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View Full Version : Heat & A/C "fan fail" relay



DeLorean
06-24-2011, 11:05 AM
My car amazingly still has it in place, and it seems to maybe? work. I was getting the "fan fail" light illuminating yesterday on a long drive, however it was coming on only intermittently, and then the fans would start and the light would go out.

Is this a sign that the relay is failing? I have been planning on doing the simple 3 wire by-pass of this relay, and I guess I should do this sooner rather than later.

David T
06-24-2011, 11:12 AM
There are some things that will just go bad. Two of them are the Ducy alternator and the blue Fan Fail Relay. If they still work, great, but they will fail and not when you want! It is like running on the beach where you know there is broken glass. Sooner rather than later you will get cut (stuck).
David Teitelbaum

Farrar
06-25-2011, 01:18 PM
Technically, it's not a relay; that's why the Y-jumper works. Just wanted to mention that to avoid confusion.

Dave M (Bitsyncmaster on DMCTalk) has come up with a drop-in replacement Fan Fail Module which serves the purpose of the "fused jumper solution" plus light functionality without the typical wiring mess. In my opinion, if it's as good as his Dome Light Module then it's worth every penny.

Edit: There is at least one owner out there who has re-designed the circuit to use one relay for each fan, using the old Fan Fail Module socket for the "second" fan relay. It seems to be also a very good solution, also. I had an idea to do something similar, using a separate CB and relay for each fan, but I have since lost the schematic -- sorry.

Farrar

ramblinmike
06-25-2011, 01:22 PM
Does the original fan fail module fail because the current goes through the traces on the board?

Farrar
06-25-2011, 01:36 PM
Does the original fan fail module fail because the current goes through the traces on the board?

From what I remember, that's correct -- basically shoddy soldering causes the unit to fail.

Farrar

Bitsyncmaster
06-25-2011, 01:37 PM
Does the original fan fail module fail because the current goes through the traces on the board?

I've never see the original fan fail unit but from what I've see with the other circuit boards my guess is yes. The fan current goes through copper traces on the board. If it's single sided circuit board with light copper (1 oz.) then most likely things get hot, melt and solder joints fail.

Now would it work with the new lower power fans? You would have to so some testing to determine that.

Farrar
06-25-2011, 01:51 PM
Now would it work with the new lower power fans? You would have to so some testing to determine that.

Good idea, Dave!

Farrar

DMC3165
06-25-2011, 09:57 PM
Dave M (Bitsyncmaster on DMCTalk) has come up with a drop-in replacement Fan Fail Module which serves the purpose of the "fused jumper solution" plus light functionality without the typical wiring mess. In my opinion, if it's as good as his Dome Light Module then it's worth every penny.


Farrar

+1 on this.
I just purchased this from Dave and it works great! This is a fantastic improvement over the y jumper and I'm happy I stumbled across it. I'd recommend it to any owner that currently has that slot jumped.

DeLorean
06-27-2011, 11:37 AM
So what should I do with my "all original" fuse box update wise? I should get rid of the fan fail relay and replace it with what if I don't simply do the 3-way jumper? Also, I noticed a lot of people have the fan-zilla products in their fuse panels, what about that?

Oh, and my heater/AC motor seems to be tripping the 25 amp breaker occasionally when it is at full blast. Is that OK to simply up to a 30 amp breaker? What fuses do I have to worry about melting in my panel because that has not happened yet, and I would prefer to keep it that way.

Chris4099
06-27-2011, 01:12 PM
Those Fanzilla like products are really no longer made (and really kind of outdated solution with low current fans being available). Unless you find somebody that has one stashed away, your only current options are a jumper or Dave's digital module. You can also do what I've done (and Farrar mentioned) and rewire the whole thing to use two relays (one for each fan), but that's not a simple/quick solution.

As for the fan CB, upgrading it to 30 amp is recommended for the reason you are experiencing.

When it comes to fuses, number 7 (fuel pump) is the most common one to melt down. At the very least, make sure the contacts for it are clean and there is no corrosion on the fuse blades. Going through all of them and replacing the fuses with new ones is a good idea too. If you are up for more work, contact DMCH and they can provide new fuse contacts (without the replacement panel). I haven't seen them myself, but they say they are heavier gauge, so they should provide stronger contact and help prevent any future melting.