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Radiator cooling fan stays on low
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Californio
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PostPosted: Mon Jan 01, 2024 12:19 pm    Post subject: Radiator cooling fan stays on low Reply with quote

Hi all, and Happy New Year...

My radiator fan is staying on. This started yesterday while we left the van for a hike. After an hour or so the starting battery was completely drained.

The AC is off. Controls don't make a difference.

The fan stops running when I pull the plug on the thermoswitch on the radiator.

Any preliminary ideas on what this could be? Buslab is open tomorrow so I think I can get a new thermoswitch there, but my understanding is that these rarely fail in a closed position.

Is there an easy way to disable the AC circuit temporarily to see if it's that?


Thanks for any advice...
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PostPosted: Mon Jan 01, 2024 12:28 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

From what I've read here on TheSamba, the AC system switches the fan on at high speed, not low. That being said, I don't think the problem is in the AC circuit. I would simply take a multimeter and check the switch for continuity. If the van is cold, the switch should not have continuity.

Hans
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PostPosted: Mon Jan 01, 2024 12:32 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Will do, I should have thought of that!
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Californio
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PostPosted: Mon Jan 01, 2024 12:37 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Stone cold the outer two contacts show continuity. So the switch is bad.

Thanks so much, will post results after I replace it!
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MarkWard
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PostPosted: Mon Jan 01, 2024 1:59 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Good diagnosing. Pretty sure factory AC turned the radiator fan on low. When pressure hit the target radiator fan would be on medium. If the radiator fan switch went to high speed, ac compressor shuts off. I post this for someone in the future is using the search feature. On a factory AC van, the radiator temp switch is medium and high. It’s actually a 3 speed radiator fan.
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ALIKA T3
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PostPosted: Mon Jan 01, 2024 8:00 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

MarkWard wrote:
Good diagnosing. Pretty sure factory AC turned the radiator fan on low. When pressure hit the target radiator fan would be on medium. If the radiator fan switch went to high speed, ac compressor shuts off. I post this for someone in the future is using the search feature. On a factory AC van, the radiator temp switch is medium and high. It’s actually a 3 speed radiator fan.


I think AC turns medium speed (speed 2) via relay 53, regulated by the resistor.
Speed 1 and 3 are triggered by the thermoswitch.
Speed 1 is regulated by the resistor.
Speed 3 is full on high speed.
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PostPosted: Tue Jan 02, 2024 12:21 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

@Alika I'm looking at page 97.141 I may have misremembered. Looking the diagram now, The 95C degree rad temp switch sends power to spot 2 of the radiator fan resistor or radiator low speed. When the AC relay is energized, power is also sent to the same pin on the radiator fan resistor or low speed.

When the AC pressure builds to 15 bar, power is sent to radiator fan relay in position 5 of the fusebox. That relay energizes and sends power to position 1 on the radiator fan resistor or medum speed.

Lastly, when the radiator fan switch activates at 102C, it energizes the 3rd stage radiator fan relay. This relay sends power directly to the radiator fan bypassing the resistor completely and running the radiator fan on high. At the same time the same relay energizes the compressor clutch relay and shuts off the ac compressor.
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Californio
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PostPosted: Tue Jan 02, 2024 6:22 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

I replaced the thermoswitch with one from Buslab (which by the way is a great place to get parts in the Bay Area) and fan operation is back to normal. It cycles on when temp gauge is about 3/4 up.

A couple of observations: These switches can fail intermittently. Before replacing mine I plugged the old one back in and it worked, ie. fan was off at low temperature. I unplugged and did it again later and it was bad, fan on. Also, I noticed in about the last year that it seemed to be kicking on too low after just a few minutes in traffic and with the gauge just barely above where it usually sits.

A question. Could a failing thermoswitch possibly cause a low-level current drain on the starter battery? Especially since it's on the constantly-powered circuit? Just wondering if that could be the cause of my drain, and as far as I can see, pulling the fuses wouldn't catch this. I'll observe overnight the next few days and see if there's a difference.

Thanks for the help so far.
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E1
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PostPosted: Tue Jan 02, 2024 6:41 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Californio, for what it’s worth our fans have almost always come on just a tiny bit above half-gauge.

This could mean your thermostat’s not opening until hotter than designed, or for whatever other reason your radiator’s not getting hot enough to trigger the fan until your coolant temperature in the block is higher than it should be.
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PostPosted: Tue Jan 02, 2024 8:37 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Hmm, food for thought...I think I need to get an infrared thermometer in the near future...I've always thought of the temp gauges as being guesstimates like the gas gauge but worth checking.

My test was just to let it sit there idling in the driveway for 20 minutes, nothing too sophisticated.
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PostPosted: Tue Jan 02, 2024 8:47 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

If you do get one, and have a stock plastic tank, I normally see about 160 to 180 on a normal drive at full-temp on a warm to hot day — when pulling over and taking an immediate temp through the license plate door on the compression tank.

They can be inaccurate, I test my skin before every use to look for variations. Normally shows about 95.
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ALIKA T3
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PostPosted: Tue Jan 02, 2024 10:09 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

MarkWard wrote:
@Alika I'm looking at page 97.141 I may have misremembered. Looking the diagram now, The 95C degree rad temp switch sends power to spot 2 of the radiator fan resistor or radiator low speed.
I agree
When the AC relay is energized, power is also sent to the same pin on the radiator fan resistor or low speed.
I don't see this logic in the diagram, so I think you're onto something that can help me clarify my foggy interpretation then. Which relay is that ? (AC clutch?) and what track number please?

When the AC pressure builds to 15 bar, power is sent to radiator fan relay in position 5 of the fusebox. That relay energizes and sends power to position 1 on the radiator fan resistor or medium speed. I thought medium speed was running all the time, electrically turned on by the AC knob switch ? Where is this track for the pressure related activation?

Lastly, when the radiator fan switch activates at 102C, it energizes the 3rd stage radiator fan relay. This relay sends power directly to the radiator fan bypassing the resistor completely and running the radiator fan on high. At the same time the same relay energizes the compressor clutch relay and shuts off the ac compressor.
Agreed


Hi Mark!

Looks like you understand the diagram better than I do, and I'd like to get to the bottom of this bc I have an issue on my SmallCar AC I have never been able to figure out, and I feel like you have the key to my issue somehow.
I've put some answers to your text in blue
My system is running a 1986> fan system in a 1985 van, I swapped over the entire harness, and made the SCP AC system running the medium speed for AC which is prolly a mistake now?
Somehow, the radiator thermoswitch engages the compressor clutch even with AC off, it's been killing, I have no idea how it's possible. I know the answer is around the resistor/thermoswitch and trinary switch in my set up, but nobody seems to see it. (I asked on the DIY AC thread before).

Happy new year!

Image may have been reduced in size. Click image to view fullscreen.

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MarkWard
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PostPosted: Wed Jan 03, 2024 5:52 am    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Our 90 had an intermittent radiator fan operation. The problem ended up being a bad internal connection of the fuse box for fuse 1. I ended up moving that connection off of the fuse box and using a circuit breaker. Probing the fuse with my test light is how I stumbled across it.

@Alika, I need to drink some coffee and get to my computer to think about your observations in blue. Lt. Blue Vanagon
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PostPosted: Wed Jan 03, 2024 11:48 am    Post subject: Re: Radiator cooling fan stays on low Reply with quote

@Alika, the AC should operate the radiator fan on low and medium based on your diagram. Low when ac is turned on and medium when the AC pressure switch current track 14 is activated.

The AC compressor clutch relay tracks 15 through 17 is a normally closed relay. If it sees power from the high temp fan thermo switch pin 1 above track 18, the AC relay opens and the clutch is disabled till the fan shuts off of high.

I have a vintage air unit in our 82. I believe its similar to the Small Car. I transplanted a 450W radiator fan, harness and speed resistor from a 90, but the other wiring is slightly custom, but using the Factory air wiring as a template.

The Vintage air dryer has a trinary pressure switch. Its similar to what the factory had designed in but all in one. The problem was getting the AC radiator fan requirements and the cooling system electrical to work together. My solution was to use the radiator switch to complete grounds for the relays instead. The Trinary switch on the dryer was also wired to switch grounds to the same relays. I've had no feedback problems, but realize now, I missed something, but I think my design was right for me. I am using 40amp Bosch fog light relays. I like that they have two output leads and brackets for easy mounting

On a 3 speed radiator fan, low speed is about the same as dog breath compared to medium. It was good to have it come on low as soon as the AC started, but the AC is wired to operate the medium speed of the radiator once the pressure is high enough from the Trinary.

I wanted the radiator thermal switch to run the fan on medium, not low. It comes on so rarely with the TDI from heat, that if it is on, its because we got a little warm and I want it to cool down. Since we travel mostly with the AC on, the radiator fan is on medium most of the time from high side pressure.

The high speed radiator fan, was more a fail safe for if the low temp part of the switch failed. Or extreme engine heat on a slow climb where the flow across the radiator is not sufficient. I believe the engineers felt that when the Radiator fan is on high, it would be better to remove the heat from the condensor while the fan was on high. Thats why they added the compressor clutch relay to shut the compressor off when the radiator fan is on high. I opted to not include that feature with my custom wiring.

As far as the temp gauge readings to others. I've seen a lot of gauges over the years and they all have their own personalities. If its repeatable at normal operating, then you'll see if something changes. When I work on a cooling system. A fast idle sitting still is adequate to test coolant circulation and the radiator fan circuit. I set the rpm around 2000 and wait. Eventually radiator fan should cycle on and cycle off. A short period of the radiator fan running is a good indication the radiator is up to the task and thermostat is requlating temp. You'll barely see the temp drop on the vanagon gauge. Its maybe 10 -15 degrees. If the radiator fan clicks on and stays on or stays on for a long time, that indicates a problem. If the radiator fan does not come on, you have a circulation problem or an electrical problem. Hope that helps.

Alika you are always free to PM me if you'd like to work out a specific thing. Mark
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PostPosted: Wed Jan 03, 2024 11:54 am    Post subject: Re: Radiator cooling fan stays on low Reply with quote

Quote:
I don't see this logic in the diagram, so I think you're onto something that can help me clarify my foggy interpretation then. Which relay is that ? (AC clutch?) and what track number please?


Sorry missed this. Its hard to see your diagram and post at the same time. The AC high pressure switch sends power to H6 on the fuesbox. Current track 14. There is an internal path in the fusebox to relay position 5 on track 23. When power is applied to H6, 2nd speed relay in energized on pin 86. You can see the relay coil is grounded at ground 10 track 23. Does that help? Mark
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PostPosted: Thu Jan 04, 2024 5:50 pm    Post subject: Re: Radiator cooling fan stays on low Reply with quote

MarkWard wrote:
Quote:
I don't see this logic in the diagram, so I think you're onto something that can help me clarify my foggy interpretation then. Which relay is that ? (AC clutch?) and what track number please?


Sorry missed this. Its hard to see your diagram and post at the same time. The AC high pressure switch sends power to H6 on the fuesbox. Current track 14. There is an internal path in the fusebox to relay position 5 on track 23. When power is applied to H6, 2nd speed relay in energized on pin 86. You can see the relay coil is grounded at ground 10 track 23. Does that help? Mark


Thank you Mark!

I'm going to sit down calmly when the baby gives me a minute, and look at my notes to see what I did and what should be corrected on the SCP wiring side.
I know the VW side of the radiator fan wiring is correct as it is unmodified and rather basic function.

I'll hit you up next in PM, thank you for offering!

Aloha Razz
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