Why does SC have 2 speed fan?

sd_iconoclast

Registered User
I have been lokking into the idea of converting the cooling fan on my '89 SC to be run by an external sensor (like alot of other cars), rather than by the ECM. However, I have found that the SC has a two speed engine fan, not just a single speed fan. I have seen lots of posts about how the fan does not come on until over 220 degrees. Does it then run at high speed or low speed? Under what conditions does the fan run at high speed or low speed?
I have read the description of this circuit in the 1989 Thunderbird/Cougar Electrical and Vacuum troubleshooting manual. It describes that two speeds are controlled by the ECM, but it does not say what conditions result in what speeds. Does anyone know the answer?
 
Here's what the Service Manual says about the cooling fan:

The electro-drive cooling fan system consists of a fan and a two-speed electric motor attached to a fan shroud located behind the radiator. The electro-drive cooling fan is wired to operate only when the ignition switch is in the RUN position, thereby preventing cooling fan operation after the ignition switch is turned to the OFF position.

The cooling fan is controlled during vehicle operation by the integrated relay control assembly and EEC-IV module, which will energize the cooling fan under the following conditions:

l) Cooling fan will run at low speed if:

a) Engine temperature is higher than normal. Fan starts running at 106°C (222°F) and stops running at 101°C (214°F).

b) A/C is on and vehicle speed does not provide enough natural airflow. Fan starts running at speeds at or below 69 km/h (43 mph) and stops running at 77 km/h (48 mph).

2) Cooling fan will run at high speed if engine temperature is higher than desirable and fan has been operating at a low speed. Fan starts running at high speed at 109°C (228°F), and stops running at 105°C (220°F).

NOTE: Cooling fan will not cycle with A/C.

The wide-open throttle (WOT) A/C cutout is used on all supercharged engine applications. During hard acceleration, a signal is sent to the ECA. The ECA then signals the integrated relay control assembly to cut off power to the A/C clutch field coil. This keeps the engine from being overloaded.
 
I think that the high speed fan will come on at 230°F and run until speed comes down to about 224°F. I remember seeing something about it in the factory service manual. (Oddly, one of the few things that the EVTM doesn't present in more detail than the FSM.)
 
Here's what the Service Manual says about the cooling fan:

The electro-drive cooling fan system consists of a fan and a two-speed electric motor attached to a fan shroud located behind the radiator. The electro-drive cooling fan is wired to operate only when the ignition switch is in the RUN position, thereby preventing cooling fan operation after the ignition switch is turned to the OFF position.

The cooling fan is controlled during vehicle operation by the integrated relay control assembly and EEC-IV module, which will energize the cooling fan under the following conditions:

l) Cooling fan will run at low speed if:

a) Engine temperature is higher than normal. Fan starts running at 106°C (222°F) and stops running at 101°C (214°F).

b) A/C is on and vehicle speed does not provide enough natural airflow. Fan starts running at speeds at or below 69 km/h (43 mph) and stops running at 77 km/h (48 mph).

2) Cooling fan will run at high speed if engine temperature is higher than desirable and fan has been operating at a low speed. Fan starts running at high speed at 109°C (228°F), and stops running at 105°C (220°F).

NOTE: Cooling fan will not cycle with A/C.

The wide-open throttle (WOT) A/C cutout is used on all supercharged engine applications. During hard acceleration, a signal is sent to the ECA. The ECA then signals the integrated relay control assembly to cut off power to the A/C clutch field coil. This keeps the engine from being overloaded.


That's some good info!
 
The SC has a 2 speed fan because of the current loads necessary to power the high speed winding from a dead stop were too great for the control system being used. The SC controller runs the low speed fan and only turns on the high speed fan after low speed has been running.

The fan motor has two sets of windings in it and both can not be energized at the same time otherwise you risk burning out the fan motor. One set of windings his high speed. The other set is low speed.

The service manual data may be specific to a certain year and may be based on information not firmed up when the car was finally released. Most SC cars do not have an A/C cut out relay. I'm not sure which ones did have it, but I've yet to see it on a car I have owned (89, 90, 93).

Also, the EEC-IV will turn on the low speed fan as soon as the A/C is turned on. It doesn't wait for any specific speeds.
 
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