Syncro - Radiator Fan - Thermo Switch

[jeepboy_90]

Vehicle: 1998 Syncro Doka - 2.1/manual/no A/C

Issue: No low speed radiator fan, does not kick on at any time.

While driving the other day, it was a little warmer weather than we normally get the high speed fan kicked in while we waited in traffic. But I hadn't heard the low speed kick on.

First I checked fuses and relays (all good), then I checked the resistor behind the headlight (dual resistor with two wires) it appears to be in good condition and as I understand slows the fan down making the "low speed". I removed the connection at the thermo switch and tested by jumping the wires. When jumping it I get "high speed" and "low speed" by making the different combinations.

This makes me think that the resistor is working, as it reduces the fans output providing a low speed, giving me the thermo switch as the culprit.

I can't not find a test procedure for the thermo switch. Only the cut-in and cut-out temps in the Bentley Manual (19.12).

Can any one provide the test procedure or have any ideas on what I might be missing.

Thank you
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1988 Syncro Doka
1986 Syncro Tintop
1971 Haflinger LHD
1973 Haflinger RHD

[MarkWard]

Your testing indicates the radiator fan switch has failed on the low speed circuit. The test would be with an ohm meter.

I’m also assuming the coolant is circulating since high speed works.
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[jeepboy_90]

Yes, coolant is circulating.

To test, I could let warm up and see if the switch is triggered, while reading the resistance?
_________________
1988 Syncro Doka
1986 Syncro Tintop
1971 Haflinger LHD
1973 Haflinger RHD

[MarkWard]

[crazyvwvanman]

I helped a friend with this problem this summer. His 90s fan came on high speed a lot but never low first. He had recently taken it to a "Vanagon specialist" shop for overheating issues and this is how it came back.

I live up a hill and when he showed up I could hear his high fan as he approached. Then it shut off without dropping down to low, and as he idled high came back on.
I told him it was likely the switch but he said no since the shop had installed a new one.

I put a new Wahler 2.1 version switch in anyway. Low then came on when expected and cycled on and off during long idles.

The new switch we took out wasn't just bad, it was also the wrong one, an Audi version 75 degree switch, in this case made by a discount parts company that starts with an M.
Vanagons with factory A/C are designed to disable the A/C compressor whenever the radiator temp switch triggers high speed fan. Using a switch that triggers at much lower temps means the A/C may become nearly useless on the hottest days when you need it most.

Mark

[Wildthings]

Fan switches fail, in my ~600,000 miles of Vanagon ownership, I have replaced at least 5 of them on my own rigs and keep jumper wires in the glove boxes so I can activate the fans should a switch fail.

[TopaTopa]

Wildthings and group- comment about failed fan switches caught my eye. My fan switch was working fine but in following some early TenCent advice decided to replace it as preventive. Put in a new German Wahler, no low speed fan [edit- high speed fan worked]. Put back old one, low speed fan works fine. Appears bad switch? Has this happened to anyone with a Wahler? I want to get a replacement Wahler but now leery.