Charley B

I have an '82 with a set of S4 cooling fans installed.
The fans aren't working.
I have hot wired the fans and verified they are working fine. I have verified I have power at the fuse.
As far as I can tell the fans are wired through the radiator sensor to the pwr source.
I want to test the radiator sensor. With ignition and A/C on should I be able to short the wires at the switch and activate the fans? I tried that with no result but I'm a real electrical dummy so need some direction

Mrmerlin

IIRC you should be able to run the fans with the wires at the switch at the bottom of the driverside front of the radiator touched together, you may also have to push the hood switch down to complete the circuit

Charley B

Thanks Stan, no hood safety sw. on this one. I'll try bypassing the sensor again.

Charley B

There is definately no power at the temp. switch with ignition and A/C on.

IcemanG17

Sounds like the temp sender died...... where is the ground that completes the circuit?

Mrmerlin

check the fuses

pmooradian

Go back to the fuses. If the fans don't run when you touch the leads at the radiator sensor together with the ignition on, no power is getting to the sensor and therefore no power is getting to the fans. All the sensor does is complete the circuit when the radiator gets hot enough. This is the same setup as the stock auxillary fan. The fans should run when the leads are touched together. If you don't have 12V at the positive lead running to the sensor, backtrack to the fuse box. If you can't get it to work, call me or bring the car by. I'll be home most of this week.

Charley B

The fans run when I bridge the hot lead to the jumper post so I assume that eliminates the grounds as an issue.


I checked and shined Fuse #16 "Aux. cooling fan for air conditioning". The only other fan fuse is #17 "Fresh air fan" which I assumed was the blower fan. Nez paux?

There is a relay labeled "Blower fan for additional air con. cooling". Again I assumed that was for the HVAC fan.?

WallyP

Page 97-137 in the Workshop Manual shows this circuit...

Relay XVIII, "Cooling Fan Relay, AC" would seem to be the most likely problem.

Charley B

Thanks Wally, I'll pull it up.

Charley B

So it looks like a bridge between #30 and #87 of Relay XVIII should run the fan, and if so, the relay is bad. Do I have that right?

IcemanG17

If you jumper the relay and the fans run...bingo you found it!!

dr bob

To keep things in proper electrical perspective, consider that you have two S4 fans running on the relay and wiring intended to run one smaller fan. On the S4+ cars, the factory saw fit to have a separate power feeder for each fan motor directly from the battery to the dedicated fuses (one for each motor...) in the CE panel, to the fan amplifier unit on the front apron which contains two independent channels, obe for each motor. Your pre-S4 car has one circuit for one fan originally, now feeding two fans in parallel. Conclusion: It's not too surprising that the relay gave up. It wouldn't be too surprising if some related wiring gave up too. Consider dedicated feeders, fuses and relays for your S4+ fans as a possible solution.

Charley B

I see your point, although I thought the duel system on the S4 was more about having the ability to control the fans seperately for on/off at different times and different speeds for each fan depending on several circumstances; as opposed to just insuring the robustness of the circuit.

This sep up has about 25,000 miles and five years on it so, of course, I'm hoping it is just a 35 year old relay giving up the ghost.

dr bob

Charley-- At the very least, find one of the 40amp rated relays to install. That may give you a little extra life. The S4 fans are designed to operate at part load under almost all conditions. They see full load under high ambient/high engine load condition, and when the car is not moving fast enough to get a natural draft. These are all contributory to elevated coolant temp, which is what the fan conntroller really looks at. The fans will run at full speed when the AC system is activated. Meanwhile, using these fans with the early tempswitch and relay type contrl means that the fans are at full load or off, depending on coolant temp or AC use. Temp rises enough to close the switch, fans come on at full speed until the coolant temp drops enough for the switch to open the relay. Depending on actual load, the duty cycle for the fans and relay may be quite short in low-load winter driving, to quite long in hot weather driving or with the AC on.

You can do a little sleuthing if you want, looking to find out if the new relay and wiring are up to the task. Just use your voltmeter to measure the voltage at the jump-start terminal and at the fans, and look at the difference while the fans are running. Any voltage drop is caused by resistance in the wirng, relay or connections. Under fan load that resistance translates to heat. If that resistance (and the related heating) is distributed over the whole system, perhaps there will be no places in that circuit where the specific heating is great enough to melt insulation or cause a fire. If the high resistance is localized in a single component, a connection or even just a short section of wire, the specific heating of that part or section will go way up, elevating the chances of failure or possibly a fire. Generally, fuses are the weakest link in the circuit and sometimes manage to sacrifice themselves before a more obscure, critical, or more expensive component is damaged. Fig Newton's third law of electrical reciprocity teaches us that the critical, expensive, important components too often fail first, protecting the fuse. Point to this is that the original system was designed just adequately for the single fan motor installed. Running two motors puts at least twice the load on that original wiring and components. So far, you haven't had a total meltdown failure. But you have had a warning, be it a failed original relay or something else that failed in the circuit. The circuit is overloaded. Put a new relay in, and you'll soon discover the next "weakest link". I wonder what that will be. It won't be the fuse, because that would have failed before. Or possibly the fuse has been "up-rated" because it warned someone already. 16A replaced with a 25a or 30a fuse? Wire sizes upgraded to match? The wires and the fuseholders will likely be the next things to melt. Good thing there's no other wiring nearby, wiring that might suffer if there's a fan circuit meltdown.

I hope you are getting the idea here. Think about dedicated wiring, fuses, and relays suitable for the duty. Simple stuff, right? It is if you do it before the other wiring melts.