C5 Allroad Cooling Fans only coming on for HVAC

[RyanB]

Wondering if anyone can help me figure out what I'm missing...

What has been done so far:

• Replaced Fan Control Module J293 and power wiring (was severly burnt out)
• Replaced Electrical coolant fan (was dead)
• Replaced fan switch in lower radiator hose and coolant sensor in rear crossover pipe
• Replaced 60A fuse S42 in slot 19 under dash
• Have been able to jumper pins 1 & 2, 3 & 4 at points in the past to get fans to come on but can't seem to now EDIT: jumping the pins works fine with engine running.
• Direct jumping the fans does turn them on high
• So I checked the wiring continuity/resistance from fan switch connector to 14 pin connector in front of power steering reservoir and from there to FCM and from fan switch to FCM. Everything has continuity/ground. Resistance at 7.5 ohms.
• EDIT: I think I have gotten an intermittent code from the HVAC controller for the ambient temperature sensor. Display has been accurate though. Could this possibly be it?

2003 Allroad Coolant Fan Wiring Diagram.jpg

Thanks,
Ryan

[RyanB]

This really seems to be something with the coolant fan thermal switch. I'm running engine until lower radiator hose gets really hot like the upper. Radiator gets hot from driver side to passenger side during the warm up, so I believe coolant is flowing. I tried another switch that was either the existing one or one I pulled from junkyard, both of those tested at 95°C on temp with boiling water. No continuity on Pins 1-2 or 3-4. I was able to test the new one I just took out outside of the car with a heat gun and was able to get continuity from both 1-2 and 3-4. This is starting to drive me crazy!

[neilthewheel]

With all the stuff you have replaced, running with pins shorted, and that last switch you mentioned switching, you should be good.
The fans on our cars are kinda their own separate system so no ac temp is going to affect it, only the ac request.

Keep in mind that the coolant temp you see on vcds is hot coolant out of the motor, the switch sees cooled coolant out of the rad.
Dont make the mistake of thinking the fans should be on when vcds says 95. The coolant out of the rad is going to be quite a bit cooler than that.

[RyanB]

Thank you. That's what I've gathered. However I've gotten the car warm enough that the bottom hose and radiator near it are very hot to the touch. Temps high enough that the coolant starts boiling and overflowing (115°C-125°C).

In the process of doing a coolant flush now. Temps stayed cooler but we also finally got a 70°F day instead of 90°F+. Of course now that I'm using this vacuum filling tool it's showing a leak and it sounds like it's coming from under the intake (after-run pump and/or hoses). FML.

[neilthewheel]

Sounds like you got a doosy then. What you describe above sounds like fans should be working.
After run aint no thang, but you prob want to take the mani off if replacing or deleting (1" PEX 90 for home depot. Grab 2, one for the glovebox in case of heater core fkry).
It can be done with mani on, but good fkn luck getting the hoses off the hardlines without trashing them and having to shell out bucks. I swear they painted those fkn things with self vulcanizing paint

I think my next vector of attack might be ghetto-fabbing 2 temporary toggle switches in place of the lower rad hose switch to see if you can get it run properly by manually babysitting it.
If that dont work, super high quality laser guided temp gun from harbor fright on the rad in different places to see if it is flowing and doing its job. Can be had for like 9.99
Other places to consider afterward might be plastic water pump (I know its PPS and not plastic, but I aint buying a certain vendors propaganda vid, plastic is fkn plastic lol), or Tstat.

[RyanB]

So of course after getting the manifold off enough to get at the pump, I tried pulling a vacuum on the system one more time to double check the source of the leak sound. And of course the leak isn't nearly as bad. Perhaps I had the tool not properly seated to the reservoir. Anyway it will pull vacuum to -24psi and maybe drop .5psi in 20 seconds. The small bent lines going immediately in and out of the pump have not collapsed from vacuum, but I assume the bends make them too stiff right there to do so. I don't even really see much coolant in the valley (just some other sludge). Not sure if I should even replace the pump though I do have another one on the way. I was just making sure it wasn't one of the hoses.

Does anyone know what sort of vacuum the system should be holding and for how long?

[RyanB]

Sounds like you got a doosy then. What you describe above sounds like fans should be working.
After run aint no thang, but you prob want to take the mani off if replacing or deleting (1" PEX 90 for home depot. Grab 2, one for the glovebox in case of heater core fkry).
It can be done with mani on, but good fkn luck getting the hoses off the hardlines without trashing them and having to shell out bucks. I swear they painted those fkn things with self vulcanizing paint

I think my next vector of attack might be ghetto-fabbing 2 temporary toggle switches in place of the lower rad hose switch to see if you can get it run properly by manually babysitting it.
If that dont work, super high quality laser guided temp gun from harbor fright on the rad in different places to see if it is flowing and doing its job. Can be had for like 9.99
Other places to consider afterward might be plastic water pump (I know its PPS and not plastic, but I aint buying a certain vendors propaganda vid, plastic is fkn plastic lol), or Tstat.

Yeah, I'm starting to consider looking at the thermostat. I just hate having to eff around with the timing belt. Guess that will teach me not to do a timing belt job without a proper cooling system flush first.

I also thought about a manual switch set and also the temp gun. I did feel the radiator from driver to passenger as car warmed up and it did get hot in that direction.

[RyanB]

I did manage to remove and checkout the thermostat yesterday. Opened up fine in boiling water. I believe I had it oriented properly with the bleed hole up and support bar horizontal and facing out (springs into the engine).

The Prestone flush product I used has actually made the inside of the block look a lot better too. Going to get everything back together and flush once more with distilled water.

Fingers crossed that a good vacuum filling solves any issues.

[RyanB]

So I've been on epic cooling system journey. Got all 5 coolant pipe O-rings replaced and now it holds a nice perfect -25psi vacuum. Vacuum filled with distilled water as part of the flush clean up. Still the same results in that the auxiliary fan thermal switch (F18/F54) is not coming on. Not really sure what to do at this point.

[RyanB]

Having a little bit of a breakthrough. Got yet another sensor (Meyle, new) and the fans do seem to be coming on ow briefly around 114°C+. I know that's not the temp the switch is seeing after the radiator, but does that seem to be about the right temp for them to come on idling in the garage? Been idling for like an hour. I guess a 20°C drop through the radiator seems about right. Guess I just need to test drive it for real now. Going to pre-run some wiring for a manual switch just in case...