vettewagon

Hey people. I have a 93 that keeps blowing cooling fan relays,(both). I jump the A to F on the relay plug jack and the fans run no problem. I put in new relays they work for about 5 to 10 minutes and botta-bing they are deemed useless. So can any one give me a little insight. It would be greatly appreciated.

gbrtng

So what happens to the relay - does the coil go open circuit?
Or other failure?

vettewagon

The coil goes open any clues?

Hooked on Vettes

If you're jumping pin A to F at the relay socket
with the relay installed, the 12 volts for the fan
is coming from a 5 amp fuse.

The current drawn by the fan motor is passing thru the
primary relay coil which is most likely causing the primary
relay coil to burn open because of the excessive current
flow before the 5 amp fuse can blow.

If you look at the schematic, if you want to bypass the fan
relay you would jump pin A to pin E at the relay socket.
That would provide 12 volts from either a 30 or 40 amp fuse
direct to the fan motor.

If you want to test both fans jump pin A to pin B on the
diagnostic connector above the drivers right knee and
turn the ignition ON. The computer will activate both
fan relays and both fans should run.




C

gbrtng

Those are 12 volt relays - designed to have 12 volts across the coil for an indefinite period of time. I'm guessing the coil draws about 1/2 to one ampere - I'll go measure the resistance of one later.

However, if the coils are burning out, they are getting hit with voltage much higher than 12 volts - and that does not exist in the relay control circuit. I'm stumped.

Can you relate any vehicle event when this started happening?

vettewagon

The car doesn't give any indication that it's happening, in fact the analog temp gauge reads around 180 but when I use the digital (orange) to read it shows actual jumping up and over 210 degrees. Then the car starts misfiring and running terrible. then I test the relays and they're both open.

gbrtng

Not true - the relay coil is fed by a 5 amp fuse, and the fan motor is fed by a 40 amp fuse.

It's interesting that my 91s have two fusible links instead of the 40 amp fuses feeding the fan motors.

vettewagon

I find it strange that a voltage spike would take out the relays and not a fuse

gbrtng

The ECM has a solid state switch (transistor) that grounds the relay coil circuit causing the relay to "operate" and the normally open relay contacts close to turn on the fan. Since both relays fail at the time the engine begins misfiring, I'm wondering if the ECM itself is failing in some weird way where it's hitting the coils with a high voltage transient.

Are you seeing a service engine light when this happens? And does the engine run normally after it cools back down?

vettewagon

Yes when the engine cools it runs good again. The service engine light never comes on.

Hooked on Vettes

In 93 GM started using Maxi fuses to replace most fusible links.

Read his first post. He jumped pin A to pin F.

All the current for the fan motor passed thru the primary
relay coil. High voltage didn't cause the relay coil to open.
Excessive current would.

vettewagon

Ok I jumped on the diag. connector above knee, A+B and both fans ran well. I inspected all related harnesses for the fan circuit and found nothing obvious wrong. So where does the lead me? I did finf that the voltages are all getting to the relays and they (relays) are definitelynot working.

Hooked on Vettes

That indicates there is nothing wrong with the fans, relays or the
ability of the ECM to control the fans.

If any fan relay was bad it was because you shorted pin A to pin F instead of pin A to pin E.

You said the temperature reading is jumping around when you look at
the digital gauge, that would indicate something could be wrong
with the Engine Coolant Temperature Sensor. It's screwed into the
lower part of the water pump. The connector has two wires going to
it. A Black wire which is ground and a yellow wire which is a 5 volt reference voltage.

Verify the sensor is not leaking and the connector is secure. The
ECM uses that sensor to determine the engine temperature. If it's
bad it could cause your problem.

gbrtng

If both fans run when A and B are connected, both fan relays are OK as well as the wiring and fans. So where are the two relays you claim are bad?

BTW, one or both fans should run when the AC is on also ...

jtc44

Both relays blowing up is strange how about a voltage spike from a bad alt. ? Hi draw from fans cousing heat in relay? We need to check voltage and current at the relays and fans thats all I got

pcolt94

After reading all the posts in this thread it just makes me want to start from square 1 at the beginning. I think the thread is going in the wrong direction because the initial information might not be correct. I also question if the relays are bad. These relays are a real rugged piece of hardware not a solid state device where a transient might take it out.

I’m sure you can put 50% more voltage to the coil with no damage and probably can put double the voltage to it. To burn up a coil with voltage, it would smell and might turn black as it burns up.

You cant put to much current thru the coil. One end has 12 to 14 volts on it and the other end of the coil is grounded. Current is a function of voltage with a fixed resistance (ohms law). The voltage would have to be about 24 volts for a period of time to double the current to kill it. I don't see that symptom.

I’m betting the measurement is being made wrong and the coil in the relay is good. And the actual symptom of the problem is not being accurately addressed. Were spending to much time on fan operation at this point.

I’m not sure I actually understand what the real problem is. It at least sounds like the engine runs bad when it gets hot. I’m not sure if the fans are on or not but 210* is not hot (its normal) and the fans are not on at that point anyway (providing A/C is not on).

To make a leap of an educated guess, it almost sounds like the ICM or opti is causing the engine to run bad. And when it cools down it runs good….sound familiar.

So am I possibly on the right track or should I go…..

vettewagon

Sounds good so far so your saying the car is in the norm. around 212?

pcolt94

I got to ask this first, how long have you owned the car and what have your temps been?

I believe the primary fan (left) comes on at 228* (or with the A/C), and the secondary fan (right side) comes on at 239*. Each fan will take the temp down about 10* before it cycles off. You may not like the temperature up at 240* but it is a normal for the car. Over 240 is getting into the overheating area and at 260 you shut the engine down.

When driving down the road at 50 or so a normal temperature should be 193-205 for this time of year. Stopped in traffic it will start to climb if no fans are running till the 228. Or you can turn on the A/C.

Are you familiar with this mode of fan operation?

vettewagon

Thanks for your help, maybe I'm on the right track now. First I have only owned the car for a month. I usually shut the car off by the time it hits 200, stands to reason when I jumped the A+B terminals on the diag. block the fans operated. I was testing the relay's when they were'nt energized...Duhh I'll run the car later and check till it does kick on the fans. Back to the car operating like crap when it heats up. Where can I go from here...? I should have stuck with my 84..lol

pcolt94

Its a newer car with a bit different technology but you will learn it. Do you know what the ICM and opti is in the spark and ignition system. These might be different items for you. If you want to support your car, get an FSM. Each year is specific and different.

As I said in my post the ICM (ignition control module) and opti (opti-spark distributor) are two items that can break down from heat and are commonly replaced. These items typically do not throw codes so replacement may be the only verification.

Search and read about these items on the Forum and internet to come up to speed.
Knowing a systems theory of operation will help you fix anything more efficient, faster and less costly.

Checking for fuel pressure and spark are still basic things to do as with any engine depending on problem.