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sampathapg

Corolla 1998 Radiator Fan Working Continuously

Question

Hi dear friends,

My Car is TOYOTA Corolla AE110 XE Saloon (1998, Auto, Petrol)

Recently I purchased this car from another person. Car is in mint condition.

But there is a problem.

The radiator fan working continuously. My knowledge about auto electrical is very poor.

But I checked the problem with my knowledge.

The fan is switching by an original relay. (Normally closed relay)

There is no voltage at relay coil, so the relay always closed. Then the fan is working nonstop.

I tried to find, the operation voltage of fan relay, but I couldn't find the it.

Then I thought the problem is with "Thermostat Sensor"

Then I went to an auto electrician, He said the thermostat wire has disconnected in somewhere. But he couldn't find it,

My questions are,

(1) what is the other end of thermostat sensor wire?

(2) How can I find it?

(3) How to check thermostat sensor is good or bad?

Please help me. Thanks.

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The issue is most of the time that either the thermostatic sensor has become disconnected, the fan relay is stuck, or the sensor itself is faulty.

It could have been intentionally bypassed by the guys who last worked on the AC as well.

I'm not familiar with the engine so not sure how exactly to figure out where these components are but the thermostatic sensor is usually on the hot water line (follow the pips into the radiator on top) or connected to the radiator itself.

Take the car to an auto electrician who will very quickly figure out the issue.

Edited by The Don

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Is your AC system working normally? Now that you have identified the relay see if the two wires connected to it are BLK/YEL and BLU/BLK. If the color coding is the same you should get battery voltage (measured with respect to chassis ground) on BLK/YEL as soon as you turn ignition on. If not the problem should be in that particular wire which runs to the fuse box under the dashboard to a 10A fuse. There are other things fed from this fuse and hence the fuse must be OK. If you have battery voltage on this see if the BLU/BLK wire runs to the AC pressure switch (4 terminal device located near AC condenser). First confirm these things before proceeding further.

Edited by Rumesh88

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What will happen if you pull out the relay.

Check whether there is a bridging wire on the socket of the relay, you will see this if you pull out the fan relay.

My suspicion is, someone had removed the wire from temp sensor so it won't send any signal to the relay and to make the fan working all the time either from the relay socket (easiest place to bridge and supply 12V live supply all time when ignition is switched on ) or elsewhere some bridging has been done.

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Is your AC system working normally? Now that you have identified the relay see if the two wires connected to it are BLK/YEL and BLU/BLK. If the color coding is the same you should get battery voltage (measured with respect to chassis ground) on BLK/YEL as soon as you turn ignition on. If not the problem should be in that particular wire which runs to the fuse box under the dashboard to a 10A fuse. There are other things fed from this fuse and hence the fuse must be OK. If you have battery voltage on this see if the BLU/BLK wire runs to the AC pressure switch (4 terminal device located near AC condenser). First confirm these things before proceeding further.

Rumesh, as i understood the issue is the fan works continously and that means the live supply towards the relay is there and it's given to the fan by bridging the relay mechanism.

The coil of the fan relay magnatizes when it gets live supply (ignition on) and ground supply (from the temp sensor). Since the wires from temp sensor were removed, there's no way relay can be activated though the live supply through the fuse box is available at the relay socket. correct me if i'm wrong.

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Rumesh, as i understood the issue is the fan works continously and that means the live supply towards the relay is there and it's given to the fan by bridging the relay mechanism.

The coil of the fan relay magnatizes when it gets live supply (ignition on) and ground supply (from the temp sensor). Since the wires from temp sensor were removed, there's no way relay can be activated though the live supply through the fuse box is available at the relay socket. correct me if i'm wrong.

No. The relay is a normally closed type thus acting as a fail safe mechanism. My analysis is based on that.

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No. The relay is a normally closed type thus acting as a fail safe mechanism. My analysis is based on that.

nomally closed and open by the temp signal is usually the mechanism i've seen in euro models but most of the japanese fan mechanism i've seen otherway around. Don't know exactly how it works in 110 though.

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Today I checked my Corolla AE110 Car again.

* It Comes with "Normally-Closed" Relay (4 Pin)

* The Positive (+) Line of the radiator fan is switching by this relay

* I checked there is +12V on both pins of the relay Coil (But no voltage difference in each pin, It's 0V, So the relay is not activating)

* Therefore the fan is working continuously

* The thermostat sensor comes with single wire

* I think the body of the thermostat sensor is working as other terminal

* Both terminals are reading as short-circuited with the chassy (Battery -)

* There is no direct connection with the fan relay.

* I couldn't find any modified point in this circuit

Please help me to solve this problem.

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Today I checked my Corolla AE110 Car again.

* It Comes with "Normally-Closed" Relay (4 Pin)

* The Positive (+) Line of the radiator fan is switching by this relay

* I checked there is +12V on both pins of the relay Coil (But no voltage difference in each pin, It's 0V, So the relay is not activating)

* Therefore the fan is working continuously

* The thermostat sensor comes with single wire

* I think the body of the thermostat sensor is working as other terminal

* Both terminals are reading as short-circuited with the chassy (Battery -)

* There is no direct connection with the fan relay.

* I couldn't find any modified point in this circuit

Please help me to solve this problem.

If you can identify which pin the thermostatic sensor wire connects to in the relay, check if there any breakages in the wire between the thermostat and the relay using a multimeter.

If the thermostatic sensor has only one wire that means it provides the earth of the connection. Check if the other pin of the circuit (not the one connected to the fan) has a positive connection as that completes the circuit.

Does the fan get its negative or positive connection via the relay? (usually negative but do check).

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Is the wire going to thermostat is of light green color? If so the other side of the wire should go to the AC pressure switch (search for it on the high pressure side of the AC before the expansion valve). If you find it, see if you have continuity between BLU/BLK and light green terminals. Also the 12V coming through the relay coil should appear on the BLU/BLK wire. Now remember all what I say could be wrong if the color code is something else.

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any possibility of finding a similar working temp sensor ? if so do this test.

  • remove the socket from existing temp sensor
  • fix it to the test temp sensor
  • give a (-) supply to the body of the test sensor.
  • if this activates the relay and stops the fan, your existing sensor is faulty.

if this test proves that there's nothing wrong with the existing sensor, you can proceed with finding the issues in the wiring loom.

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Is the wire going to thermostat is of light green color? If so the other side of the wire should go to the AC pressure switch (search for it on the high pressure side of the AC before the expansion valve). If you find it, see if you have continuity between BLU/BLK and light green terminals. Also the 12V coming through the relay coil should appear on the BLU/BLK wire. Now remember all what I say could be wrong if the color code is something else.

Dear Mr.Rumesh,

Yes it's light green wire,

How can I easily find the AC pressure switch?

Next step is not clear, please kindly explain me again.

(I checked the Radiator Fan relay socket when removed the relay, Both pins connected to the relay coil are reading as +12V, why is that?)

Thanks

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Dear Mr.Rumesh,

Yes it's light green wire,

How can I easily find the AC pressure switch?

Next step is not clear, please kindly explain me again.

(I checked the Radiator Fan relay socket when removed the relay, Both pins connected to the relay coil are reading as +12V, why is that?)

Thanks

That's normal because this relay is in parallel with the AC fan relay. If you unplug the AC fan relay you would get 12V only on one terminal. Next thing on this electrical line is the AC pressure switch. In some models it is located near the condenser and in others near the evaporator just before the expansion valve but always on the high pressure line. All you need to do is to physically follow the path of refrigerant line from compressor (through condenser, receiver/drier and expansion valve) to the evaporator. This is the high pressure line. The other line which runs from evaporator to the compressor directly is the low pressure one. AC pressure switch is a four or two terminal switch which is directly on the high pressure refrigerant line and is clearly visible if mounted near the condenser but a bit difficult to reach if located near the expansion valve for it the then under the dashboard. This switch must have one wire light green (coming from the temp sensor) and another BLU/BLK . Switch is normally closed.

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That's normal because this relay is in parallel with the AC fan relay. If you unplug the AC fan relay you would get 12V only on one terminal. Next thing on this electrical line is the AC pressure switch. In some models it is located near the condenser and in others near the evaporator just before the expansion valve but always on the high pressure line. All you need to do is to physically follow the path of refrigerant line from compressor (through condenser, receiver/drier and expansion valve) to the evaporator. This is the high pressure line. The other line which runs from evaporator to the compressor directly is the low pressure one. AC pressure switch is a four or two terminal switch which is directly on the high pressure refrigerant line and is clearly visible if mounted near the condenser but a bit difficult to reach if located near the expansion valve for it the then under the dashboard. This switch must have one wire light green (coming from the temp sensor) and another BLU/BLK . Switch is normally closed.

OK, I will find it.

Thanks in advance.

Edited by sampathapg

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A piece of advice - It is not a good idea post your contact details on a public forum. Better delete it and PM me.

Edited by Rumesh88

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A piece of advice - It is not a good idea post your contact details on a public forum. Better delete it and PM me.

OK, I sent you a PM.

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