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Unread 04-09-2013, 07:26 AM   #1
CJ7KAHUNA
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Can someone explain this fan switch for me?

I am trying to find a 2 stage fan control switch that will mount in a 4.0 tstat housing. In one of the many Contour fan swap threads I ran across a post that stated that BMW utlizes a switch that operates on this principle. I looked it up and its a 3 terminal/wire switch.

It has 3 terminals labled - 0, T1 and T2. I assume that T1 and T2 are low and high speed control and 0 is either 12v or ground depending on how you plan on making your relay. Would this be correct?

bmw-temp-switch.jpg  
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Unread 04-09-2013, 08:50 AM   #2
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That is made to work in conjunction with a switching relay that works with a two speed fan, when one of the positive leads is active the other lead is inactive. They are commonly used with the Volvo switching relays and the Ford Tarus 3.8L fans to set the fan speed from low speed to high speed.
Another thing you must be aware of is the BMW switches are metric threaded wheras your 4.0 housing is SAE threaded so you will have to have an adaptor to run it.

Here is how you set that temp sensor up.
http://www.nastyz28.com/forum/showthread.php?t=200028
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Unread 04-09-2013, 11:42 AM   #3
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Quote:
Originally Posted by markso125 View Post
That is made to work in conjunction with a switching relay that works with a two speed fan, when one of the positive leads is active the other lead is inactive. They are commonly used with the Volvo switching relays and the Ford Tarus 3.8L fans to set the fan speed from low speed to high speed.
Another thing you must be aware of is the BMW switches are metric threaded wheras your 4.0 housing is SAE threaded so you will have to have an adaptor to run it.

Here is how you set that temp sensor up.
http://www.nastyz28.com/forum/showthread.php?t=200028
Correct me if I am wrong but what I am getting from looking at that diagram is that both relays have a constant 12v feed and that the temp switch is breaking the ground to either the high or low speed relay depending on demand. Is this correct? If that is the case then the Volvo relay is optional and it would be simple enough to wire up using individual components.

Assuming this is the case - can you tell me if I am identifying the pins on the temp switch correctly? Is T1 low speed, T2 high etc?


As for fitting the 4.0 housing - Here is a possible solution depending on the 4.0 housing hole diameter and thread pitch. If its at least 3/8 NPT this or something similar would work:

http://www.jagsthatrun.com/Pages/Par...mpSending.html
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Unread 04-09-2013, 12:20 PM   #4
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Yes the temp guage is switched you only can run one fan at a time through that temp sending unit.
The reason why you use the volvo fan switching units is you have the relay built into it already so that reduces some of the clutter but also you dont have to put as much amperage through the temp sending unit itself, the volvo units are pretty cheap they were installed on alot of volvos in the 90's the most common one is the 850, you can get the units for about $45 new and buy used ones on ebay for about $20
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Unread 04-09-2013, 12:50 PM   #5
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Shoot, now there's another car to look through on my next junkyard trip! Thanks for the link.
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Unread 04-09-2013, 03:20 PM   #6
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Quote:
Originally Posted by markso125 View Post
Yes the temp guage is switched you only can run one fan at a time through that temp sending unit.
The reason why you use the volvo fan switching units is you have the relay built into it already so that reduces some of the clutter but also you dont have to put as much amperage through the temp sending unit itself, the volvo units are pretty cheap they were installed on alot of volvos in the 90's the most common one is the 850, you can get the units for about $45 new and buy used ones on ebay for about $20
The Cougar/Contour factory wiring design has both fans running in both low and high speed. Low speed is routed through the resistor and high speed simply bypasses the resistor. The way I intend to wire mine the only amperage load the switch will carry is what ever is required to operate a relay. The relay itself will carry the fan load.
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Unread 04-09-2013, 03:33 PM   #7
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I think that should have read that the temp gauge is switched so you can only run one speed at a time, considering that as the nastyZ28 thread was pertaining to Taurus fans which only have one fan.
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Unread 04-10-2013, 01:36 PM   #8
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Originally Posted by CSP View Post
I think that should have read that the temp gauge is switched so you can only run one speed at a time, considering that as the nastyZ28 thread was pertaining to Taurus fans which only have one fan.
yes thank you for catching my brainfart

I did mean that it can only run one speed at a time.
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Unread 04-12-2013, 06:42 PM   #9
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Quote:
Originally Posted by CJ7KAHUNA View Post
Assuming this is the case - can you tell me if I am identifying the pins on the temp switch correctly? Is T1 low speed, T2 high etc?
According to this schematic, it's the other way around. T1 is high, T2 is low.
bmw-temp-switch.jpg  
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Unread 04-12-2013, 09:07 PM   #10
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Originally Posted by SLO_Ken View Post
According to this schematic, it's the other way around. T1 is high, T2 is low.
Thanks for posting that. What year and model is that schematic from? I would like to find the female connector for that Temp switch. Best I could find was mid 90's 328i. Havent found the connector yet though.
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Unread 04-12-2013, 09:41 PM   #11
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Originally Posted by CJ7KAHUNA View Post
Thanks for posting that. What year and model is that schematic from? I would like to find the female connector for that Temp switch. Best I could find was mid 90's 328i. Havent found the connector yet though.
Not sure... I took it from the nastyz28 forum thread linked in post #2.

From that same thread, here's a list of part numbers.
http://www.nastyz28.com/forum/showpo...&postcount=123
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Unread 04-13-2013, 12:38 AM   #12
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The "O" terminal is common.

"T1" is the Low Speed (or Low Temperature) trigger contact.

"T2" is the High Temperature/High Speed trigger contact.

Check the operation of the switch before you commit any wiring (this may be done with a pot of water & a stove,) some applications have T1/T2 as two isolated circuits, others have Switch Open/T1/T1+T2 - and you want to make sure before you wire it up.

If the original application is a single electric fan with dual windings, the two trigger circuits are usually separated. If you have two electric fans, the circuits are usually tied together - "Low Speed" being a single fan running, "High Speed" being both fans running.
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Unread 04-13-2013, 12:56 PM   #13
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Quote:
Originally Posted by 5-90 View Post
The "O" terminal is common.

"T1" is the Low Speed (or Low Temperature) trigger contact.

"T2" is the High Temperature/High Speed trigger contact.
0 being common I assume that means that what ever source is fed to that terminal, be it either 12v or ground, will be what is fed to either T1 or T2 as temp demand requires. According to the diagram above - it seems to be the other way around with T2 being low and T1 being high. Am I not understanding it correctly?

Quote:
Check the operation of the switch before you commit any wiring (this may be done with a pot of water & a stove,) some applications have T1/T2 as two isolated circuits, others have Switch Open/T1/T1+T2 - and you want to make sure before you wire it up.
Being ths feed is coming from a single 12v source would it matter if for some reason both T1 and T2 were made at the same time? I assumed that it would make no difference. I figured that the lowspeed function would sort of act as a start assist for the high speed since the fans blades are already turning reducing drag when the high speed is activated.

Quote:
If the original application is a single electric fan with dual windings, the two trigger circuits are usually separated. If you have two electric fans, the circuits are usually tied together - "Low Speed" being a single fan running, "High Speed" being both fans running.
The original application is both fans running in both low and high speed. The low speed voltage is wired through a resistor and the high speed just bypasses the resistor.
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Unread 04-17-2013, 01:43 PM   #14
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Originally Posted by CJ7KAHUNA View Post
Being ths feed is coming from a single 12v source would it matter if for some reason both T1 and T2 were made at the same time? I assumed that it would make no difference. I figured that the lowspeed function would sort of act as a start assist for the high speed since the fans blades are already turning reducing drag when the high speed is activated.
No you dont want both high and low speed running at the same time, this is very dangerous and can cause a fire, basically what you are doing is the low speed portion of the motor is holding the high speed portion of the motor up(or vise versa) thus causing excessive heat and damage to the fan unit causing fans to short circuit ect ect. Think of it like taking a small coordles drill you screw the chuck all the way in and run the drill on the lowest speed now you grab onto the chuck and hold it so it doesn turn, now either the clutch in the drill itself will kick on or it will slow down and get hot in both your hand and the drill itself will start to get hot... basically you would be using one force(your hand/the low speed fan voltage) to hold the chuck(high speed fan) back.

Thats why the volvo box is so popular for all automotive applications(heck I think it is the only swap more common then an LS motor), when those electric fans off of the fords were originally installed on cars the ECU controlled the fan speed within the required paramaters, shutting down the low speed and then starting up the high speed as needed, but the volvo box is basically a switching relay it turns off the low speed fan when the high speed fan is active thus not allowing both high and low speed to run at the same time.

Quote:
Originally Posted by CJ7KAHUNA View Post
The original application is both fans running in both low and high speed. The low speed voltage is wired through a resistor and the high speed just bypasses the resistor.
Yes but the fans are controlled through the ECM on the car and allows the high speed of the fan to kick on at either extreme temperature levels or when the AC unit kicks on.
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Unread 04-18-2013, 08:20 AM   #15
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Originally Posted by markso125 View Post
No you dont want both high and low speed running at the same time, this is very dangerous and can cause a fire,.
If I understand this part of your previous post correctly both will not be running at the same time:

Quote:
Originally Posted by markso125 View Post
That is made to work in conjunction with a switching relay that works with a two speed fan, when one of the positive leads is active the other lead is inactive


The way that reads to me is that only one - either the low or high speed lead is active at any one time. This being the case you can simply have the low speed lead energize the a relay bring in the low speed at temp and when the demand calls for it - this relay will drop out and the high speed will kick in. Unless I am not understanding the switch correctly and both high and low speeds are energized at the same time.

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Originally Posted by markso125 View Post
basically what you are doing is the low speed portion of the motor is holding the high speed portion of the motor up(or vise versa) thus causing excessive heat and damage to the fan unit causing fans to short circuit ect ect.
Is there a high and low speed portion of the motor? The way I understand it is that the motor has a single lead for power going in. If the power feeding that lead is reduced the speed is reduced proportionately. If the power is a full 12v the fans run at full speed. Unless I am missing the boat the fan motors do not have dedicated windings or portions that are dedicated to certain speeds.

What I am not sure of is if you have 12v going through the resistor circuit reducing the voltage and it meets a full 12v provided by the high speed relay on the other side of the resistor how or if that would affect the full 12v load for high speed. I am pretty sure that beings its coming from a single 12v source you wont increase or multiply voltage.


All of tht being said - what i would like to do is simply feed a 40 amp relay for the low speed circuit off of T1 and have T2 feed a 70 amp relay to bring in high speed as demand requires. Ideally T1 and T2 will not be energized at the same time. But even if they are I am not sure how much of an issue that will be to the motors.
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