1996 Honda Odyessey engine cooling fans don't come on and engine on and engine temperature tends to go up. it will only come on when the AC is switched on. i do not need to run the AC all the time but i have to to keep the engine temperature down. please help to resolve this problem.

Do you mean when your AC is on if so your cooling fan May not be working

Sounds like your radiator cooling fans are not working.

there are up to 4 fans, in cars. varies by years, and options.
heater /cooling fan in dash. (cab fan)
front leading edge A/C condenser fan
and up to 2 engine RAD fans.

are all dead?
does car have working A/C?

cooling for engine or occupants?

if you got to alldata.com the drawing is there, and how the logic works.
cars with low hoods, tend to have 2 RAD fans, (long skinny rad)
im too lazy to look it up ,until you state exact fan.

if engine at long stand still,the engine temperature will rise about 190 degrees the cooling fan suppose to automaticaly turn on when coolant temperature sensor get hot it cause its resistance decrease causing pcm to send power to coolant fan relays and cooling fans, when you turn on AC the cooling fans suppose to turn on to cool down AC CONDENSOR, IF NOT AC WONT WORK COOLING FAN COOLS DOWN REFRIGERANT SO IT CAN RECYCLE THROUGH THE SYSTEM AGAIN.your cooling is suppose to turn on when engine at a sit still if vechicle not moving as coolant temperature rises at a set point the cooling fans will turn on cool down engine.cooling fans dont turn on when you first cold stsrt vechicle unless you have AC SWITCH ON.if cooling fans dont turn on when vechicle at a long stand still or moving along slow traffic.if coolant temperature sensor been replaced and fuses and relays okay have dealership check see if pcm driver circuit working faulty pcm will cause cooling fans not to turn on.

Probably the temperature sending unit...if not that the relays...they should be relatively cheap and easy to replace...

YOUR AIR CONDITIONER PUT LOAD ON ENGINE CHECK TO MAKE SURE RADIATOR COOLING FAN RUNNING BECAUSE IT HELPS TO KEEP THE ENGINE COOL AND AC CONDENSOR COOL FAN NEED TO BE RUNNING IF NOT CHECK COOLING FAN FUSE OR RELAY.

You will probably need to replace the resistor behind the dash. Usually the first symptom is the fan will only blow on high but not on the lower speeds. If that is the case, then the resistor ( cheap fix) is the culprit.

If you just lost it all of a sudden, you should check for a bad fuse and will probably find other things that don't work too. Replace the fuse and watch to see that it doesn't go out again - which if it does, you have a short somewhere that needs to be fixed.

The older Dodge neon cooling system has always been a problem, so this will not be easy to diagnose and repair.

A little background. There is a temperature sensor in the coolant system that sends that information to the PCM and the PCM then sends a signal to your temperature gauge to register it. Once the temperature of the preset peak, the PCM then sends a signal to the cooling fans to turn on, so the do NOT run at all times when the engine is turning, only when the coolant level reaches a preset level (in the 200F to 235F range). The one exception to that is when the AC is turned on, the radiator fans should be told to turn on. So start the car, turn on your ac and see if the cooling fans turn on. If yes, you don't have a problem with the cooling fans. But that doesn't mean that you don't have a problem with your cooling system. If the car is overheating, you need to find out if the PCM is sending a signal to the cooling fans to turn on. If it isn't the trouble could be in the PCM.

The cooling fan is supposed to come on when the /ac compressor clutch cycles on, and off when it cycles off.
The idle speed kicks up to compensate for the additional a/c compressor load and the additional alternator load. usually, just the low speed comes on until it hits a much higher temperature.

the system should cycle 4 to 7 times/minute at 79 degrees F.

Here are some things to consider:(The PCM (engine computer) is NEVER defective, don't replace it). I don't think it is the ECT (engine coolant temp sensor) or the Cylinder Head Temp Sensor. Or the VSS or the MAF sensors.


The electronically controlled fan clutch is controlled by the powertrain control module (PCM) based upon requests for airflow to cool the engine, transmission and A/C condenser. If no cooling is required, the electronics permit the fan to spin at a slower speed yielding improved fuel economy.
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Inoperative or damaged:

• Electronically actuated fan clutch
• Electronically actuated fan clutch controller
• Wiring, connectors, relays or modules
• Engine Coolant Temperature (ECT) sensor (4.0L SOHC)
• Cylinder Head Temperature (CHT) sensor (4.6L [3V])
• Mass Air Flow (MAF) sensor
• Vehicle Speed Sensor (VSS)
• ----------------------------------------------------------------------------

If the cause is not visually evident, connect the scan tool to the Data Link Connector (DLC).
Retrieve any DTC Codes (Diagnostic Test Code). Autozone will do for free.

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The cooling fan clutch actuator valve controls the fluid flow from the reservoir into the working chamber. Once viscous fluid is in the working chamber, shearing of the fluid results in fan rotation.

The cooling fan clutch actuator valve is activated with a pulse width modulated (PWM) output signal from the powertrain control module (PCM). By opening and closing the fluid port valve, the PCM can control the cooling fan clutch speed. The cooling fan clutch speed is measured by a Hall-effect sensor and is monitored by the PCM during closed loop operation.

The PCM optimizes fan speed based on engine coolant temperature (ECT), engine oil temperature (EOT), transmission fluid temperature (TFT), intake air temperature (IAT), or air conditioning requirements. When an increased demand for fan speed is requested for vehicle cooling, the PCM monitors the fan speed through the Hall-effect sensor. If a fan speed increase is required, the PCM outputs the PWM signal to the fluid port, providing the required fan speed increase.

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automatically. even if the motor is off.