Cooling fan issue

[ChristopherB]

Hey guys so my cooling fan won't come on when the car heats up, it's a 89 Mazda 121. The fan comes on if I turn the AC on, replaced the sensor in the thermostat housing and the connector, still won't work, any ideas cuz I'm outta them?

[WmWatt]

Does the fan come on when directly fed current from the battery?

[1990new]

Assuming the 121 works the same as the Festiva, here is how it works:

1. The Cooling Fan Temperature switch is normally closed...
This mean that when the switch is turned to the on position and the METER fuse is not blown, power is going to the spring loaded cooling fan relay coil to hold it open. This prevents power from being supplied to the cooling fan circuit, so the fan does not run. When the coolant temperature reaches 207F or higher, the ground connection is broken between the temp switch and the engine head which stops the power to the relay which is holding the cooling fan circuit open and the fan will come on. This is the reason that your fan normally comes on when you remove the wire from the temperature switch... so if your fan is running when the switch is on, the coolant temperature is below 207F and the AC is not on, either you meter fuse is blown or your temp switch wire is off or your temp switch is bad.
2. If the car is equipped with air conditioning, an Air Conditioning Relay is in the circuit. Whenever the Air Conditioning is turned on, the Cooling Fan Relay and the Cooling Fan Temperature Switch are bypassed and the Cooling Fan Motor runs continuously when the switch is on.
(Since your fan runs when the AC is turned on this mean that your 20A cooling fan fuse is not blown)

First thing to do is (with the switch turned on) disconnect the wire to the temperature switch, If the fan does not come on, it could mean that the wire that goes to the temperature switch is bare somewhere and is touching metal and getting a ground somewhere else or your new temperature switch is also bad and not breaking the ground when the temperature reaches 207F. Another way to check is to remove you meter switch with the switch on.. if your cooling fan comes on when you do this, it is a pretty sure bet that you have a faulty temp switch or there is a short in the ground wire going to the temperature switch.

Never had one.. but irrc some of the 88 89 Festivas had a temperature sensor on the bottom left side of the radiator also... If yours has one of these, I am not familiar with how that comes into play with controlling the cooling fan. But according to my 1989 Electrical and Troubleshooting manual, that temperature sensor which has two connectors, (sot it acts as an on/off switch) sends a signal to the ECA when the temperature reaches 62.6 degrees F (17C). However it does not say what the ECA does with that information for an EFI engine. Also I'm not sure it the circuit completion is when it's below or above this temperature. Anyone know?

[WmWatt]

What 1990new wrote. From the Haynes manual "To test for normal fan operation disconnect the thermoswitch and turn the ignition key to ON. If the fan does not come on check the system components." The thermoswitch is on the thermostat housing.

[1990new]

I neglected to mention one other possibility.. Relays normally fail in the stuck open position which is why the cooling fan circuit was designed to allow the fan to run in a normal cooling fan relay failure situation. Although it is rare, it is also possible for the relay to fail in the closed position. If the spring should break in that relay, it could be the reason your cooling fan could not be triggered to come on by a good temp switch. If you have access to another cooling fan relay you could replace yours to see if that fixed the problem. The cooling fan relay is attached to the engine compartment wall on the left side. It is the first one of two (three on Canadian models with daytime running lights) that is closest to the wheel well, The next one up from that is the headlight relay, then the running light relay is the one closest to the headlight if there is one.

Again, since yours is a 121, I can't be sure the relays are in the same position as the Festiva.

[harpon]

Does it have both a temp sensor for the gauge and a temp switch, as an 89 would? Switches are easy- later year cars send a sensor reading to the ECM computer and that drives the fan- my 96 Aspire is doing this same thing- the mechanic fvcked it up when he put in a water pump and timing belt- I had tested it a day or two before and it was working then, but the car was overheating cause it needed the water pump. I haven't fixed it in two years because it comes on with a/c and I'm in Florida with that on most of the year.

Anyway back to the SWITCH- if it has a temp switch with a wide 3/8 NPT thread- simply establish another relay circuit- and you can get a LOWER temp fan switch on ebay- a 175 or 185 degree FAN ON switch is under 5 dollars- drain coolant thread in new switch-

https://www.ebay.com/itm/Universal-1...kAAOSwEWZdTUGK

they also have these great new battery terminals with line openings on them-

https://www.ebay.com/itm/Car-Boat-Ba....c100752.m1982

Just put one on the '91 Festy


run battery power through a cheap 40 amp relay to the fan itself- put an inline fuse on- they even have PAL inline fuses now-
run the control circuit from an ignition ON point and the other line to the top of the switch- the switch closes ground to turn open the power circuit to the fan when the key is ON and the temp rises to the switch temp. It runs the fan until it goes under again.

Total cost about $20, leave the original circuit in place - you'll have to splice in at the fan- so the a/c still turns on the fan too.

If your car has no temp SWITCH but only a sensor to ECU computer- you can still by-pass the OEM set -up with one of these switces installed in a COUPLING installed in the upper radiator hose- and that switch will fit into it with the bottom portion threaded- you have to do that with a Die from China, (And I guess you could DIE from Corona virus) I'm intending to install this one on the Aspire-

switch.jpg

Here's a thread on it I did a few years ago-
https://fordfestiva.com/forums/forum...ing-to-die-for

JULY2004 004.jpg
The Old '88- "Diana" aka The Coke Can

[ChristopherB]

You guys are awesome thanks for all the help and support! I'll let yous know how it goes