and see what happens.
Thanks again Ozz!
Glad to help out.
Since you have dual fans, the ECM turns the primary fan on at 225*, the fan switch will turn the second fan on at 235*. Both fans should turn on with the AC, so that's telling me you have more of an issue.
Also, even though the compressor belt is removed, if you have your compressor hooked up, it will "energize the circuit" even if your AC ciompressor won't turn.
So on a one fan 2.8l the fan only turns on at 235 degrees??
Originally Posted by Colt-87TransAm
Hey guys, thanks for the response(s). I do have dual electric fans, and I have my compressor belt removed (so no A/C). I think I found what I need in the "Think your fans aren't working" thread. Quoted below;
"... The passenger fan will turn on at the stock "fan switch" temp (found in passenger side head between spark plugs #6 and #8). The stock fan switch is 235°F. It will also turn on when the air conditioning high-side pressure is above 233 psi. It will shut off around 190 psi."
And then a little later- "1987 cars with dual electric fans have a slight difference in that turning on the A/C won't turn on the passenger fan. It is only controlled by the coolant temperature in relation to the "fan switch." So if your car has 220°F coolant and the A/C is on, your passenger fan will be off......I suspect this was a one year only deal because GM figured out that the air conditioning worked better on dual fan cars if the A/C could control when the passenger fan turned on. I live in Texas and even during the peak of summertime hell, the car very rarely ever hits 235° coolant temps. But I need every bit of help I can get in terms of air conditioning performance. (My car is a 1989. I'm lucky in this regard.)"
So, with that in mind... Any suggestions on gaining access to it? I feel like I need a rubber arm to get to the switch in the first place =/... It feels like (notice how I say feel, because I can't actually see it) I need to remove the dipstick, because it is right in the way. After removing the dipstick, I could maybe get in there with a Mr. Twisty...
I too have an issue with the connector for the fan switch its gone. I can buy one but where does it connect? My fan is always on when key is on.
If it's always on when the car is on, it's grounded on something or it's been wired that way previously. Look for a loose wire hanging down in that area. I believe it was purple in my 84 before I went with my LS swap.
Hi and Happy New Year everybody,
I recently bought a 92 RS Camaro 305 TBI and trying to fix all the wiring mess from previous owners. I read a lot a bout the cooling system and studied wiring diagrams. I have a few questions and hopefully you guys might know the answers.
I am trying to find out the Coolant fan switch! According to everything I read its on the Passenger side between #6-#8 spark plugs. Close to the Knock Sensor. But its not! I see a plug there, its a brass one with a square tool to remove it. Also the Oil dip stick runs in front of the plug. But I found a Dark Green/white cable just hanging there! So maybe... its was there once upon a time....
I did find a sensor/switch though on the Driver side between #1- #3 Spark plugs and it has 2 prongs! But on that side I found a Dark Green cable only, which according to the diagrams goes to the Temp Gauge in the Instrument Panel!
I also have a Coolant Temp Sensor on top of the Intake manifold ( next the the water hose neck) and that one is the only one that matches the diagrams so far. Has a plug with the Yellow & Black wire.
So if I am not mistaken the switch is on the driver side and have to change it to a single prong and some how run the Green/White wire to the new switch?...
And what about that Dark Green for the Gauge, where does that go?
I would appreciate anybody help and try to attach photos.
Thanks
Nick
if like a TPI, the one on the manifold is for fan, the one on the block is for gauge. my gauge is just one connector, not two. maybe someone put wrong sensor in?
For a typical single-electric-fan car, there are 3 electric temperature things:
Coolant temp sensor - exclusively for the ECM - on the intake manifold or water outlet - yellow & black wires
Coolant temp gauge sending unit - for the temp gauge - driver's side head between #1 & #3 spark plugs - single dark green wire
Radiator fan switch - grounds the fan relay coil to turn on the relay to send power to the fan - Same hole int he head as above except on pass side (#6 & #8 plugs) - single green w/ white stripe wire
There are no temp related electric things in the block.
No idea why somebody put what looks like a CTS in that head. Maybe thought they were using it to just plug the hole? No clue. People do weird inscrutable stupid things.
Just go to the store and buy the right things and put them in the right holes. Don't try to second-guess what some yutz screwed up beforehand, just fix it.
Sounds good. Will buy a new Switch and Temp sending unit and hopefully don't run into more surprises!
Thanks a lot for the help.
And please , by all means , once you've got the previous owner's malakas straightened out , give the poor engine a new set of sparkplugs , the ones in the engine now look old enough to be legal to buy beer !
09-18-2013, 01:03 PM
Here you go.
And please , by all means , once you've got the previous owner's malakas straightened out , give the poor engine a new set of sparkplugs , the ones in the engine now look old enough to be legal to buy beer ! 
