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Lights dim when e-fan kicks on..?

Y

yossarian19

NAXJA Forum User
Location
Grass Valley, CA
Just noticed it last night. When I first turn the car on, the AC / auxillary fan cycles on and off - ok, normal, at least for my car. The lights, interior and headlights, dim and the voltage gauge drops when the fan is on.
My question is: does this indicate a bad / dying alternator?
 
Slap, kick, abuse--Year/engine/basics?

Ok, rule of thumb to save your ignition switch in the XJ--turn off ALL accessories BEFORE turning off the ignition switch. That way, the next time you turn on the ignition there will not be a sudden load applied.

Grab a volt meter and check the battery's static voltage between the terminals. Then start the engine and check the voltage again. Should have about 12.5 static, and 13.6~14.5 with the engine running.

Are you sure it is the a/c aux fan cycling--it may be the a/c compressor clutch, especially if the HVAC is set to defrost.
 
fuzzy green groadies on the battery terminals are cause for such things too. Always remove the cables from the battery when cleaning so the connection gets cleaned too, not just the outside of the terminals.
 
joe_peters said:
Are you sure it is the a/c aux fan cycling--it may be the a/c compressor clutch, especially if the HVAC is set to defrost.
Click to expand...

It is a 98 / 4.0 / AW4 / Factory tow package.

Definitely the fan turning on and off, I can hear it from inside the car and watch it with the hood up.
 
Well, two questions:

1. Why is the aux fan running when you turn the engine on? Are you leaving the a/c switch ON when you turn off the engine?

2. Why is the aux fan current draw excessive? Poor motor or a circuit is overloading.
 
I'd assumed the fan was supposed to kick on and off for some reason; I have no idea why. I haven't run the A/C in a long time, it isn't on.
Voltage reads 12.05 / 14.0, engine off and engine on.

Suppose I can check to see what the aux fan is drawing next + try to find a short that is turning it on / off.
What is it supposed to draw for a healthy fan?
 
On a 1998 XJ there are only two normal reasons why the condensor fan will run...
A/C compressor is running and the fan comes on to lower the system operating temperature/pressure (remove the heat of compression) from the air conditioning system OR at approximately 217* coolant temperature the fan comes on to assist in lowering the engines operating temperature.

What temperature does your coolant temperature gauge read?

You state that the operating voltage is 14.0VDC; is that idling or under load?
Operating voltage shouldn't drop below 13.2V with headlights, A/C and in cabin blower motor on.
If it reads below 13.0VDC; you should have the alternator load tested at AutoZone.
You may need a new alternator.
 
Last edited:
ehall said:
The relay could be flipping back and forth on its own... relays go bad sometimes. Swap it with another.
Click to expand...

If the relay is engaging and disengaging due to a weak coil inside the relay that I can understand, but the question still remains.... Why would the ECM energize the grounding wire for the relay ?
 
CharlesS said:
HUH....
for the relay to do anything it has to get signal voltage; false or otherwise.
Click to expand...
voltage is already present. The PCM provides a ground. If the coil is shorting, or the wire from the PDC to the PCM is shorting to ground, the fan will turn on.
 
CharlesS said:
HUH....
for the relay to do anything it has to get signal voltage; false or otherwise.
Click to expand...

Nahhhh ... It happens sometimes ....

The relay internals fail ... and power supply in ( pin #30 ) and power supply out ( pin #87 or #87a ) go closed circuit.

Pin #85 and #86 are signal connections as you said but they are control circuits ... If and when the relay is working correctly.
 
Digger87xj said:
voltage is already present. The PCM provides a ground. If the coil is shorting, or the wire from the PDC to the PCM is shorting to ground, the fan will turn on.
Click to expand...

I understand that there is constant voltage to the relay and the PDC supplies a switched ground for the relay....
Doubt the coil is shorting otherwise the fuse supplying power would have blown already..., but I do agree the ground wire insulation may be worn thru allowing the wire to intermittantly touch a ground source.
There still may be problems causing this issue that are related to false signals to the PCM causing the PCM to switch the relay....
 
I'll swap out the relay for the hell of it, though I looked at the dash and my defrost *was* on, probably has been for months, and I just never noticed. Still not sure why the fan cycles on and off with the defrost blower on... it doesn't do that with the defrost off...

So, new questions.
1. How many amps should the stock e-fan draw?
2. Should the fan cycle on and off with the defrost blowing? If not, should it come on at all?
Again, 98 4.0 113K miles, AW4, factory tow package, blah blah
 
The cycling of the condensor fan is normal when the defrost mode is selected since the AC runs to remove the moisture from the windows and inside the vehicle.
Wouldn't waste your.money on the relay since I am sure the cycling condenser fan is resolved.
The PCM has been receiving a signal from the climate controls to engage the relay and operate the fan.
 
Last edited:
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