Bad ground on fans

[FurryMcMonst]

I'm trying to fix my wife's friends 2000 Taurus. (Single mom, four kids, not much money, etc.)

She said the car overheated in city driving and I observed that the fans don't turn on. I pulled out one of the fan connectors and as the car heated up just over the middle mark, I observed 14 volts on one of the two red/orange wires.

It seemed odd that voltage would be applied and the fans wouldn't come on so I shut everything down and tested the resistance of the ground (black) wire of the connector to the engine block. It read infinite leading me to conclude that the problem is a bad ground connection.

Does anyone know where the actual ground connection is located for this circuit?

Are these fans wired in parallel?

There are two "hot" wires. Are these two speeds to the fan?

Any hints on how to find where the ground ultimately connects to the frame? I tried following the wire but it's next to impossible for a novice like me.

I'm at the point where I I'm thinking of just tapping into the ground wire and running a new bit of wire to the frame. Any comments on that approch?

TIA

[shorod]

I don't have a service manual for the 2000 Taurus, but I do for 2002. I expect they are pretty similar.

For the 2002, the wiring diagram is interesting for the fans. There is a current limiting resistor for low speed operation. The Engine Cooling Fan Relay in Relay Center Box 1 switches in the current limiting resistor and runs the fans in series. During low speed operation, all ground occurs through the hard ground at Fan #1 and both fans should run as long as both fan motors work. Since they are in series, if one fails, the circuit will not be completed.

During high speed operation it would appear that Engine Cooling Fan Relay in the Relay Center Box 1 switches out the current limiting resistor and allows no extra resistance to the fans and it appears that both fans should run (in parallel). However, for high speed operation, each fan has its own ground. Fan #2 is grounded through the High Speed Relay in the battery junction box during high speed operation. Fan #1 has a hard ground.

The diagram isn't real clear how the three relays operate, so the series connection of the fans versus parallel could be backward, but that wouldn't make as much sense to me. It seems for high speed operation they'd want full current to both fans as well as the parallel path for failsafe reasons.

The ground for both fans is spliced and ultimately terminats at location G105 located in the engine compartment at the front right hand side, about halfway between the passenger side (in the US) strut tower and the A/C accumulator.

-Rod

[FurryMcMonst]

Rod,

Thanks for the help. I finally got a chance to look at this today and at this point, I feel that both fans are bad. I decided to test them both by hooking them directly to the battery and nothing happened.

I removed both fans at that point and checked the ohms from the ground terminal to the other two terminals and both readings read infinite resistance. (The same on both fans.) I assume there should be a measurable but somewhat low resistance through the windings.

I'm puzzled about what the root cause could be. Have you heard of this happening before? I hate to put two new fans in and then have them both go bad right away because of some other issue. I would expect a fuse to blow in such a case but I didn't find any blown fuses.

After reading your reply I realized that I needed a schematic and actually found one online at a Russian website. The schematic shows a relay that connects ground so my initial premise of a bad ground was likely faulty. The relay would have to be closed to get the zero ohms I was looking for there.

The shematic is very puzzling as it shows the hot side of the circuit going directly to ground through that relay until the relay energizes and connects the ground. It has to be a mistake.

I would love to hear your ideas on what would make both the fans go bad.

Thanks.

Furry

[shorod]

Take a look at the diagram again. I believe the relay you are referring to that would ground the hot side of the fans is the "fan braking relay." As you may be away, one way of performing electric braking is to short the two terminals of a DC motor together. This is how many cordless power tools perform electric braking, and that's what's happening here.

So you've removed the fans from the car, checked for resistance across each fan motor independently, and connected each fan independently straight to a battery? And this was using the connection at the motor itself, not through some wiring harness? If the answer to all of the above is "Yes" then I suspect what happened is one fan failed initially, but because of the redundancy, you didn't notice an issue until the second fan failed some time later.

Granted your car seems a bit young for both fans to fail. Have you checked for voltage to the fan connection when the A/C is enabled? You might want to try that. If you see voltage, you should load the lines to make sure it's not a high resistance path that the high input impedance of your meter won't load down. You could either install the fans again and backprobe the connector (safely) or use an incandescent test light.

-Rod

[FurryMcMonst]

Originally Posted by shorod

Take a look at the diagram again. I believe the relay you are referring to that would ground the hot side of the fans is the "fan braking relay." As you may be away, one way of performing electric braking is to short the two terminals of a DC motor together. This is how many cordless power tools perform electric braking, and that's what's happening here.

You are right, it is labeled as the "fan brake relay". I've looked at this circuit again and just can't see how a hot voltage to a ground (that is broken between the fans) accomplishes what you say. I may be missing something.

Originally Posted by shorod

So you've removed the fans from the car, checked for resistance across each fan motor independently, and connected each fan independently straight to a battery? And this was using the connection at the motor itself, not through some wiring harness? If the answer to all of the above is "Yes" then I suspect what happened is one fan failed initially, but because of the redundancy, you didn't notice an issue until the second fan failed some time later.

Yes, I did exactly what you described. It seemed better to start there rather than tracing all through the circuit. In this situation at least it appears to have paid off!

Originally Posted by shorod

Granted your car seems a bit young for both fans to fail. Have you checked for voltage to the fan connection when the A/C is enabled? You might want to try that. If you see voltage, you should load the lines to make sure it's not a high resistance path that the high input impedance of your meter won't load down. You could either install the fans again and backprobe the connector (safely) or use an incandescent test light.

I have not tried this yet. Thanks for the suggestion.

I need to understand a couple of things and maybe you can help. In a normal operating Taurus of this year, should the fans come on right away when the engine is started? Or, do they stay off until a certain temperature is reached?

There are three wires on each connector to the fans. One is black and I assume ground. Do the other two wires correspond to high and low speeds?

If so, under what conditions should I see supply voltage on each of these wires? It sounds like one should trigger when the air conditioner is turned on. When should the other one trigger?

Rod, thanks very much for all your assistance.

[shorod]

When the fan brake relay is open, it shorts the supply side of the fans (which do not have battery voltage at the time) to ground. Since the other side of the fan is also tied to ground, it shorts the two sides of the fan motors together, causing the fan to slow down quite rapidly (electric brake). The fan brake relay is the only source of battery voltage to the fan circuit, providing either ground OR battery power to the fan relay, so under normal conditions you'll never have a scenario where the fans have battery voltage AND ground on the same line at the same time.

As far as the three terminals on the fan connectors go, you are correct that the black wire is the ground wire. The other two should be tied together (and the wire colors are the same - red/orange). They are parallel wires to support the current draw by the fan motors. They do not correspond to high and low speeds. That is done through the high and low speed relays along with the current limiting resistor which is switched in or out by the cooling fan relay.

The fans will only operate when the Engine Coolant Temperature (ECT) sensor determines the engine coolant temp is high enough to warrant running the fans or when the A/C or defrost is on and demands the A/C compressor clutch to be engaged.

-Rod

[FurryMcMonst]

Rod, thanks again. I'll go through the schematic again using your explanation.

When I did my first test that prompted this posting, I had unplugged the fan and waited for the car to heat up. At some point after the temp gauge went above the middle, I saw 14 volts appear at one of the red/orange wires and not the other.

It sounds like since you said the two red/orange wires are tied together that I should have read 14 volts at both red/orange wires. Since I didn't, do you have any ideas?

Also, the ground thing is confusing me. If the motor is off and I unplug the fan, if I measure resistance from the black wire on the plug to ground, should it read infinite or zero? (The ground relay is not energized and I'm not sure now if that breaks the ground circuit or not.)

Sorry for all the questions and thanks so much for helping.

[way2old]

You all got me confused on the fan braking relay. I looked at the Ford factory wiring and do not see any relay with that name.
Here is the diagram I have.

[FurryMcMonst]

Yours looks a little different than the one I have.

[shorod]

And as I mentioned, the diagram I'm using is for the 2002 model year, but it too is from the Factory Service Manual for 2002. Interesting that the wire colors match, but not the diagrams.

Furry, if you are measuring the wiring plug (not the jack/socket on the fan motor) black wire to ground, you should see only tenths or less ohms of resistance, essentially a dead short. It also would appear that the normally closed position of the fan brake relay (assuming your car does have this) is shorted to ground through the current limiting resistor. Therefore the same plug should show ohms of resistance to ground on the power wires, and both wires should read the same. The reading will depend on the resistance of the current limiting resistor. It appears the resistor is located near the fans, you may see if you can find it and test it for resistance based on the value that hopefully is listed on it.

Way2old, please let me know if for sure the diagram you posted is definitely for the 2000 model year. The fan brake relay for the 2002 model year is located in Relay Center Box 1.

-Rod

[way2old]

Hey Rod. The diagram came straight from Ford. I assumed it was the base Taurus. If Furry wants to PM me the VIN, I can get exact wiring diagram for that specific vehicle.

[shorod]

Wow, interesting. Last night the diagram didn't show up for me in Furry's post. This morning I look at it and it's different from what my 2002 model year diagram shows.

Going the route of providing the VIN to you may be the safest route. I could be sending him on a wild goose chase. No wonder my descriptions weren't making sense to him!



-Rod

[FurryMcMonst]

Guys, sorry for the late reply. Deadlines at work have kept me from getting back at this.

Here is the VIN: 1FAFP5520YG175953

I had someone else test both fans just in case and they are indeed both bad. I was told that the voltage could be applied and nothing would happen but if you spun the fan with a stick or something, it would then start.

Now, I see that new ones are expensive so I'm thinking of calling around the junkyards. What year models have fans that fit the 2000? Someone here in the Seattle area is parting out a 1996. I'm hoping those fans are identical and that they haven't been snagged yet.

Thanks for all the help.

[shorod]

It would appear from Fast Parts Network that the fans for 2000-2007 are the same, but not the same as the 1996 model year.

Rock Auto has these available new for just over $60 each that includes the blade, motor, and shroud. Keep that in mind when shopping for a good used pair.

-Rod

[Gizrat]

Hey I have the same issue with my 2000 taurus and was wondering if when you replaced the fans if that fixed your problem. My fan also works when it is spun.