Alteration of Fan Fail Relay

[DMC-Ron]

I'm in the process of chasing down a cooling fan issue. The cooling fans stay on continuously anytime the ignition key is on (just started doing this). I was checking the cooling fan relay just to see if its contacts might be welded closed when I noticed an alteration of the fan fail relay done by the previous owner (PO). It looks to me like the PO pulled the fan fail relay and put individual inline fuses to connect to each fan. I'm guessing this eliminates my fan fail feature but perhaps the PO felt that the individual fusing was a good trade-off. Any concerns with this?

By the way, the cooling fan relay is just fine. I'll be checking the otterstat next. I suspect it may be stuck on.

Oh, while I'm here... I also noticed the fuse #7 looks like it may have gotten hot (see close-up of fuse panel). Kind of surprised since this fuse is listed in the owners manual as Lambda control unit and fuel pump. I wouldn't expect excessive current. Is it common for this fuse to get hot?

My final peeve is with the wiring schematic. Many of the relays are shown as blocks and you can't actually see their coil circuit and contacts. The operation of the fuel pump is an example where it's hard to tell how power gets thru the RPM relay to the fuel pump. On the other hand, I'm more than pleased that we have a seemingly very complete electrical schematic as a reference.

Thanks,
Ron

[Josh]

The fuses in the fan fail relay are a very common modification. The fan fail relay was a poor design right from the factory, you will not find many cars with it in use.

[JAS037]

DMC-Ron, Take a look at this link. It's a section from the DMC knowledge base, and explains a lot about the problems in the fuse/relay area. And you'll see the explanation regarding the fan fail jumper you see.

http://support.delorean.com/kb/a53/electrical-relays-and-relay-updates.aspx

[David T]

It is also common to see heat damage to fuse #7. The fuel pump and electrical circuit draws too much power when you have bad connections in that circuit and/or the fuel pump wearing out. Pull both wires off the "O" switch, the fans should shut down. Common for it to go bad too. When replacing it you also replace the seal. NEVER use any sealer on that seal and if you don't have the clip, use a strap-tie. You don't have to drain the system, do it fast.

[NckT]

I've seen it a couple of times where the mode switch was on air-conditioning mode (dial selected to the legend that looks like a snow flake) and that a previous owner had linked out the air conditioning low pressure cycling switch out to compensate for a low refrigerant charge.

Make sure the mode switch is in the off position, and check at the low pressure cycling switch area, on the silver coloured accumulator at the front right wheel/ tyre area. You could confirm this by removing Fuse No. 10.
(Fuse No. 5 supplies the current to the "otterstat" coolant temp switch in the engine bay left hand side from the rear, at the left mouse metal coolant pipe, wires being underneath)

It wouldn't be the first time that someone may have added a secondary switch to run the fans as a precautionary measure too, and this has been left in the ON position. Someone may have added a small switch on one of the blanks next to the window switch at the centre console, for example.

Good luck :)

Nick

[DMC-Ron]

Thanks to all for the tips.

Josh - kind of interesting to discover all these quirks. Seems like the fan failure notification was a good idea... to bad it didn't work. Good to know that what I'm seeing was a common fix.

Jeff - thanks for the link. The DMC reference mentions the "improved" relays as Bosch relays indicating they last longer than the NOS replacement relays. I notice that my relays are Bosch and they have a red diagonal stripe. Were Bosch the original relays, did they switch to Bosch in the later cars (83), or perhaps the previous owner replaced? Anyway, if I have Bosch, am I good for now?

David - succinct advice for the fuse and otterstat. If the otterstat turns out to be the culprit, I was hoping I could do a "finger-in-the-dike" replacement and not have to drain the coolant. Your comments are appreciated and encouraging.

Nick - Yep, if it isn't the otterstat then the mode switch would be suspect. However, my AC is working and it does turn off with the mode switch.

Thanks all,
Ron

[Christian Dietrich]

I would also change every single one of those fuses because the script on the fuse looks identical to the original fuses which should be definitely replaced.

Sent from my SM-N920P using Tapatalk

[David T]

The fuses don't have to be replaced BUT. I would remove each one and clean the blades so they are shiny, make sure each blade is gripped tightly by the connector in the fuse block, the correct size is in the correct spot, and there is no heat damage. If any of the fuses are showing heat damage, then of course they should be replaced and that circuit checked.

[Chris 16409]

The DMC reference mentions the "improved" relays as Bosch relays indicating they last longer than the NOS replacement relays. I notice that my relays are Bosch and they have a red diagonal stripe. Were Bosch the original relays, did they switch to Bosch in the later cars (83), or perhaps the previous owner replaced? Anyway, if I have Bosch, am I good for now?

Most of the original "changover" relays were unmarked. The colored one are marked "Pektron". The lambda relay was the only Bosch relay in the two relay banks. In the early days, vendors offer all metal Bosch relays as an upgrade. Later, some offered black plastic Bosch Relays. They latest have been the Purple plastic ones. I believe Bosch spun off their manufacture to Tyco. I would say the metal Bosch relays are fine.

[BLWNAWY]

Sorry, but in my opinion the 3-wire jumper promoted by DMCH is only a band-aid. I'm surprised no one mentioned the old trick of re-wiring the fan fail relay socket to match the fan relay socket next to it, thus separating the two fans to separate relays and putting half the load on each. The added benefit is that should one of the relays fail in the future the other fan would continue running. Along with that, upgrade the fan circuit breaker to a 40 amp post-style breaker. Yeah, I know the purists don't like modifying the original wiring, but in this case it is a huge improvement. Just be sure to make a note explaining this change and attach it to the underside of the plywood relay access cover. I did this modification to all of my cars in the old days and it worked great.

[David T]

You're right about the jumpers being a temporary fix. On many cars it has worked for over 30 years! The factory was supposed to come out with a better solution but that never happened. Your mod is OK but "back in the day" when Fanzilla was available, that was the better, (expensive), more elegant solution along with changing the breaker. I personally have seen those jumpers burn so if anyone is still using them (lots are!) they should be inspected regularly. Using those jumpers you lose the Fan Fail warning light, IMHO a good thing to have.

[DMC-Ron]

Reasonably sure the fuses are all original. I'll take David's advice - remove and polish each blade - insure a snug fit when reinstalling.

Has anyone used Corrosion X to spray electrical terminals? Several aircraft mechanics I know swear by it. They claim that once treated, the terminals are almost impervious to corrosion. A boat owner I know swears by CRC 6-56, also for cleaning an protecting terminal connections (among other things). I would think this treatment would benefit the fuse block connections. But perhaps overkill since the fuse panel is somewhat sheltered and dry?

Darryl - Splitting the circuit so each fan could have it's own relay seems a good notion. Reworking the wiring on the relay sockets would be fairly straightforward. However, I will soon be installing the lower current fans from Toby, so maybe a mute point.

David - I also think the fan fail feature (if it worked correctly) would be very beneficial. Does Dave M have a replacement gizmo for this?

Thanks,
Ron

[Bitsyncmaster]

Darryl - Splitting the circuit so each fan could have it's own relay seems a good notion. Reworking the wiring on the relay sockets would be fairly straightforward. However, I will soon be installing the lower current fans from Toby, so maybe a mute point.

David - I also think the fan fail feature (if it worked correctly) would be very beneficial. Does Dave M have a replacement gizmo for this?

Thanks,
Ron

When you do the relay split, you loose the fan fail socket. Most relays are rated for 30 or 40 amps and with low power fans your drawing less than 20 amps total.

Yes my electronic fused fan fail unit turns on the fan fail light if either fan runs less than 4 amps or greater than 18 amps. It will shut down that fan if current exceeds 20 amps. It also delays turning the second fan on by two seconds.

[DMC-Ron]

Yes my electronic fused fan fail unit turns on the fan fail light if either fan runs less than 4 amps or greater than 18 amps. It will shut down that fan if current exceeds 20 amps. It also delays turning the second fan on by two seconds.
This sounds excellent. I'll be in touch.

Upon further investigation into my cooling fan issue... it's my otterstat - the contact is stuck in the closed position causing my fans to run whenever the key is on. I was pleased to see that the replacement cost is reasonable from DMC.

Thanks,
Ron