mhr

I am questioning the way the cooling fans behave in my 91 S2. I read through clarks description and mine do not seem to operate the same.

If I turn the ignition key and hit the AC button the fans start to go in what I believe to be High for about 5 second and then they slow down to low for about 5 seconds and then repeat. This continues while the AC is on.

I don't think the low fans are ever triggered on their own. in traffic on a hot day the car will heat up to the second mark on the gauge and then the fans kick in with the same pulsing high/low fan and push the temp back down to the first mark then turn off.

With the AC on the fans pulse and the temp will never get much above the first mark.

Is this the way it is supposed to work and if not how should it work and which part of the system should I be checking first?

Thanks

Mark

Der Treiber

No, that is not normal. It is normal for the fans to go on whenever the a/c button is pushed on. However, the cycling back and forth on five second intervals is not normal. I had a similar problem where my fans were cycling 10 seconds at high, then 3 seconds at low. I checked all the relays first, then found that the wires leading to the fan resistors (these are to the right of the battery compartment on the firewall, somewhat behind the wiper mechanism) were corroded and the insulation was dry and cracked. I stripped them back to good insulation, cut off the corroded wire, put on 2 new layers of heat sink and resoldered new spade lugs. Luckily, there was still enough length on the wires to plug back into the resistors. The fans worked perfectly after that. Not saying this is your problem, but might be a good thing to check.

V2Rocket

im thinking the relay is toast if it cycles like that.

mel_t_vin

This.

BTW, some cars had these resistors located on a bracket mounted to the firewall, inside the cabin, behind the glove box.

mhr

Thanks guess i will be looking into this ASAP.

cruise98

It sounds like the resistors are bad, or the wires near the resistor are burned. Very common issue. Here is one of my old posts about this very issue. Do a search for Fan relay and you will get lots of hits! Start at number 4.


The fans are not dependent on key position and can run at any time. Do they run the battery down? Check out Clarks Garage or use this procedure to narrow down the problem.

During normal operation, and you have the factory rated thermostat, the coolant temperature gauge should read at or near the lower white line (80 degrees C) and will creep up to the mid-point between the upper and lower white lines when sitting still in traffic. The upper white line represents 100 degrees C. If the temperature normally runs above the mid-point, you need to investigate immediately.

There are several temperature ratings of the thermo switches, so it is hard to say at what point they should turn on for your car. If they are not both running at high speed when the temperature is above 90, you might have a problem.

The fans are controlled by the cooling fan relay which is in turn controlled by the thermo switch, and the a/c system. Whenever they are closed, both fans should run at the same speed at the same time. If only one is working or you only get high speed operation, there is a problem.

You should always have power available to the relay, so the fans can run at any time. Remove the cooling fan relay. It is the large rectangular silver relay in the back of the panel. Check the diagram on the fuse panel cover for the exact location. Most of the following checks can be made at the fuse panel . You will need a bright light to see the markings on the fuse panel.

1. In the Bosch world, a terminal designation of “30” means it is un-switched battery voltage. Check for voltage at positions 30 M1 and 30 M2. You should get 12v + at both positions. If no voltage, check the fuses first, then wiring from the battery, the connections to the fuse panel, and the fuse panel itself. You will have to pull the fuse panel up, but disconnect the battery before messing around under the fuse panel.

2. Check for continuity between ground and the temp switch positions "TS" and "TF" on the fuse panel. If you have continuity, the thermo switch is calling for fan operation. If the car is cold, the thermo switch is bad.

3. Disconnect the thermo switch connector at the radiator, and jumper terminals 2-3, you should have continuity at TS. Jumper terminals 1-3, and you should have continuity at TF.

4. Fabricate a jumper wire with flat blade connectors on each end, and a 20a fuse in the middle.

5. Connect the jumper between M1 30 to M1, the drivers fan should run at high speed. If the fan does not run, check for voltage in the connector at the fan motor, if you have voltage but the fan does not run, replace the fan motor.

6. Check the passenger fan by connecting the jumper between M2 30 and M2, the passenger fan should run at high speed. If not, the same drill.

7. Next connect the jumper between M1 30 and V1, the drivers fan should run at low speed. If not the resistor or wiring is bad. Check for voltage at the radiator fan connector and then check the resistance across the resistor.

8. Next connect the jumper between M2 30 and V2, the passenger fan should run at low speed. If it does not run, check the wiring and resistor.

If the car is still running hot and the fans are working properly, you have other issues, like a clogged radiator, water pump failing, air bubbles, bad thermostat, or a bad head gasket.

The other positions on the fan relay are:

X = battery power to the logic board in the relay
31 = Ground for the logic board in the relay
AC = AC freeze protection switch

mhr

Great detail thanks!

Will report back

SpeedyC2

My bet is for the wires leading to resistors on the firewall as well. My S2 had identical behavior when I first picked it up, and some electrical tape to cover the old, exposed wire, followed by contact cleaner and dielectric paste on both ends of the spade connectors and the fans act as they should.

I check back to them occasionally and clean and reapply dielectric. All is well. (Knock on wood!)

mhr

ugly…get the soldering iron out.

jhowell371

Nasty looking, I better check mine

mhr

Looks like problem solved. Did not get a chance to run it and see what happens when she heats up but now I put the ac switch on and low fans come on and no pulsing.

After:

mhr

Crap I think I see some rust in the photo bottom right. Have to check that out possibly throw on some POR-15 before it becomes a problem.

mel_t_vin

Therein...lies the problem. Glad you got it sorted out.

So, for folks that have looked at their resistors, does anyone else have two smaller [penny sized] circular resistors, one wired in series with each larger resistor, on their bracket? I do, and they're mounted in the empty holes on MHR's bracket.

Curious...

SpeedyC2

Nice work!

cruise98

I love blue electrical painters tape. That is a nice touch! Nice job on the repair. The resistors put out a lot of heat and a better heat sink would help as well.

mel_t_vin: I would guess that you have modified setup. If the resistance is correct, there is no harm.