Basic/beginner guide for car wiring? Specifically, relay related.
July 17, 2017 9:01 AM   Subscribe

I drive a 2007 town and country limited (3.8). I've been getting under the hood myself with the help of youtube to check smaller things when my mechanic friends aren't able to help. We recently noticed that the fans don't come on unless hooked directly to the battery. The air has no refrigerant due to a leak that I'm also hoping to fix soon. I've changed the coolant temp sensor (no change). Changed the fuse (no change). Checked relay. This is where I'm stuck. I need a guide to wiring and don't know where to look or what's good for my situation.

I attached the new relay and nothing has changed. I checked it with a continuity tester and saw that when hooked to battery negative wires 123 come on. On positive 1 comes on. Nothing else happens and there are no codes showing on the van. As you can probably tell, I'm super new at this so I don't know what it all means and I'm not yet finding sources that can give me information in basic terms for this model year. I don't know where to go from here.

One mechanic wants to hot wire them so they work but I'm not a fan of the idea. I'd like to just fix it. Still waiting to hear from the other but would like to at least learn some of this myself. Is there a really basic guide for this type of issue? With diagrams? My car manual doesn't do it for me.

For reference, the thermostat and the spark plugs were recently changed due to overheating/fluctuating temperature issue and a code for the plugs. Since then, it has overheated once and only after sitting in traffic a while. The needle doesn't move as sporadically as it once did, generally stays below the half line. There is an issue where the battery tends to cut off once I'm stopped a while (like in the grocery store) but I think it may be that it needs tightening or new connectors and not necessarily due to overheating. Still researching. It hasn't leaked nearly as much, doesn't require constant coolant (I did add a radiator leak fixer) and it runs better now outside of this fan issue. Just not sure how to fix this fan issue further without a proper guide, site, book, forum.
posted by grablife365 to Travel & Transportation (5 answers total)
There may be a coolant temp sensor AND a temp switch for the fan. So you have replaced the sensor for the temp gauge in the van, but not the thing that switches the fans on or off. That, or the ECU is switching the fans on at a certain temp.

Run through the wiring from the fan to wherever it goes. It will either be switched to earth or (more likely, if a relay is involved) switched power supply to it. Basically, whatever is triggering that relay is not doing so. So it's north of the relay that the issue is - either the temp switch is not working (if it has one) or the ECU is not switching the fan on (odd and unusual) or it can't do so for some reason (either switching control wire is broken or power wire to relay is, or control wire from relay to fans is).

When you say the fans work when hard wired to the battery - have you done this from the relay location? Or direct to the plug on the back of the fans. When you say 'checked the relay' have you tried a different one? Or a new one? Relays can do weird things when they fail. I would have done the following:

Check relay/fuses/connections. Clean anything that looks anything other than shiny and even swap out a fuse/relay to see if it makes a difference.
Put 12V to the fans themselves - this tells you if fans work.
Put 12 to the fan feed at the relay point (take out the relay and check for 12V supply and 'jump' the relay position) - this tells you if the wiring from relay point to fans is good, and can tell you if there is an iffy earth or feed of power to the fans if they don't work at this point. If the fans work fine if you jump the relay it is either the relay itself, or feed to it.
Try a different relay of the same type in the fan position - if it doesn't work, it isn't the relay.
Check wires to the relay supply - You may have 12V at the relay, but an iffy power connection may mean you don't have enough current to run the fans when the relay is triggered.

If you have established that all wiring is good, it is temp switch (if it has one) or ECU/ECU wiring. At which point, on a car that old, I would very much just wire the fans to a switch inside or hard wire them to come on with ignition.
posted by Brockles at 9:29 AM on July 17 [1 favorite]

Chilton/Haynes are the basic guides.

As for the fan control - they are often fairly complicated. You've verified that the relay and the motor work, but there is control logic (analog or digital) on the dash that adjusts speed/damping etc. I'd start at that end and work towards the motor, though this may require disassembly of the dash to get at things.
posted by Pogo_Fuzzybutt at 9:32 AM on July 17

but there is control logic (analog or digital) on the dash that adjusts speed/damping etc.

I understood the question to be about the radiator/engine bay fan. Not the passenger compartment fan.
posted by Brockles at 9:37 AM on July 17

I was confused on that point - the "The air has no refrigerant due to a leak that I'm also hoping to fix soon." made me think he meant the cabin air fan. Since you covered one base, I thought I'd grab the other.
posted by Pogo_Fuzzybutt at 9:52 AM on July 17

Thank you all for the answers.
You may be right about a switch. I remember reading about one but I'm not sure if it's this year. I'll dig there and check.

I did not connect the relay to the battery. I tried, it sparked, I got worried. I'm sure it's supposed to but I didn't continue because I wasn't sure I was doing it correctly. I have red/black jumper wire but needed to find a visual or instructions to figure out if I'm doing it correctly. So, I'll need a tool to check for 12v then jump from there?

I have a brand new relay that I connected to the relay connector/wires. It didn't do anything.

I mentioned the air refrigerant because I was told that could factor into the fans working. Without refrigerant, I wasn't sure if it was hindering the whole thing further.

Thanks again and for the guides!
posted by grablife365 at 10:19 AM on July 17

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