Cooling fan issue (bad ground)
 

I originally created the below thread under the "new member" section since I was limited to where at the time (which is odd since I am a 10 year member).

https://www.rx7club.com/showthread.p...0#post11025340

One member suggested the thermoswitch which I am replacing regardless but since I cannot get fans to engage when turning the AC on, I suspect that there may be more going on here. Currently if I ground at the fan plug, the fans engage but only with the AC on and not at temp.

Original post:
"Hello all, my 3rd gen has overheating issues and through a process of elimination as it turns out it is a bad ground feeding the fans but I am unsure where to go from here.

Here is what I have determined,
- When connecting the fans directly to power, they come on.
- When I manually ground the fan to the battery and turn on the AC, they come on. They will not engage on their own though even at 230F.

So it appears that there is a grounding issue further upstream. I was told to check the ground on the coolant temperature module or to the temperature switch. Unfortunately those all seem pretty buried in the engine so I am unaware where to trace this back to.

Can anyone suggest where to go from here or if there is a way to just bypass and have the fans come on (preferably at a lower temp than stock) automatically based temperature without having to trace all this back through the relays? I also want to avoid having to manually turn the fans on based on running temp. Could this be caused by a relay? I was only able to pinpoint one relay for the fans as clearly marked on the box but I hear there are a total of three? If there are any images anyone can point me to where to look for these it would also be appreciated."

Follow up post,
"After scouring these forums for every cooling fan issue/suggestions I could find, I went through everything looking for a bad ground. Pulled the intercooler out, got to the wire harnesses and checked for any broken wires, which I could find none. I pulled all 4 relays out and tested them all on a volt tester and they all passed.

As I was putting everything back together, I noticed a blue plug that was dangling tucked down behind the water pump. I was not able to find anything that it plugs into, in the off chance it was related to my fans not engaging I was hoping someone could tell me where to plug it in.

I also found some posts suggesting jumpering a couple points in the diag box as well as a few other places as a process of elimination. If I cannot find the break, is there any way to rig this so it still comes on at temp or is my only other option a manual switch? "

Thanks as always!

I'm curious....how do you know the engine is at 230F?

The ground points for the fans are attached. Numbers 1 and 2 on the diagram. You should get a wiring diagram....it'll make hunting this down much easier.

That blue plug is for the EGR switch on California cars, it's fine that it's not plugged in, that's normal.

How did you test the fan relays? I have seen relays go bad. You can unplug and jumper the connectors to each relay to test if the circuit is good. If the fans kick on with a jumper wire, the wiring is OK as far as powering the fans, it could be an input.

Read my thread on fan control, that will tell you how the fan system is supposed to work.

Dale

I have a digital temp gauge in the car, I knew it should have come on at 221F but let it climb a bit higher just to make sure.

I do have a wiring diagram but I must admit, it is hard to decipher. Most of my reference has been from my 1100+ page rx7 shop manual. I will take a closer look at the diagram you sent me, it may reveal where my bad ground is.

I used a volt tester and jumpered the points based on what it said in my shop manual. They all passed resistance tests.

So far if I connect the fans to the battery directly, they both come on. If I ground to the battery from the back of the fan plug's ground, they will only engage when I turn on the AC.

Thanks so much for revealing what the plug is, one more thing I can cross off as a suspect. I will take a look at your thread on fan control and see if I can make any sense of it.

When you say the "if the fans kick on with a jumper, they are ok" doesn't that just prove that it is getting power but not necessarily a ground? I would really like to eliminate a bad wire since a lot of the wiring is next to impossible to get to.

You all rock! Thanks so much for the suggestions!

Here's a good place to look: your ecu ground. Is your ecu unbolted by chance? I know when I was checking my grounds for another unrelated purpose I discovered that upon I bolting my ecu from the frame, effectively un-grounding it, my fans came on!

Hope this helps.
Matt

Study it, read the intro pages a few times, compare the diagrams to the car, and you'll eventually learn how to "use it". It is tricky at first learning what all the symbols and notations mean, but once you learn it, it is a breeze.

Following the diagrams and doing continuity checks for the ground circuits as well as what I would call the relay trigger/control circuits should get you to an answer the fastest.

Wow I will definately have to take a look at this! Thanks for the suggestion.

If not, time to start studying my wiring diagram.

Thanks again all!

Ongoing Cooling fan issue (FOUND bad ground!)
 

Thanks to some of your suggestions, I found the bad ground (see attached pics). The fans now engage when I pop the A/C button.

Unfortunately, they still do not come on at temp. I got the car to 222F and nada. I have been looking at the wiring diagram and it appears the next jump is directly to the fans and the otherside to the side to the relays.

Since I thought I tested the relays (on the relay itself) via ohm resistance. Unfortunately, I had to test them at the pins because I could not get the rubber housing off of them. They all seemed to pass.

Since the fans now come on with AC, any idea's where to go from here? I figure that there was something that torched the fan ground so whatever is upstream form that might be bad.

Any suggestions, comments will be greatly appreciated. I can't give up and take it to a mechanic at this point, I am too close!

If the ground is now good (it looks TERRIBLE btw) you should be able to jumper each relay plug and get the fans to come on. If that's the case then the fans and their wiring is good, time to test other fan inputs.

Dale

So can I get a little more info on testing the relays? First, I am not testing the relays themselves? Rather jumpering what they plug into? Is this done with car running at temp? Or just with ignition on? Also, am I just jumpering the ground or do I need both pos and neg from the battery?

Also note that I have not tested or gotten to the fan thermoswitch yet. I do plan on replacing with the thermoswitch mod as previously suggested. This way I don't have to reach 221 to even know if it is working correctly.

What symptom would I notice if the fan thermoswitch was just bad? It seems rather difficult to get to the thermoswitch, i would rather tackle that after I fix the fans.

Getting close thanks to you all!

Don't mean to hijack the thread, but I have a really similar problem with my car. The A/C switch doesn't turn the fans on either.

The relays works fine when I manually give it a 12V input. Also the fans turn on fine when I jumper relay No.1 from the harness. The strange thing is that the A/C switch input to the relay is only reading around 6V when I measure the harness plug. I suspect that the relay isn't getting enough voltage to turn on.

Maybe through your investigation, you might has some insight into what might be wrong with mine. I don't have a clue as to how I can track down this voltage drop or bad ground or whatever it is.

Just came across your reply but unfortunately I wasn't able to completely fix the issue. If you scroll up, you may notice the fried connector that I found when removing the front bumper. After fixing the plug, the fans come on when hitting the AC button but not on their own. Still better than I was since I can keep the car from overheating by hitting the AC button.

I am at my wits end with this electrical issue and I am either going to sell it as is or invest in a temp sensor bypass. I only wish I could find a Rx7 mechanic in my area without having to tow it 100+ miles.