What would cause my radiator fans not to run - 1994 Toyota Camry

not really a non running fan can cause overheating------ overheating problem --check fluid level--test coolant--check oil and coolant for mix problem ---water pump --etc

If an engine runs hot due to a partially blocked radiator the electric fan would be running most of the time.

If the fan doesn't run at all it suggests it isn't working and while that alone is likely to cause overheating in many driving scenarios, it is worth noting a car with a well designed cooling system in good order should rarely need the benefit of an electric fan when cruising at light load mid speeds.

It is possible the car has reached an age where it would be worth giving the cooling system a birthday along with repairing the cooling fan - replacing the thermostat and flushing the system thoroughly, including ensuring the radiator core is clear and nothing inhibits the air flow...

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The engine computer grounds the relay to make the fan run. Will the fan run if you bypass the computer and ground the relay ?

There are certain positions for the climate control system that will cause the A/C system to activate. When the A/C is on, the radiator fans automatically run to provide airflow thru the condenser coils in front of the radiator. This could be the issue. Turn off the climate controls and recheck.

Usually a bad water pump will cause the engine to run hot with or without the ac being involved. The most common cause of overheating with the ac on is not enough air flow thru the radiator.

Many engine control system faults can cause the radiator cooling fan to come on and run non-stop. Also, if your A/C is on or if you have your heating and cooling controls in DEFROST mode, this can cause the radiator cooling fan to come on (normal operation). Or there could be a cooling fan circuit malfunction (like a stuck relay) causing this to happen.

Check to see what mode your climate controls are in. If the climate controls are not in A/C or DEFROST modes, then you should have your engine control system properly diagnosed to determine the cause of the radiator fan being on continuously.

Also, if the Check Engine light is on, this is a clue that the engine control system is malfunctioning.

CHECK TO SEE IF BOTH COOLING FANS RUNNING ARE RUNNING WHEN ENGINE RUNNING START OVERHEATING IF COOLING FANS NOT WORKING CHECK COOLING FANS LARGE FUSES IN THE ENGINE COMPARTMENT OR YOU COULD FAULTY COOLING FANS THERMO SWITCH BOTTOM LEFT SIDE OR RADIATOR.IF COOLING FANS IS WORKING WHILE ENGINE RUNNING.RADIATOR CORES AND HEATER CORE COULD BE CLOGGED.COOLANT SYSTEM NEED FLUSHING. THE THERMOSTAT PARTIALLY CLOSED CAUSE ENGINE OVER HEAT.CHECK WATERPUMP WEEP HOLE IF LEAKING WATER PUMP NEED REPLACING.

Yes, cause that sensor operates the electric cooling fans by the radiator, if those fans or fan don't come on, the radiator can't cool down as quick and causes the engine to run hotter.

You may have air trapped in the cooling system, this causes a hot spot and the fans run, This is a common issue on most front wheel cars, jack the front of the car up as high as you can, fill the coolant reservoir full, run the engine until hot,( don't overheat it) then shut down, let the engine cool, this should self bleed the air, refill the coolant bottle and retest for your problem, restore the wiring, the not running fan is for AC. Spray cold water from a hose on the radiator his will help get the air out after the shut down.