Mark VIII High/Low Question

[JoshMcMadMac]

I am hoping somebody here might know this one. With the Mark VIII fans, they have a high and low connection. When the high lead comes on, does the low stay on as well or do they "alternate" so that only one of the two gets voltage at the same time?

 

[driller]

The Mark VIII fan is a variable voltage fan. One wire is not used and terminates in the harness. The VCRM starts the fan at 50% voltage and ramps up to 100% voltage according to the PCM.

 

[JoshMcMadMac]

The Mark VIII fan is a variable voltage fan. One wire is not used and terminates in the harness. The VCRM starts the fan at 50% voltage and ramps up to 100% voltage according to the PCM.

You are telling me that they went through the trouble of adding a third connector and wire, just for it to terminate in the middle of nowhere for no good reason? Don't get me wrong, I know you know your stuff, I just do not get it.

 

[Jeffguy11]

ive been thinking about wiring a switch to the fan for the track..if i could leave it on during the wait it seems i could make better use of my 160 t-stat. Sounds like this isnt possible tho after reading this post

 

[driller]

I use a cooling fan over-ride at the track...

Blue = + voltage from VCRM.

Outside black = ground

Middle = no connection

 

[turborich]

I use a cooling fan over-ride at the track...

Blue = + voltage from VCRM.

Outside black = ground

Middle = no connection

Driller, Since I have no idea of how to follow that drawing, could you please explain it in a way that dumb people could understand it? I would like to install an over ride switch as well.

Thanks.

 

[Battery]

Driller, Since I have no idea of how to follow that drawing, could you please explain it in a way that dumb people could understand it? I would like to install an over ride switch as well.

Thanks.

Thanks for asking that so I can see too without having to call myself a dumb person.

 

[driller]

I use a cooling fan over-ride at the track...

Blue = + voltage from VCRM.

Outside black = ground

Middle = no connection

OK - you need a 40 amp relay - called "R1" in drawing.

If you know relays - you want a SPDT type. The common terminal is "C" and the normally open terminal is "NO" and the normally closed terminal is "NC". All that means is that with no power to the coil of the relay, the relay is normally closed alloing power from the VCRM to go to the fan.

When power is applied to the coil of the relay, the normally open contacts close and power is applied from the battery.

F1 and S1 are simply a fused switch to power the relay on/off from a power source that is hot with the IGNition on. The other coil terminal is the ground.

CB is a 40A circuit breaker to prevent fires.

Basically you are putting a "switch" using a relay inline with the power wire to the cooling fan. When the relay is off, the fan operates as normal. With the relay on, you are putting full battery power to the fan making it run at high speed.

 

[JoshMcMadMac]

Hey JP (or anyone), about that third connection to nowhere? These fans were exclusive to the Mark VIII, right? So why is the third connection there?

 

[driller]

According to the '96 T-bird manual...

Constant Control Relay Module

WARNING:
DISCONNECT THE COOLING FAN MOTOR PRIOR TO PERFORMING ANY UNDERHOOD SERVICE SINCE THE COOLING FAN MOTOR COULD CYCLE IF THE IGNITION SWITCH IS LEFT IN THE ON POSITION EVEN THOUGH THE ENGINE IS NOT RUNNING.

Note:
Cooling fan motor will not cycle with A/C clutch (2884). The cooling fan motor will come on when A/C switch is turned ON.

The cooling fan motor is controlled during vehicle operation by the constant control relay module (CCRM) (12B581) and powertrain control module (PCM) (12A650), which will energize the cooling fan motor under the following conditions:

Cooling fan motor will run at low speed:

l if engine temperature is higher than normal. Cooling fan motor starts running at 106°C (222°F) and stops running at 101°C (214°F).

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

Cooling fan motor will run at high speed:

l if engine temperature is higher than desirable and cooling fan motor has been operating at a low speed.

l at 109°C (228°F) and stops running at 105°C (220°F).

The same year Mark VIII...

Variable Load Control Module

The variable load control module (VLCM) controls:

l the cooling fan motor operation and speed.

l the A/C clutch operation.

l other non-A/C functions.

l It also increases and decreases the cooling fan motor speed as necessary, depending on the refrigerant system high-side pressure.

l Turns the A/C clutch circuit OFF if the high-side pressure exceeds 2930 kPa (425 psi).

I don't know but I suspect the fan is actually the same, it is the control that is different? But the Mark VIII fan is renowned for it's capabilities whereas you don't hear the same of the T-bird fan? I suppose one would have to have one of each for bench testing to confirm.

 

[JoshMcMadMac]

According to the '96 T-bird manual...



The same year Mark VIII...



I don't know but I suspect the fan is actually the same, it is the control that is different? But the Mark VIII fan is renowned for it's capabilities whereas you don't hear the same of the T-bird fan? I suppose one would have to have one of each for bench testing to confirm.

Great information, JP. The fans look the same, but have different part numbers. I suppose I need to find one at the yard and rig it up using the inner and outer connections to see what it does or does not do. I know that I have seen Mustang guys connect a Mark VIII fan with a relay, making it an on/off circuit, so I suppose it works fine under both circumstances...it is just a shame to bypass the nice variable-speed feature.