'91 Toyota Corolla 1.6, Radiator Fan always on with key on

JackC

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My friend's '91 Corolla's large left hand fan always runs with key on. The right hand smaller fan is off.

I have removed the fan relay at left inner fender and that stops the fan, of course.

Now I want to determine if it is a bad relay or a bad coolant fan switch. (I don't have another relay like that on to swap out, and didn't see one on the car to swap)

The fan switch is supposedly in the radiator, according to the parts info. (I don't have the car here now)

Is that radiator mounted fan switch normally open and grounded when hot or something else?

For those that work on Toyotas--which would be the most suspect, fan switch or relay?

BTW, the car does not overheat and the temp gauge works normally.
JackC
 

al daniels

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hey jack,its likely the fan switch or somebody jumpered the plug so the fan runs when the key is on.just test the two terminals for continuity.should be none when cold.
 

Jim Fairbanks

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Here you go Jack....hope this helps....Jim..............If coolant temperature is low (below 181°F), proceed as follows:
Turn ignition switch on and check that cooling fan does not operate. If fan runs, check for faulty fan relay and/or temperature switch. Check too for separated electrical connectors or severed wire between relay and temperature switch.
Disconnect temperature switch wire, then check that fan rotates. If fan does not run, check fan relay, fan motor, ignition relay and temperature switch.
Connect temperature switch wire.
If coolant temperature is high (above 199°F), proceed as follows:
Raise engine temperature to at least 200°F, then confirm that fan rotates.
If fan does not rotate, replace temperature switch
Using an ohmmeter, check that there is no continuity when the coolant temperature is above 93°C (199°F).
Check that there is continuity when the coolant temperature is below 83°C (181°F).

If continuity is not as specified, replace the switch.
INSPECT ENGINE MAIN RELAY Refer toComputers and Control Systems.
INSPECT COOLING FAN RELAY
Location: The relay is located in the engine compartment relay box.


Inspect Relay Continuity
Using an ohmmeter, check that there is continuity between terminals 1 and 2.
(b) Check that there is continuity between terminals 3 and 4.


It continuity is not as specified, replace the relay.
Inspect Relay Operation
Apply battery voltage across terminals 1 and 2.
(b) Check that there is no continuity between terminals 3 and 4.


If operation is not as described, replace the relay.
 

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Mobile Dan

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Dan's short version...

Key on, cold engine, fan running. Disconnect wires at switch. If fan stops, you have a bad switch. If fan continues to run, install jumper between switch wires. If fan stops, you have a bad switch. If fan never stops, look elsewhere, switch is OK.
 

JackC

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Al and Jim and Dan: Thanks. Exactly what I needed. Those relays are different than the GM style relays that I am more familiar with. I also was not sure about the operation of the radiator switch.
 

Mobile Dan

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I want to change my reply. Alldata is showing a different switch than what I was thinking. Apparently switch has a single wire and completes circuit to ground through mounting threads when internal contacts are closed. Looks like switch is mounted in "thermostat housing".

So. Key on, cold engine, fan running. Disconnect wire at switch. Wire color is labeled "LG" which I believe is "light green". If fan stops, you have a bad switch. If fan continues to run, ground switch wire. If fan stops, you have a bad switch. If fan never stops, look elsewhere, switch is OK. Or you have multiple problems.

Schematic also shows AC high pressure switch in same circuit, wired in series. Could be a factor. Looks like if either of these switches are open, relay #1 is not energized. Also possible that relay#2 provides power to fan through a different circuit with AC on. Way more complicated if vehicle has AC.
 

billr

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Danica, I loved your first version, so elegantly simple! Too bad the AC complicates things by also controlling that fan relay.
 

JackC

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Pulled radiator switch connection and fan still ran. Checked continuity of relay with help of Jim's diagrams and it was bad. Ordered one from RockAuto for $7.41 including shipping. Great price , as they ranged from $18-$ 25 at the local auto stores.

Thanks to ALL of you.

Fixed, I assume. Will see when part arrives. Didn't have a spare to check with.

JackC
 

NickD

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Circuit diagram and explanation is showing a normally closed contact that opens when energized. Seems backwards from any fan relay I have seen. Technical term is a form B contact.

Would be interesting to see the rest of the circuit. Since I have been playing with and designing relay circuits for some odd 53 years now. Pop open the cover and check the contacts, even have a relay contact burnishing tool and even some spare contacts I have been riveting in. If the solenoid is opened and the relay won't energized, typically, these only draw about 100ma. Then its time to consider a replacement.

Say consider, because I have ran across aviation type relays that are so rare, or extremely expense, was well worth the effort to rewind the coil. But certainly not for eight bucks.


Toyotas were noted for using a radiator sensor for fan control, was a good idea, because would typically click on at 160*F so the coolant temperature remained at 195*F. Not this thermal cycling in many domestic cars, constantly between 195-235*F. Been known to modify that as well. Engine and all that plastic lasts a lot longer.
 

NickD

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Looks like the guy that designed this wanted to do everything backwards. Closed contacts of relay 1 will keep fan 1 running. If silver contacts are used, at times these contacts will slightly weld together and can be snapped apart with a finger nail then the contacts burnished.

To stop the fan, both AC high pressure and water temperature switch have to be closed, so assume the AC switch is out of proper refrigerant pressure in the 40 to 410 psi range where fan operation is not required, or the radiator coolant temperature is below 160*F. If either switch opens, fan should not run as the solenoid of K1 is deenergized and the fan will run.

Solenoid of K2 is in parallel with K1 and will also be energized with either the AC or water switches closed. This appears to put the condenser fan in series with fan number one if the radiator temperature is low and the AC is kicked on. Kind of like half speed operation. If the radiator gets hot, fan one runs at full speed due to the closed contacts of K1, as the condenser fan, as K2 will also deenergized putting a full 12 volts acrossed it.

Circuit does make some sense, kind of, maybe, would be helpful if they add small comments, like opens at 160*F.
 

JackC

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WOW, if the new relay doesn't work (even though it checks out bad) I may have to do some more thinking with all this A/C stuff involved.

This old Corolla hasn't had a working A/C for years and the owner is never going to fix it. So, I may have to bypass , modify or whatever some parts.

And I also told him he could just drive it forever (which may not be too much longer-it is a real better) with the fan running all the time. The thermostat will keep it warm enough. It is only used about 50 miles a month, if that.
 

NickD

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Not too bad now that you know K1 has to be energized to stop the fan, this part as to be good and show a short circuit when cool:



Radiator temperature sender, seven bucks at rockauto.

If the AC isn't working, that pressure switch could have an open circuit, that you can short circuit. High side of the relay coil has to show 12V with the ignition switch on. That's it.
 

JackC

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My friend received the new relay today, installed it and all is well.
Fixed.

Now I will get the old one from him and take it apart and see if I can do a "NickD" fix just for fun.

Thanks to all. This continues to be one of the most professional auto repair sites on the WWW.
 
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