Fan coming on all the time, is this common??

[sgreiner1011]

I have a 94 RT and ever since I had it, the fan keeps coming on like every 30 seconds. When it comes on, during idle, I can hear that the engine's revs go down about half normal idle for like a split second. Its like its having trouble supplying the fan with enough power to come on, let alone the damn fan wants to come on and go off all the time. After the fan comes on, the revs go back to normal. When I am driving it at any speed, I can feel hesitation, and the rpms go down a bit, when the fan comes on. But then the revs go back to normal. At night, when the headlights are on, they go dim at idle and also when I am driving it when the fan comes on. The way I know its the fan in both instances (driving and sitting at idle) is the fact that I do not have a filter on my radio and I can hear a whining noise at high and low pitches and its the same at idle as when I'm driving when the fan comes on. The fan makes that noise go to a higher pitch initially. (I know how to get rid of the noise, I just didnt do it yet)

Is it normal for the fan in GEN1s to want to go on and go off all the damn time? Its annoying. When I sit at a stop sign or red light, it sounds like a vacuum cleaner under my hood, its a bit embarassing too.

 

[CWhiteRun]

Check the output of your alternator to make sure it's charging the battery above 12V at idle. Sounds like your battery voltage is low and it could be due to the alternator not charging enough.

 

[eucharistos]

how is your coolant level?

 

[01sapphirebob]

Yes, check coolant. When was it last changed? Also, how old is the battery? Is it still the original? Could be a part of the problem as well. Alternator as mentioned above as well.

 

[viper067]

I would concur with the rest .... your battery is low, could be due to age or alternator not properly charging. A battery tender is a good thing to have. What temp is your engine at when the fan comes on? Sounds to me like you have the Roe fan kit installed and might not be properly set ... there would be a little black box behind the drivers headlight if it is installed

 

[Tom F&L GoR]

I have a '94 also and the OEM fan was a lightweight. I now have the later, central mounted fan and it takes more amps. If the voltage drops with the old fan, something is wrong.

I believe the PCM controls the idle speed with the IAC valve. If the fan comes on and the alternator supplies more power, but the idle speed drops, it could be that the IAC is not responding quickly enough because it is dirty or sticky. Since only air and blowby gasses pass through it (fuel does not, so it isn't kept clean with detergent gasolines) it only gets worse and worse.

More comments: The fan may come on because you have activated either the air conditioner or the defroster. Both engage the A/C compressor and the fan (at high speed), and I am fairly sure the fan comes on regardless of coolant temperature.

Further, on my '94 the voltage when the A/C compressor and fan is "on" is close to 15VDC. I had an old radar detector with built-in voltage gauge that would beep when the supply voltage got too high, which would happen with the A/C on.

It could be that the lights aren't dimming when the fan comes on, but rather dimming when the fan goes off and the PCM tells the alternator to only provide 13.5V instead of 15V.

Lastly, try driving with the A/C or defroster on. This should make the fan run at high speed all the time, and only at high speed. Then see if the lights dim, power changes, etc. If so, then something else is going on. Good luck.

 

[sgreiner1011]

Thanks Guys, I will check the above. Sorry I didnt get back to you earlier, I had the email notification on this thread and didnt get any notifications when you replied. I didnt think anybody replied. Thanks, I'll get back to you.

 

[sgreiner1011]

Ok, My coolant level is fine. My battery is at 12.8V when its not running. The alternator is charging at 14.2V when running. The fan is coming on every 17 seconds, and it stays on for 10 seconds. It just keeps doing that for as long as the car is running. When the fan comes on, the voltage drops to about 13.5V for a split second and then comes back up to 14.2V. I do not see a Roe fan system in the car anywhere. The fan comes on between the second and third tick mark at the very top of the temp gauge right above where "190" is labeled (there are 3 tick marks at the top, it comes on between the 2nd and 3rd tick marks) I didnt get to check the IAC yet, as I will have to take the sill out to get to it. Its packed in pretty well. I have the service manual and I am looking at the fan system now. Does anybody have any other ideas? Thanks, SG P.S. As I was under the hood, I found out that my power steering res cap is missing....WONDERFUL!

 

[sgreiner1011]

Basically Guys, I am wondering if your fans come on and go off as frequent as mine? (of course Roe fan system would be different) I mean whoever has a stock fan.

I looked at the schematic for the fan relays and it its not right. Both relays' coils are connected in the schematic. That doesn't make sense because the fan on relay would be energized at the same time the fan on (fast) contacts of the other relay would be on. This would mean the fan slow contacts would never be on. So much for the book.

 

[dave6666]

So much for the book? Or, so much for your understanding of the way the cooling system works. The coolant temp sending unit calls for the fan on via the PCM and therefore the fan on-off relay energizes. Assuming the coolant temp is below the threshold of needing the fan on high the hi-lo relay remains unenergized and the fan runs on low. If the coolant gets hot enough the PCM will energize the hi-lo relay and then the fan runs on high speed.

I would pull your relays and inspect the sockets. Replace both relays. They are generic $5 items. If no progress replace the sending unit and/or inspect the connection at the sending unit. Inspect the connection at the fan including the locations of the engine ground and the fan harness ground. You will likely need that book for those connections as the book calls them out. Lastly I would suspect the PCM.

When I redesigned my cooling system to 3 fans I built my own control scheme independent of the factory sensor/PCM/relays. I did that on my '01 not to fix anything but because I could. It could easily be done on an earlier Gen 1.

 

[sgreiner1011]

No, I mean so much for the book. I have already found 2 mistakes in it, so why not another? The coils of the relays are labeled in series with either other. Which means both coils would energize at the same time when the PCM calls for it. The normally closed contact portion (low fan) would go open when the fan on relay is closed, hence never letting the low fan speed operate. Also, whats really bad is that both relays are labeled in series with each other, plus one side of that circuit starts at pin 35 of the PCM, goes through both coils, then routes right back to the same pin 35. Can't have that. Should route to a different pin or somewhere else.

Does your viper's fan come on all the time like mine? I am not so worried about the electrical part right now, I just want to know if this is normal or not. I know its not normal for the lowering RPMs/dimming headlights to happen when the fan comes on. I just want to know if anybody else has the fan on/off issue.

I will be looking at the relays sometime soon. If worse come to worst, I'll probably do the same thing and make my own circuit. I make 6 figures working on 30 million dollar machines for a micro chip company and came across plenty of mistakes in schematics so far in my 10 year tenure.