'77 2500M - No power to fans

[jastx]

Neither my main electric fan behind the radiator or my auxiliary electric fan in front of the radiator are functioning. Can you please help me diagnose? I have verified that both fans run with power direct from the battery so the problem is power is not getting to the fans through the wiring.

According the manual the fans are fused at the bottom fuse block (main fan on top, aux on bottom). The fuses are intact. Can you please help me understand the wiring and relays?

Fuse Block photo below with labels.

Power to the bottom fuse block seems to come from the top fuse block via a black wire. From the top fuse block another black wire on the same spade plug connects to the relay on the bulkhead, labeled photo below. A black wire from the bottom fuse block also connects to this relay, and two other black and one green wire also connect to this relay going somewhere unknown.


Can you please explain what this relay if for and how it works with its connections?

The auxiliary fan relay is on the passenger wheel well (right side in USA), see below. It connects to earth and to the otter switch. Two other connections go somewhere else.


Can you please explain how this relay works with its connections? I'd like to test it by applying power to the right connection.

All advice appreciated.

Edited by jastx on Sunday 18th November 23:36

[oldgeebee]

The relay coil is connected between W1 and W2 and the contacts are the C1 and C2 connections - see here. The double spade terminal at C1 is usually the "output" with a fused 12V connecting to C2. Putting 12V across W1 and W2 should activate the relay - you should hear a clicking noise as it switches over and C1 should then be connected to C2.
If the relays check out OK then suspect an earth issue somewhere - trace back the earth wires from the fans to see where they go and clean up any connections you find in that chain.

HTH

GB

[jastx]

Thanks GB. So if I understand correctly, based on how my auxiliary relay is connected as shown below...

The Otter switch connects to earth from one side and to W1 on this relay from the other side so it's function must be to connect the relay coil to earth to activate it when the threshhold temperature is reached. The Blue wire connected to W2 on the relay must be power for the relay coil. The black wire connecting from C1 to earth would therefore be earth for the fan and the black wire connecting to C2 connects the earth to the fan when the relay is activated. So, the relay is all about connecting the fan to earth so it runs. Is that correct? If so, with the relay in good order connecting W1 to earth instead of the Otter should activate the relay, correct? If this doesn't work, either the realy isn't working or the relay isn't getting power through the blue wire connected to W2, correct?



One more question, please. I understand how this relay is related to the aux fan. What is the relay on the bulkhead left side (2nd pic in orginal post) for?

Thanks!

Edited by jastx on Monday 19th November 21:12

[oldgeebee]

jastx said:

So, the relay is all about connecting the fan to earth so it runs. Is that correct?

Yes

jastx said:

If so, with the relay in good order connecting W1 to earth instead of the Otter should activate the relay, correct?

Yes

jastx said:

If this doesn't work, either the realy isn't working or the relay isn't getting power through the blue wire connected to W2, correct?

Yes - could be the Otter switch isn't working correctly or it could be the earth from the relay isn't making a good connection to Bat -ve.

jastx said:

One more question, please. I understand how this relay is related to the aux fan. What is the relay on the bulkhead left side (2nd pic in orginal post) for?

Not sure. You indicated that you had 2 electric fans so what controls the other fan? Is the 2nd relay connected to this fan?

Strange enough, I saw a link on the S series forum today which referenced a Lucas fault-finding guide here. This seems to describe an Alternator circuit with battery-excited system (types 10AC and 11AC) which uses this relay in the control circuit (see page 34 of the linked document). If your alternator is an ACR type then this won't be the use of the relay and I would then need to defer to others who are familiar with the US 2500M wiring spec.

GB

[jastx]

Thanks again GB! I believe I understand it better. Not sure if the relay on the bulkhead is related to my fans or not. Here is a better photo for those who might be able to identify it and enlighten me.


I have done some testing and manually fired the aux fan relay by simply earthing the otter switch connection. The relay may have been stuck but is not any longer. Unless the otter switch is bad, my auxiliary pusher fan will come on as it should. I may pull the otter to test it.

I have a confusing condition with the primary puller fan. It will not run with its normal power and earth connections but will run with its normal earth with power directly from the battery. I have a continuity tester that also lights 6 volt or 12 volt LEDs when power is present and also have a multimeter. With the ignition on the + wire to the fan reads 12v dc on the continuity tester. With the multimeter 11.44 volts (when earthed to a spare tire bolt on the frame). Seems adequate, doesn't it? Yet neither the primary or aux fan will run using this + wire. Not enough amps maybe?

What should I do to further test or to correct this? I have cleaned the connections on the fan end. I suppose pull and clean all the connections on the fuse block?

Thanks for your advice! I think I'm getting close!

NOTE: On further checking two wiring diagrams (neither of which match my car completely) I believe the primary (puller) fan has a + connection directly from the fuse block (no relay) as well as its own earth connection to the frame and should run whenever the ignition is ON .

Edited by jastx on Tuesday 20th November 03:05

[oldgeebee]

jastx said:

I have done some testing and manually fired the aux fan relay by simply earthing the otter switch connection. The relay may have been stuck but is not any longer. Unless the otter switch is bad, my auxiliary pusher fan will come on as it should. I may pull the otter to test it.

Sounds to me like the otter switch is the problem here. I'd be surprised if the relay was sticking but has been known to happen!

jastx said:

I have a confusing condition with the primary puller fan. It will not run with its normal power and earth connections but will run with its normal earth with power directly from the battery. I have a continuity tester that also lights 6 volt or 12 volt LEDs when power is present and also have a multimeter. With the ignition on the + wire to the fan reads 12v dc on the continuity tester. With the multimeter 11.44 volts (when earthed to a spare tire bolt on the frame). Seems adequate, doesn't it? Yet neither the primary or aux fan will run using this + wire.

This is confusing because my first reaction is that it's the puller fan earth. If the multimeter is across the + and the chassis frame this indicates the 12v feed is OK - when measured to chassis. To check the puller fan earth connection you need to measure direct across the fan - use the fan earth pin, not the chassis. A low reading here would indicate a bad earth line from the fan. However, if it runs OK with a direct feed from the battery, this would indicate the earth is OK.

jastx said:

Not enough amps maybe?

Well, the only thing limiting the amps would be thin wire or a high resistance connection. If the fan is not running, the 11.44v you are measuring should be the same as the battery voltage. If the battery voltage is higher then that indicates that current is flowing so maybe the fan has stalled, but that seems unlikely.
As a general rule, when looking for this type of fault, measuring voltage drops is the way to go. With the fan running (with a wire direct from the battery) is there a voltage between fan earth and chassis? If so, this would indicate a high resistance earth (i.e. bad connection). If you use this approach around the circuit, you should eventually track it down.
On the other hand, cleaning up all the connection you can find that are in the fan circuit should also solve the issue and may be a quicker, if less theoretical, solution!

Good luck!

GB

[jastx]

It's the power lead. With both fans near each other its easy to switch leads. Puller fan won't work with push fan earth. Pusher fan won't work with puller fan +. Puller fan will work with pusher fan +.

So I'll try cleaning connections up by the fuse block.

I also found another diagnosis of sorts that may have something to do with it:

http://www3.telus.net/bc_triumph_registry/smoke.ht...

GB, thanks for your help and responsiveness. It really helps to have an experienced person talk through it with me. I understand the situation much better now. With the problem isolated, I can fix it.

[oldgeebee]

Sounds like you're on the right track.

"Tune for maximum smoke" as my old electronics teacher used to say.

GB

[jastx]

Finally had SUCCESS with powering the fans. To bring closure to this adventure:

1. The relay on the bulkhead whose function I wasn't sure about WAS involved with the fans. The relay coil is powered by a pair of black wires and that come through the bulkhead from inside the car. I don't know where they come from inside the car but don't care because they work when the ignition is in the ON position. The function of this relay is to provide power to one of the fans through a wire that connects from the top section of the Bottom fuse block to the relay (C2), then back from the relay (C1) over another wire to the bottom section of the Bottom fuse block.

With my fans' power leads on the fuse block connected according to the manual (primary fan on top), this arrangement affects power to the secondary fan. I'm not sure this is correct and I don't know what the logic is supposed to be. With the ignition off, there is no power to the fuse blocks so neither fan can work. With power on, this arrangement sends power directly to the primary fan from the fuse block. Power to the aux fan is "switched on" by the bulkhead relay I described but the fan doesn't operate unless the otter switch activates its relay by the wheel well. Therefore, it goes through TWO relays to work. I suspect the primary fan should operate via the bulkhead relay and the aux fan through the wheel well relay. I think I will change the connections to work this way.

Can any 2500M owner please tell me how their fans are connected to their fuse blocks and how their fuse blocks are connected to the bulkhead relay? Or does anyone know how the fans and relays are supposed to be wired?

2. My "No Power" problem with the fans turned out to be the original, factory spade-plug-terminated wires between the fuse block and the bulkhead relay. There was at least one bad connection where the wire was crimped to the spade plug. I replaced these wires and spade plugs with new and problem solved. Now both fans work. During the process, I also took the cover off the bulkhead relay to examine it. It was perfect inside and worked perfectly. I just cleaned up the contacts a little and put it back together.