Heating/ventilation blower relay ground issue

[Garrett]

In trying to diagnose an inoperative HV blower fan, I've found that the fan relay (#7 in the diagram below) is tripping when it makes contact with the chassis (fuse block mounting post). The fan works as it should (incl. switching on/off) when either 1) when the relay is not in contact with a chassis ground (unmounted), or 2) when it is mounted but the relay ground wire is removed from the fuse block mounting post.

The A/C blower motor is not similarly effected, it works all the time like it should. It is not effected by any of the above scenarios.

I have limited electrical diagnosis skills at best, any ideas what could be causing this?

I will mention in case it's related that though the A/C blower is working fine, the rest of the underhood A/C components are currently out of the car. Not sure if that's creating an open circuit of some sort.



Garrett

 

[Garrett]

Sorry, looks like the diagram doesn't show up in the post, but here's the link and the part number for the relay is 61311352232.

http://www.realoem.com/bmw/enUS/showparts?id=3435-USA-01-1973-E9-BMW-30CS&diagId=64_0883

 

[sfdon]

Whenever your blower relay is activated the blower fan will NOT work.
The contacts OPEN when energized.
Normal operation is for contacts is CLOSED with no signal.
The signal is the black wire at the relay.
If the relay is activated it is because your black wire has battery + on it.
The black wire has battery + whenever the AC blower switch is turned on.
Turn your AC blower knob off and your blower will work.

 

[Garrett]

So right now with the brown wire disconnected both blowers (AC and HV) work at the same time. Maybe that's the function of the relay, to isolate the two.

With the brown wire connected correctly and the AC blower switched off, the HB blower does not work. But in the configuration the AC blower does work when switched on.

 

[HB Chris]

That relays prevents heater fan from being on when you turn on A/C.

 

[Garrett]

Hmm, so which is more likely ... 1) bad AC switch (note that it no longer provides variable fan speed, but that's been the case for years without affecting HV blower), 2) bad relay, 3) open circuit due to missing AC components, 4) something else?

 

[sfdon]

Just pin out the black wire.

 

[Garrett]

(sfdon, apologies in advance as I will quickly demonstrate my lack of electrical troubleshooting skills...)

Just pin out the black wire.

The black wire is hot at all times, regardless of the A/C blower switch position ON or OFF. Is that what you meant ?

 

[sfdon]

That's why the relay is engaged.
Switch is bad

 

[Storage Andy]

I figured lets see whats up with the heater blower since I will need heat in a few months. Took the motor out and it is shot. Hard to turn and when I put 12v to it nothing. Went to see if it was getting power as well. No good. Went to the forum and found this discussion. Couple of questions for you guys. I don't have an A/C switch. I take it the heater fan switch is the one that is labeled Air Fan. Mine won't go all the way to fan. When I move it as far as it will go, about half way. I don't get power to the blower. Could that be due to the A/C switch missing? Or maybe a relay issue? As far as the A/C switch I have a Yellow wire with green and two blacks with white/grayish hanging out in the console. I assume these are for said switch.

 

[HB Chris]

Without A/C you won’t have an A/C switch in center console above the radio. The heater fan only energizes when lever is pushed past half way, it must be binding inside.

 

[Storage Andy]

Without A/C you won’t have an A/C switch in center console above the radio. The heater fan only energizes when lever is pushed past half way, it must be binding inside.

Thanks. I do have A/C just no switch. I take it that it's a project to make that fan switch work correctly.

 

[HB Chris]

Even with A/C but no switch the heater fan should work. It is only bypassed when A/C fan is turned on.