Radator fan will not come on..

ASSISTANCE Stock Engine-Bay Components
1

will about 5 mouths ago my fan switch went out for my cooling fans.

I had replaced it with a Buddy club fan switch.

so when the car warmed up the fans would stay on all the time…

so about 3 weeks a go i notice the car was over heating and the fans did not come on.

the fan switch went bad I was thinking so I put a stock one back in but the fans still dont come on.

I know the fans work when I turn the A/C on the fans come on…

I had check the fuses they are all fine and I had change the relay now I am stuck what else can it be…

2

so BOTH fans come on w/ac on? make sure. if only the condensor fan comes on, it’s likely your rad fan motor. you can test it by running 12v straight to it. if it doesn’t come on, try running the 12v AND a separate ground. if it comes on after you apply a separate ground, you know it’s a bad ground. if not, it’s the motor

3

yes they both come on

4

ok. well then, either one of the parts you’ve replaced wasn’t good, or you have a problem in the wiring. seeing as how the path of the circuit starts at the switch, moves to the relay, then to the fan, i would start isolating by checking voltage at the relay with the car heated up to where the fan should be coming on. since it is the center of the circuit, it will guide you on which direction to go. if no voltage is present at the relay, i would test voltage at the switch. if voltage is present at the switch, the problem is between the switch and the relay. if no voltage is present at the switch, replace the switch
if you have voltage at the relay, test for voltage immediately after the relay. if voltage is not present after the relay, replace the relay. if voltage is present, the problem is between the relay and the fan

5

I know the circuit is good when I disconet the fan swich and jump it with a paper clip the fans come on withch normaly means the fan swich is bad but i change it 3 times… I going to try it again… when i cheak the circuit with my power probe everything works grr…

6

well, then. that is very strange.
only thing i can think of is that maybe the gauge is reading wrong and you aren’t actually overheating. it would make sense, seeing as how you’ve tried 3 switches.
i would check the engine temp with a temp gun and compare it to the gauges reading

edit: but then the fan should still come on if left to idle for long enough. unless it were really really cold.
i would probably still check with the gun anyways

7

I believe that those thermo sensors and switches work very poorly in the absence of water. Have you bled the coolant system since you replaced the switch? I know that is a very basic thing, but it is worth asking.

Also, welfare, the radiator fan system is ground switched so the final destination is actually the thermo switch as far as voltage goes. I’m not trying to bust your chops, it’s just that if the system is working properly and the coolant is above ~91C then a voltage reading at a properly operating switch would show zero because it would connect it to ground. Although you can check the switch by just checking continuity between the pins when it is in boiling water. There should be continuity. If there isn’t, switch is bad. End of story.

Also, there are two sides to that relay representing 2 distinct circuits (for diagnostic concerns). Under operating conditions, 3 of those pins should show ground. with the only voltage showing up being on the pin with the BLK/YEL wire which is the battery side of the coil. The radiator fan should come on when you apply ground to the blue wire that connects the fan and the relay. The condenser fan on the other hand is on the other side of its relay so you would see battery voltage (or close enough) on 3 sides of that relay.

I think that welfare’s idea of checking the temp is a good one but my vote is the connector for the fan switch. cramming paper clips in there certainly wouldn’t have helped things. When the temp is above 90C use a multimeter to check for continuity between A&B on the fan switch connector while it is plugged into the fan switch. If there is not continuity, then unplug the switch and check the switch directly at the pins.

8

That’s all really good info Robin! The only thing that I’d like to add is that there’s a component which as of yet has still not been mentioned. That is the Radiator Fan Control Module (RFCM). The fan(s) are supposed to go on at various times according to different parameters, coolant temp, oil temp, whether the car is on/off, and whether or not the A/C is on. All of those systems send info to the RFCM and the fans go on according to all that info. I’m not 100% what exactly the RFCM does with those inputs but it’s definitely a part of the system. I also haven’t seen a RFCM go bad before, so I wouldn’t jump to the conclusion that it is the culprit, but if you exhaust your other options it would be something to consider. Although I’m not sure why I bothered bring this up, if you’re troubleshooting a problem like this you’re no doubt reading through your Helms manual and thus have seen the RFCM in the wiring diagrams.

9

Yeah, I was going to mention it, but I can’t see a situation where it could be bad AND the fans still run with the A/C. And FYI that A/C wiring diagram is a bitch to follow. I almost had to break out my circuits 101 book. Lol.

But you are right, it shouldn’t be ignored completely.

10

good call on the connector indeed. i’d check that out for sure.
but i’m not sure i follow on the thermoswitch. if you are probing at the switch before it is ground to the block, shouldn’t you be seeing voltage? i mean, it is before ground, no?

11

Yes it is before ground, but you have to remember that this switch functions only to connect terminal A with terminal B when the temp is above 90C (I call this “working” and “on” later). One terminal is always connected to ground (I’m at work without my manual, so let’s just call that one “B”) so when the switch is connecting those points, that other side “A” is now also ground. I am talking about this particular switch, obviously, but many of the switches in our cars operated this same way where they are actually connecting the circuit to ground, not to power. For stuff like seatbelt switches and shit like that, it is a much safer way to switch things.

Here is another way to think about it. That circuit with the switch (essentially) is composed of the battery, the coil in the relay which works to activate the fan, and the switch itself (we are ignoring the wires right now). When the switch is off and you are measuring it with a meter, there is no path to ground except through your Volt meter (connected to the wire going into terminal “A” with the red lead on the meter and to any ground on the car with the black lead). The Volt meter has a very high (theoretically infinite, actually in the Mega Ohm range) resistance whereas by comparison the coil in the relay has a very low resistance, so almost all of the voltage drop happens across your meter (so it would show very close to battery voltage when the switch is off).

Pretend the ammeter in the pic below is the coil in the relay and the resistor in the picture is the switch.

When the switch is open, you have to imagine that resistor isn’t there at all. Also, that coil in the relay has a small resistance in relation to the volt meter. Imagine the coil has less and less resistance. Eventually you are left with just a straight wire there and you are left measuring the battery.

But if that switch is working, it is closed, so it is like the resistor in the picture is a solid wire and by virtue of that both probes of your multimeter are connected to ground. Now, we tend to think of those grounds as being in physically different places and sometimes that makes picturing the circuit difficult; one is a black wire coming out of the terminal of the switch and the other one (black lead from meter) is probably connected to the engine or a bracket or something but ultimately both of those grounds (as well as all the others in the car) make it back to the negative terminal of your battery. When diagnosing issues, all those paths back become very important, but when you are trying to visualize the circuit, you have to picture them all as a single point for it to make sense.

Does that help you get it at all? It was a very long winded response and I’m not sure if it was clear what I am trying to say. I made it more basic than I think you needed welfare, but I thought it might help someone else to get a handle on how to visualize this stuff.

One last thing to add, when I say ground on something like this, I do mean the Helm’s definition which is usually under 1V. That switch won’t be perfect and so will have a little resistance and so it won’t have an absolutely perfect path to ground.

12

will i know the circuit is good I have bleed the air out the system. but I am trying to get my fans to come.

I have read the the computer also controls the fans…

13

There is a timer box that under some conditions can cause the fans to come on, but it does not “control” the fans in the way you are suggesting it does. With the conditions you have described, it would not factor into the problem you are having.

What do you mean by “it only does it sometimes”?
Have you tested the switch from the back side of the connector (while the connector is still plugged in?) so you know the connection between the switch and the connector is good?
Have you verified that when the business end of the switch is submerged in boiling water on the stove that the resistance between the two terminals is almost zero?
Those are your next two steps.

14

buymysoul, your detailed description is much appreciated. and daintegra, not trying to hijack. i think the full understanding of this circuit is important to your solution.
so if both terminals of the switch are ground; terminal B constant, and terminal A switched, where in the circuit is battery voltage applied? it must be before the relay. but what makes electricity flow through the relay and, ultimately to the fan motor and to terminal A, when closed. i mean, if electricity follows the path of least resistance, the relay would be higher resistance than the switches terminal B (ground). wouldn’t electricity just flow directly to terminal B?
not questioning you here, by any means. i know you have an understanding of the circuit, and as you’ve mentioned, many of our cars functions rely on circuits very similar to this. i’m just curious is all

15

Ok. Here is an awesome picture of the system.

I know you guys are just shocked with awe at how great my drawing is, but calm down and I’ll explain it:
The important thing, and the really cool thing about relays is that in that picture, when current flows through the coil of the relay (on the right side) the switch in the relay on the left closes (I put a line between them because it helps me visualize that one side is controlled by the other). I said the cool thing because the current on the right side, that activates the switch, can be very small compared to the current going through the fan side. That coil is also where all of the voltage (theoretically) drops in that side of the circuit.

welfare, as far as you specific question, you have to remember that while people do say that “electricity follows the path of least resistance” this is really a pretty significant over-simplification and misnomer. ALL of the electricity doesn’t follow the path of least resistance, just a proportional amount of it. If you have two resistors connected to the same battery and to the same ground, and one is twice the resistance of the other. 1/3 of the current will actually take the path of more resistance. But as far as your follow up, the electricty DOES flow directly to terminal B and then to ground. Luckily it has already gone through the relay and switched the fan on.

I’ve tried to make the drawing simple but you can see that the A/C switch essentially allows the current to still find a path to ground even if the fan switch isn’t working. This is why it has to be either the connections in the plug or the switch itself (since the fans turn on when you cram a paper clip in there).

Does my crappy little drawing make it any clearer what I’m trying to say?

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Not a very large pic so it’s a bit hard to read, but here’s the actual diagram in the Helms:

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Hey! You trying to steal the glory away from my awesome drawing?! J/K

Damn. I had forgotten about that drawing. The one from Canada on the left pretty much shows what I was trying to in my crappy little one (which was basically a simplification of that right hand drawing.)

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crystal. and hey, thanks for taking the time. really appreciate that a lot.

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how come the diagram in the helms there doesn’t show a relay with non a/c models?

20

No problem, sorry I don’t stick around here more. I tend to show up for a month and then disappear for 6…

I did figure out how the fan timer works, but it doesn’t seem appropriate to post it in this thread. I can say that there is no way it could (based on the FSM diagrams) impede operation of the radiator fan. Well, OK, if that top right wire (YEL/BLK) somehow shorted to ground internally, that would make the radiator fan not work, but it would also blow fuse 21 so I’m not counting that.

The condenser fan is another story and is completely at the mercy of that timer.

Incidentally, removing that timer is a piece of cake: just jumper the YEL/BLK wire (pin 2) to the YEL/WHT wire (pin 1). It will still come on when it is supposed to with the A/C and all that jazz, and it will also come on any time the radiator fan kicks on, just like it does stock.

You could also jumper WHT (pin 5) with YEL/WHT (pin 1) and get some interesting results. If I’m reading this right, in that configuration, your condenser fan would stay on (even if the car was off) until your coolant temp in the head got below 90C AND only if your A/C switch AND/OR the blower fan in the car was off.

Anyway, at this point I’d be willing to bet cash money that it is the connector on that switch or that the water temp isn’t actually getting above 90C when it is “over heating”.