Another radiator fan T/S thread...No voltage at sensor SOLVED

[Ben Root]

My radiator cooling fan is not kicking on. Definitely not the high speed, but I'm not sure about low speed either.

I tried jumpering the wires at the thermocouple (at the radiator )and got nothing. But I also tried measuring voltage on those three leads (to chassis) and got nothing either. It seems to me there should be 12V there (on at least one of those leads) no matter what, right? That circuit is always hot...because the fan can run after the key is off. I did check fuse #1 (30A) and fuse #5 (read something somwhere) and have continuity across the fuses.

The van is a '91, with A/C (but that was disconnected years ago when the Subi motor was installed...fan has worked fine for decades until recently). Van stays right on temp, unless I'm stopped in traffic in the heat. Then the high-speed doesn't kick on like it should, and I get a pegged gauge and blinking LED.

Most of the discussion online involve jumpering across the thermocouple: if that kicks the fan on then the thermocouple is bad. if it doesn't then it's downstream (fan, or wiring to, or ground). But I'm not getting voltage at the thermocouple...so I'm not ready to blame downstream yet.

Can anyone shed some light for me?

[Howesight]

The device you refer to is a thermo-switch. A thermocouple is a different animal.

Here is what to check:

1. There is a 50 amp fusible link behind the dash which is visible if you pull out the left (driver) side dash vent. Here is a pic on my rig with the dash removed:

The yellow arrow points to the fusible link.

2. The red arrow points to the relay that drives the highest rad fan speed.

3. Behind the driver side headlight is the resistor set (two resistors in one) that control the lowest rad fan speed and the medium rad fan speed. Below is a pic of where that resistor is located. Mine is not the Vanagon unit and I substituted a resistor from a Eurovan. The stock resistor is fine and GoWesty and other vendors sell them.

4. The rad fan switch can fail.

5. Equally common is the problem that the radiator gets clogged to the point that coolant flow to the thermo-switch is not adequate to close the switch inside. In that case, a new rad is required.
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'86 Syncro Westy SVX

[crazyvwvanman]

You must have 12v power at the radiator temp switch wire for either low or high speed to work.

Find and fix that first. The red/white wire should be power from fuse #1 to the temp switch.

Forget high speed for now, low speed should be all that is needed for extended idling without A/C on.

Note that the wire colors shown at the switch are wrong in the Bentley A/C diagram but the A/C diagrams are what you should use for the fan wiring since your van came with factory air.

Mark

[Ben Root]

Thanks for the additional info on the system. It helps me understand. Of course you are right that I needed to chase source voltage first. I tricked myself because I couldn't get my meter probes into the fuse 1 slots far enough to detect voltage. Finally I stuck a spade connector in there and then touched the probe to the connector...voila...there actually was voltage at the fuse panel. So then I decided to check the fuse itself again, and what-do-you-know the fuse was blown (or maybe just broken). The deal was that one of the spade ends on the fuse was loose in the fuse plastic caseing, and would wiggle. In some positions I measured continuity across the fuse, in other positions not. It was noticing this loose wiggling that got me to recheck continuity. Replacing the fuse seemed to fix everything...duh. I did the jumper test at the thermocouple leads and was able to get both low and high speeds to work. Then I plugged it in and warmed up the van enough to get low speed to work. I didn't want to try to force overheating enough to be sure that the thermocouple would trigger the high speed fan...but I'll keep my eye on that scenario out on the road. Thanks again.

[djkeev]

[Sodo]