Resistor on radiator fan pigtail

[diambo4life]

Can someone explain the function of this resistor looking contraption? I am trying to wire aftermarket fans and I was wondering whether I can get rid of this "thing." But first, I need to understand its purpose. Thanks for your feedback.

 

[JC SSP]

I believe it’s for the high & low fan settings but I will default to others with better electrical experience.

 

[Robert Larimer]

Can someone explain the function of this resistor looking contraption? I am trying to wire aftermarket fans and I was wondering whether I can get rid of this "thing." But first, I need to understand its purpose. Thanks for your feedback.

It is a resistor that gives you a low speed fan. Removing it will cause the fan to run at high speed all the time. If they burn out the low speed fan does not come on at all. Most aftermarket fans units include the resistor. I do not know if fans are made to run on high all the time.

 

[Pentalab]

If the resistor burns out, it was not sized correctly to begin with....(wattage wise) Basic electronics 101.
The resistor is there as a cheap and dirty way to lower the speed of the fan. The current flowing through the resistor creates a Voltage drop across the resistor. I measured 14.75vdc across the battery terminals....(eng idling) With the resistor in the circuit, the measured Vdc across the fan is a lot less. A relay shunts out the resistor for full voltage / max speed ) aka high speed).

If the fan won't handle continuous high speed operation, it too is not designed correctly.

 

[diambo4life]

I never really paid attention to how the stock fan operated. So , did it operate at low speed ALL the time and only switched to high if it got hot?

I am also contemplating running them off a thermosensor as well if I do eliminate that resistor. Any opinions?

 

[Pentalab]

I never really paid attention to how the stock fan operated. So , did it operate at low speed ALL the time and only switched to high if it got hot?

I am also contemplating running them off a thermo sensor as well if I do eliminate that resistor. Any opinions?

Nope.

Start car. On idle in the driveway, low speed fan kicks in at aprx 204 F, then drops out when temp is down to 194 F. Then it heats back up to 204 F, and low speed fan kicks in again. The cycle just repeats. When going down the road at 30 mph, there is enough air through the rads, the low speed fan never kicks in. If it's a hot day, and u are sitting at a red light, then maybe the low speed fan will kick in.

High speed fan threshold, (I think) is aprx 215 F.

I can set the threshold temps for the low speed fan over a wide range on my SCT-X3 hand held tuner. Same deal with the high speed fan threshold temp, a wide range can be dialed in.

When VMP tuned the car, I had em used the OEM low / high thresholds.

In normal operation, the high speed fan will never kick in.

 

[diambo4life]

Thanks for that response. So eliminating the resistor = fan running on high all the time or during that specified window ie. 204+. Once the car is running, I will try it and see and make a final decision how I want it to operate.

 

[Pentalab]

Thanks for that response. So eliminating the resistor = fan running on high all the time or during that specified window ie. 204+. Once the car is running, I will try it and see and make a final decision how I want it to operate.

yes, u could eliminate the resistor, then when the fan does kick in ( at a given threshold)..it will come on at max.

With the oem lower fan threshold ( 204 F)..and no resistor used, the fan will kick in..on high speed..and just cool it back down to 194 F a lot faster vs low speed fan. It would work good..and get the temp back down quicker. With the fan on high speed, it would take less time to cool it down to 194 F.... so although the fan is operating faster, it's on for less time.

 

[Robert Larimer]

Thanks for that response. So eliminating the resistor = fan running on high all the time or during that specified window ie. 204+. Once the car is running, I will try it and see and make a final decision how I want it to operate.

The fan runs continuously on low if your AC is on to cool the evaporator. If you do not have low speed the compressor pressure will rise and kick the high speed fan on until it reduces regardless of engine temp. It will cycle like that continually. I do not recommend that option if you use your AC. It is hard on the compressor and the cycling is quite noticeable and annoying. I guess you could have the fan run continuously on high when the AC is on but that will stress the fan motor. When my resistor burnt out I found that I could buy an entire new fan assembly with the resistor included for about the same price Ford charges for a new resistor so I went that route and have had no problems for years.

 

[diambo4life]

Thanks very much for your input guys!!!!

 

[JC SSP]

I use a GT500 fan with 170 degree thermostat. I adjusted the high and low temp setting via my tuner.

I am assuming since the fan is aftermarket it has a temp sensor/probe to activate it. Just set the on/off temp to your desired temp (e.g., 190) and you should be good to go.

 

[diambo4life]

The aftermarket fans just have + and - with no controller. So I have to use the ECU to control them which I will. I am running an aftermarket ecu in this car so I do have options. In my other car, the radiator is controlled by a thermo switch so ECU control is not needed at all. It's an option I have in my bag.