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Heater Fan has power/not working while in car

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I've been at this for some time so I need some idea what to try next.


This is a '74 260z that formerly had an A/C. The original controls are still there but the vacuum tubes are disconnected. The fan was not working.

1) I removed the fan and when I applied power to the blower motor connector, it ran at full speed.

2) I checked the blower control switch using a continuity meter and each position seems to work.

3) The power relay puts out 12 volt with the ignition in the on-position.

4) I verified the proper electrical connections using the color codes on the attached figure and there are a lot of them.

5) I traced (using a continuity tester) the Green wire from the power relay to the heater connector where it became a white wire to the blower motor connector.

The voltage at the white wire on the blower motor connector ranged from 12 volts (fan of) to less than 1 volt at the 4 setting. I'm a little confused as to how this is supposed to work and why the fan should be off (which it is) at 12 volts when if I remove the fan and apply 12 volts directly to the blower motor connector the fan runs.

Can anyone tell me what to try or test next?

Thanks for your time...


AC fan.jpg

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That white wire should have a strong healthy 12V on it any time the key is in ACC or beyond, regardless if the fan switch is turned on or not. So there's clearly a problem on the power delivery side of things. You have "some" power at that white wire, but it's not a good strong connection.

First, I would make sure the fuses are good. I think heater is powered by either the third or forth one down on the left column of the fuse box, but while your under there, you may as well take a good look at every fuse. Take them out, look at them in good light, and gently clean up the brass fingers of the fuse block.

If all the fuses are proven to be good, I would take a look at the "power relay". (The device in the lower right of the diagram you posted.) If that relay is having a problem like a bad ground connection, or dirty contacts, then the fan won't get strong power. Is that relay screwed to the body? If so, that's how it makes ground connection. Make sure that isn't dirty.

For testing the power relay you could jumper it out of the circuit by connecting the L wire to the G that diagonal from the L. If you do that, it shouldn't matter whether the key is ON or not, and the fan should get power.

Good luck with the troubleshooting, and let us know what happens.

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Thanks CO, that's a start. 

Diagram BE-53 shows fuse 5 counting down on the left side powers the blower.  I'll clean it up as well as the fuse-box clips.

I'll also try what you suggested for the relay. I had replaced it with a used relay because the original one had a fried wire.

Thank you for the help on this. I'd like to get this working so I can drive this car into late fall. 

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Well... when I jumper the L & G wires the fan runs at full speed even with the ignition off. 


1) I'm assuming that means I have a bad relay.

2) Can I rejuvenate a relay by opening it up and cleaning the contacts?

3)  Can I use a modern relay or do I need to hunt down another used one and keep my fingers crossed?

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First off, just a point of clarification... You said that when you jumper L & G wires "the fan runs at full speed". Do you mean that 1) the fan runs at top (full) speed all the time, regardless of the position of the fan speed lever? Or do you mean 2) the fan runs at the correct speed (depending on the position of the speed lever) and by "full" you mean "not sluggish". I'm assuming "2", and I will move ahead based on that assumption, but I just wanted to check.

So assuming the fan behaves "correct" with the jumper in place, that's good, but it doesn't necessarily mean that the relay is the problem. There are still other things that could be causing the issue, although the relay is suspect.

So with the relay connected as designed, you should be able to hear (or feel) it click when you turn the key from OFF to ACC or ON. You should also be able to measure the voltage on the other L wire (not the diagonal one, but the other one) go from zero to battery voltage when you turn the key to ACC. This other L wire is the actuation control wire and it should have 12V on it any time the key is in ACC or ON. When this happens, the relay should click closed.

Can you snap a picture of the relay? I'm still unclear how it makes it's connection to ground, and that could be a problem area as well. It appears to be internally connected to it's metal shell and that shell is then screwed to the body where it mounts?

I'm not yet ready to condemn the relay, but if you do get to that point, I don't see anything special about it. I think it would be easy to replace it with something generic.

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Oh, and don't worry. We'll get you into late fall! In fact, you already have a workaround.

Just keep that L to G jumper in place and make the promise that you will never ever ever forget to turn the fan switch to OFF when you park the car so you don't drain your battery.  LOL

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CO.. I had to go back to the car and check but yes, with the G&L jumpered, the fan does obey the speed control and I get the 4 speeds and off.

I do hear the relay click when the ignition is turned on with the relay connected.

With the relay disconnected again, I'm seeing 12V on the non-diagonal L wire. Interesting that I'm seeing 0.1V with the ignition off. 

The relay appears to be grounded to its shell; however, there is a fourth wire on its connector (seen in the photo as a head-on view) that has no matching wire on the mating harness connector. This could be a ground that Nissan chose not to implement. The fan relay is just to the right of the "Ground" tagged wire. The ground wire was added because I was worried that there were too many ground wires from different components connected to a single grounding wire in the harness and was a potential cause of some wire melting events I experienced. To the right and up a bit are two screws that mount the power relay to the relay panel. That is how the relay shell is grounded.

As you can see, I went a little crazy with the label maker. 



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Haha! Have label maker. Must use it! Just kidding. I feel that you can't have too much explanation. I've opened things up sometimes and seen scrawled writing inside things like that relay. And the scary part is... it's my handwriting, but I don't ever remember being in there before. At least with a label maker, you have plausible deniability!

So if the relay is clicking when you turn the key to ACC, now I'm almost ready to condemn the relay. I suspect the contacts inside are burned up or so dirty they can't supply the motor with the necessary current. You can probably open it up. Most of the relays of that era have little bent in tabs on the underside that you can easily unbend to pull the shell off.

But before you do that... Are the contacts on the other mating half of the relay connector as clean as the side in the pic? If so, they look fine.



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Yeah, it sounds like that relay isn't switching the way it should. A little surprising to me though, since it really isn't that much current we're talking. That coupled with the fact that you already replaced that relay once before because of a burned wire. Makes me think there could be something else going on, but making sure that relay is working properly is the next step. You could electrically test that relay in place by measuring the resistance between the G and the diagonal L. With the relay connected normally, you could*:

Make sure the blower speed switch is OFF.
Connect an Ohmeter between the G and diagonal L on the relay. (Stick the probes into the back of the connector going to the relay).

With the key in the OFF position, you should measure infinite resistance (no continuity) between the G and the diagonal L.

Then with the key in ACC or ON, you should hear the relay click closed, and you should measure nearly zero resistance between G and diagonal L. Like less than one Ohm.

Or you could open it up and have a peek inside. Whatever is easiest.   :)

* Note that this test method assumes that relay doesn't power a whole bunch of other stuff other than just the blower motor. I didn't dig through the wiring diagram enough to know for sure, but I think this should work.

Edited by Captain Obvious
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I removed the relay cover and one of the points looks rounded. I lightly sanded them with fine sand paper (wish i still had my points file).

With the ignition OFF/fan OFF/Relay installed: There is 12 volts between the diagonal G & L wires while back probing. Therefore there must be continuity. 

With the ignition at ACC/fan OFF there is no click,  points are open, between G&L 0 Volts, 37 ohms.

With the ignition at ACC/fan ON there is no click,  points are open, between G&L 10.2 Volts.

A relay is inexpensive enough, maybe I should buy one.

As a side note, I found that plugging/unplugging the relay blew a fuse but not the one for the blower motor. For the dash lights (not working right now) and the voltage regulator under the hood.





Edited by Jeff Berk
Correction to troubleshooting results
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OK!!!!!! I think I'm there...THANK YOU  CO

I went to Autozone and picked up a new relay and wired it in, adding a ground wire since the new relay had a plastic shell.

So far it seems to be working. Now to secure the wires so it doesn't look jerry rigged. 

Now onto the next electrical glitch.

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  • 2 years later...

Jeff, or others willing to help a lost sole.

Just wondering was it the fuse blow that caused your dash lights to go out? After your replaced the relay and the fuse did your dash lights then work?

I have a 73 240 and my accessory relay sometimes does not work, and I have not been able to get my dash lights to work at all. I am doing a complete restoration and all

other lights, controls are working. I measure 11.7 volts at the rheostat.  Should I just go ahead and replace the relay? What info. did the parts store need to find a replacement?

Thanks Craig  

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It's been a long time since I had that issue so I don't recall the details.

The only problem with a new relay is that the plug will not match. It's just a "standard" relay.

I don't think the relay replacement corrected the dash lights but I cannot recall the fix. Just wondering, did you install LED dash lights like I eventually did? You can't use a standard rheostat to control them.

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I was doing some electrical work on my '74 today and realized that the way I resolved my dash light was to install a second fuse panel and ran the dash lights off of it. I kind of recall that I had fuse blowing issues so I split up the components leading to the circuit using the second fuse panel with four separate circuits.  I figured that the component causing the fuse to blow would be narrowed down but no fuse in the second panel popped. So I just kept the troublesome circuit split into multiple separate circuits. 

So, I guess I never figured out the reason why my lights were not working but found a workaround. 

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Thanks for getting back. My dash lights was not a problem. It was the DA who could not see that the lights were on. With bright shop lights and not starting the Z, I was not able see that they were on. I just added a fuse and eliminated the relay for the blower motor and all electrical systems are now a go. 

Windshield gets installed tomorrow.

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