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Discussion Starter · #1 ·
So the other day my cooler fan relay blew. I had to temporarily short the connector with a cotter pin and duct tape to get the car home without it overheating. This melted most of the connector. So today I replaced the connector and the cooling fan relay and the fan still wont turn on over 221 degrees.

-Maybe one of the two temperature readers that tells the fan to go on is bad?
Any help is greatly appreciated, I'm trying to have her on the road by Friday for Carlisle.
Thanks
 

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How did you know that the relay was bad?

Why did the connector melt? Shorting across the connections on the connector shouldn't have been electrically different than the relay (unless the cotter pin offered really high resistance, but it doesn't seem likely just off the top of my head).

Have you verified that the new relay and connector replacement is actually providing current to the fan at temperature?

Is there anything else that makes you think that the sensor would have failed at about the same time as the fan relay?

Steven
 

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Discussion Starter · #3 ·
How did you know that the relay was bad?

Why did the connector melt? Shorting across the connections on the connector shouldn't have been electrically different than the relay (unless the cotter pin offered really high resistance, but it doesn't seem likely just off the top of my head).
I believe the cotter pin must have been offering a higher resistance than that of the original switch because it got so hot that as soon as it touched the plastic connector it started to melt it, within a second or two. Just to clarify, only the plastic part of the connector melted until it was flush with the four metal prongs that actually conduct the current for the switch.

Have you verified that the new relay and connector replacement is actually providing current to the fan at temperature?
Actually I only tested that the relay was in working order by swapping it with another 84 vette. I did not check the connector because I just assumed that it was in fact providing a current before I replaced it so why would it not provide a current now? But you know what happens when you assume, I'll make sure to test it tomorrow asap.

Is there anything else that makes you think that the sensor would have failed at about the same time as the fan relay?
It's just the first thing that came to my head, but it is extremely unlikely for both to spontaneously stop working.

Thanks,
Yosi
 

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It sounds like you shorted the wrong two connections to make your fan come on. Nothing should have melted just because you jumped the two connections.
Get/buy/borrow an electrical service manual for your car if you can and double check your color codes/connections to the relay.
Check all the fuses and wiring to the fan and relay.
 

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Not a mechanic here, but ...

My Corvette mechanic was displeased with how hot my 96 was running. Solution...New Radiator Cap (old was not holding enough pressure), New lower temp thermostat, Hypertech program install.

Running like a dream now...fast and COOL!!
 

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Replace the senser in the passenger side head. With a car that old I bet its bad. this is the main fan swicth.
 

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Same thing happened to my brothers 1987 vette. Found out a rock had gotten into the fan and wedged into the shroud and the fan was stuck. Have you tried to rotate the fan blades by hand?
 

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Discussion Starter · #8 ·
Here's the latest:
The fuse apparently blew and I overlooked it, BUT now the fan stays on, even when the car is off and not hot at all. I checked and double checked the wiring and it all looks good. I think you guys are right about the sensor, it must be broken since it doesn't know when to turn the fan off. Ill look into that tomorrow
Thanks everyone
:thumbsup:
 

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Replace the senser in the passenger side head. With a car that old I bet its bad. this is the main fan swicth.
No, bad information. That "sensor" in the passenger side head is actually the aux fan switch (if equipped as an option). It is nothing more than a resistance switch. When the coolant is hot the resistance is low and vice versa. It will not ground the aux fan until the coolant temp gets 238*.

The CTS (coolant temp sensor) located in the front of the intake manifold. That sensor that sends resistance to the ECM. When the engine temp gets 227*, the ECM will ground the relay and send voltage to the fan. This is unless some aftermarket fan switch or sort has be installed previously by someone.

To correctly bypass the fan relay temporarily, the first pin and last pin on the connector should be jumped with a fused jumper wire. Apparently the wiring at the fan relay connector is buggered up or the wiring at the ECM. :thud:
 

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just a side note, when my cooling fan died on my 84, I went and got a replacment motor for it. when I replaced it I took the old fan motor apart and saw how tore up it was inside. ( probably origonal to the car ) I know that it was operating way to inefecently for along time before that based on what I saw. it probably put quite a strain on the system feeding it electricity.

the new fan works awesome and keeps me about 5 deg cooler on average.

so as a side thought, a replacment motor for the fan is not that bad of an idea either, even if its not the problem , it will eliminate it as a potential problem in the system. :thumbsup:
 

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No, bad information. That "sensor" in the passenger side head is actually the aux fan switch (if equipped as an option). It is nothing more than a resistance switch. When the coolant is hot the resistance is low and vice versa. It will not ground the aux fan until the coolant temp gets 238*.

The CTS (coolant temp sensor) located in the front of the intake manifold. That sensor that sends resistance to the ECM. When the engine temp gets 227*, the ECM will ground the relay and send voltage to the fan. This is unless some aftermarket fan switch or sort has be installed previously by someone.

To correctly bypass the fan relay temporarily, the first pin and last pin on the connector should be jumped with a fused jumper wire. Apparently the wiring at the fan relay connector is buggered up or the wiring at the ECM. :thud:
Just to let you know the temp sensor in the passenger side head on my car works with the ECM to turn the primary fan on. The sensor in the drivers side head turns the secondary fan on at 235 degrees. I think the newer C-4 might be different. I know that the LT-1 flows differently.:thumbsup:
 

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hoopty, I'm sorry, but you are incorrect as well. I assume you have an 88 like is says in your profile. The "sensor" in the passenger side head (between #6 and #8 spark plugs....is the coolant temp sending unit for the dash gauge. It doesn't send anything to the ECM. The CTS in the front of the intake manifold is the sensor the ECM sees to determine fuel load at start up, idle speed, fan on/off time, ect. As long as the prom in the ECM is stock the fan(s) will come at the temps above.

I'm not starting problems, just give correct info.
 

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The CTS (coolant temp sensor) is located in the front of the intake manifold on the 84-91 C4's. It has two wires (yellow and black). The yellow wire might have a black stripe, it's been awhile since I looked.

84-85: The aux fan (if equpped) switch is located in the passenger side head between #6 and #8 spark plugs. It has a single green wire. If the aux fan is not equipped, the hole where the switch is will be plugged.

84-85: The coolant temp sender for the dash gauge or (IP) is located in the driver side head.between #1 and #3 spark plugs. It sends resistance signals to the dash gauge where the digital coolant display is.

86-89: The aux fan (if equipped) switch is located in the driver side head between #1 and !3 spark plugs. Single green wire.

86-91: The coolant temp sender for the dash gauge or (IP) is located in the passender side head between #6 and #8 spark plugs. It sends resistance signals to the dash gauge where the digital coolant display is.

90-91: Do not have a aux fan. They have two fans side by side..same as the 92-96. Both are controlled by the (90-92 ECM) or (94-96 PCM).

92-96: The CTS for the ECM or PCM is located in the water pump housing. This sensor sends signal to the ECM and the digital readout on the dash gauge.

Someone can correct me if wrong, but I believe the coolant temp sending unit for the analog guage is located in the driverside head between #5 and #7 spark plugs.
 

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Sorry my bad. My brother bought a cool fan switch for his 1987 vette last spring. I installed it in the passenger side cylinder head.When the car was warming up the temp on the gauge jumped from low to 240 degrees. the cooling fan never did come on I removed it and called hypertech. They said that the sensor in the passenger head sent information to the ECM and the cool fan switch could only be used to turn the secondary fan on. So I wired both fans to work together. I was relying on thier information I am glad to find out that was incorrect now I know where the correct sensor is located THANKS!:thumbsup:
 

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Discussion Starter · #15 ·
Problem is FIXED!!
Sorry for the delay, fixed it late Thursday and was in Carlisle all day yesterday.

So after tracking wires all over the car and testing for shorts and making sure the switch had a ground and a whole bunch of other stuff it turned out that the NEW relay was the wrong one. After taking it apart you could see that it was wired backwards. The relay switch was always open, and this means that when the fan would reach temperature where it should turn on, it would actually turn it off:bang . So I went back to the guy that sold it to me and he apologized and gave me a new working one this time. Such an easy fix and it drove me crazy for I dont know how long:laughing: Oh well.

Thanks for all of the great replies everyone!
RRT Vette great info, very informative reading, thanks bro:thumbsup:
 

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Discussion Starter · #16 ·
Someone can correct me if wrong, but I believe the coolant temp sending unit for the analog guage is located in the driverside head between #5 and #7 spark plugs.
Yes, I believe it is a blue wire as well
 

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My Fans Don"t Work Either>>>at All>

where is cooler fan relay located?
How do I start testing things? at the fan? and work back to relay? then CTS?

I have an 88 with both fans. ONe in front, one in rear of radiator.

only have a test probe...do I need a VOM?
 

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The relay for the secondary fan "the one in front of your radiator" is located on the fan shroud of the primary fan "the fan on the back side of your radiator". You can test the secondary fan circuit by unplugging the green wire located between number 1 and number 3 spark plugs on the drivers side of the engine. After it is unplugged ground it while the ignition switch is on and the secondary fan should run. I believe the primary fan relay is located on the inner fender drivers side close to the front reservoir of the master cylinder. Both relays have a large red wire that wire should have voltage if they don't you could have a bad fusible link. I assumed that you have already checked your fusees and none are blown. The primary fan is controlled by the ECM it should come on at 228 degrees and the secondary fan is controlled by the temp switch located between number 1 and number 3 spark plugs and comes on at 235 degrees.:thumbsup:
 

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thanks hoopty. I have searched in here and tried to find everything about narrowing the problem down.

I will try the test you suggested immediately.

Do you know if the primary fan relay is in front of the battery or one of the two behind it on the firewall?

Is there a way to jump the primary relay? which wires would I connect?

I bought a digital tester, but didn't see how it would help me. Total rookie with electrical.

Also the digital AC climate control is wacked....the digits just scroll through random blinking and stuff. The defrost button on it does work however.
Could this keep the fans from kicking on?
 
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