Electric Fan

My electric fan on my '97 comes on for few seconds and goes off just as quick. No clue why, anyone had a similar issue. I would guess it is the thermostat sensor on the fan but??? Any ideas?

97 the fan is controlled by the PCM, and the PCM decides that based on inputs from the CTS in the thermostat housing.

I would start by testing the CTS.

On the 97 the A/C system cycles the fan on/off as long the A/C is engaged. Defrost also engages the A/C. Low r-134a refrigerant will also cause rapid cycling of the A/C compressor. Check the R-134a level.

Where are your climate controls set to ?

Before you start checking pressures, put the HVAC controls to vent and see if it stops cycling. 97 and up cycle on defrost both to aid demisting and to keep the refrigerant seals in shape.

Tim_MN said:

On the 97 the A/C system cycles the fan on/off as long the A/C is engaged. Defrost also engages the A/C. Low r-134a refrigerant will also cause rapid cycling of the A/C compressor. Check the R-134a level.

Where are your climate controls set to ?

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I stand corrected. Do you remember the year the aux fan operation was turned over to the PCM only?

My 97 A/C cycled the fan on/off. My 99 does not. 96-97's will blink OBD-II codes on the dash, most 98 and all 99-01's do not. I would suppose that early 98 was the transition year for both behaviors.

Tim_MN said:

My 97 A/C cycled the fan on/off. My 99 does not. 96-97's will blink OBD-II codes on the dash, most 98 and all 99-01's do not. I would suppose that early 98 was the transition year for both behaviors.

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Thanks Tim.

joe_peters said:

I stand corrected. Do you remember the year the aux fan operation was turned over to the PCM only?

Click to expand...

91 when it went to the Chrysler computer. From there up the A/C clutch and CTS feed into the computer, which has dominion over the fan

Prior to that the fan was controlled by temperature switch

Thanks guys, all of the answers will help I guess I should have been more specific with what fan it is. This is the electric cooling fan on the radiator. I have a new fail safe thermostat to goon it, so I will try that first. Also going to look into the coolant temp sensor.

All great advice though and now some ideas to chew on in the morning. I will let you all know what I find.

Thanks again

That is the fan they're talking about. Assuming you don't have the AC or defroster on, some details would aid diagnosis. Is the Jeep running hot?

No clue as to engine temp. No temp gauge installed yet, bought an auto meter gauge set so I will get to see. The fan starts to cycle on and off once the engine comes up to temp. Then the fan turns on for a few seconds then back off, then back on a few seconds later. Makes me think the fan is over amping and shutting down or whatever controls it is on the fritz. I have Haynes out but it's not saying much. Next is to start looking through the prints and digging through that part of the electrical system.

You just have the "dummy light" gauges?

The haynes manual isn't good for much on the 97+. The Factory Service Manual is the way to go if you can grab one.

Quick and dirty test for the fan would be to jumper it to the battery directly. If it runs well and normally, you can move on to troubleshooting the CTS, relay, and I'd recommend checking the mechanical fan clutch and going over the cooling system in general.

This is out of a 2000 FSM, YMMV

Electric cooling fan 4.0L: With or without A/C
request the electric fan will come on only when the
coolant temperature is at least 106° C (223° F), and
will remain on until the coolant temperature drops to
103° C (217° F) or below. Regardless of coolant temperature,
When air conditioning system pressures
reach 2068.5 6 138 kPa (300 6 20 psi) the electric
fan will engage and continue to run until the A/C
system pressure drops to 1620.3 kPa (235 psi) minimum,
then the electric fan will shut off.

ELECTRIC COOLING FAN AND RELAY DIAGNOSIS
NOTE: Refer to Electrical Group 8W for electric
cooling fan and relay circuit schematic.
The powertrain control module (PCM) will enter a
diagnostic trouble code (DTC) in memory if it detects
a problem in the auxiliary cooling fan relay or circuit.
Refer to Group 25, Emission Control Systems for correct
DTC retrieval procedures.
If the electric cooling fan is inoperative, check the
15A fuse in the junction block and the 40A fuse in
the Power Distribution Center (PDC) with a 12 volt
test lamp or DVOM. Refer to the inside of the PDC
cover for the exact location of the fuse. If fuses are
o.k., refer to Group 8W for electric cooling fan and
relay circuit schematic.