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Thermostatic Switch

2K views 21 replies 6 participants last post by  EOD Guy 
#1 ·
I used to control my electric fan direct by a toggle switch w/30 amp relay but wanted to alter that a bit and install a thermostatic switch with an overide toggle switch set up. I failed on both ends, scratching my head, and need some help. Here's what I've got or where I'm at:

1. Thermo switch has two male ends on it. I mounted it at the water pump and will note i used plumber tape on threads. Thermo Switch is supposed to activate fan at 185 degrees.
2. I ran relay post 85 ground wire to one prong on the thermo switch. On the second prong of the thermo switch I grounded it to the battery.
3. Get motor up to 200 degrees and the electric fan never came on.

I'm not worried about the override toggle switch at the moment as my first concern is to just get the darn thermo switch to do its job. Any ideas or advice? Did i go wrong somewhere in the above info? Need help. Thanks, Robert.
 
#5 ·
Term 86 hooked to 12V switched source. In my case, wire from relay 86 is hooked to IGN post on fuse block. IE, when i turn key to IGN (not start), the wire is live.
Term 30 is connected to 12V junction block. This wire is fused.
Term 87 is hooked to electric fan
Term 85, ground point on the relay, is as stated hooked to one post on thermo switch.

Chose to install thermo switch on water pump because its going to have hot water like anything else. Installed thermo switch where a heater hose would normally go if someone was running heat. Are you saying the waterpump is not an acceptable part to install thermo switch? Yeah i know the head or intake are customary places, but the water pump seemed just as acceptable to me. If this is not right, let me know. thanks
 
#3 ·
OK If I understand you correctly I drew you a quick crude schematic showing you how to hook up a fan using a 30A relay. A simple on off toggle is all you need to override the thermo switch.

I showed this hooked up from a "switched +12vdc source that should be fused for safety. That way you don't run your battery dead if you leave the override on.

I whipped this up quick so it ain't pretty but it works.
 

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#6 ·
I'll try your diagram. Right off the bat I've noticed your diagram and the way i wired it are different if i'm looking at right:

1. You've got 86 grounded. I've got 86 wired as a 12v switched source.
2. If i'm looking at diagram right, i'd say you've got pin 30 acting not only as a 12V source, but also serving as a 12V switched source via a 'jumper wire,' correct?

Question: Looking at your diagram, on the override toggle switch, I assume the 'IGN SW' wire goes to the power prong of the toggle switch? Thanks RIPVW
 
#4 ·
Rip VW it is a great drawing, and why I asked what is connected at #86 on the relay.

I suspect #86 is grounded (as in your drawing) and the thermo switch needs to be powered (+12). If #86 is grounded, then the toggle switch (by-pass) is most likely powered (+) and if so if the toggle is turn on while the thermo switch is still grounded sparks will fly.

However, if 86 is powered (+12), then of course the by-pass switch is grounded like the thermo switch and all is good electrically. Which takes us to where the thermo switch is install and why I asked about the water pump location.
 
#7 ·
You can always just jumper the switch or sensor just to see if it works or your circuit idea is correct. Of course be careful with this when working around anything computerized. I attached a couple of pics I found on the web and a quick schematic that I put together. OEM is good about putting switches and sensors in the intake manifold or water outlet. Depending on where you put your switch it might be ok but as the pics show, you want to measure the temp of the water in the jacket. On the side of the head area "C" as shown by the arrow would be where you would place the switch. If your head doesn't allow this, then you have to go to the intake crossover at the front of the manifold or the outlet. It also might be the case where you want to turn on the fan at 180, use a 165 or etc... Some of it is still trial and error, but better than ruining the engine. In my diagram I added a fail safe switch if the automatic function doesn't work, you still can turn the fan on from the dash.

Not knowing exactly the composition of your switch, I am assuming the temp sensitive wax or expanding wax pellet like the thermostat. When the wax gets to the temperature identified it becomes soft enough that it allows the switch to close or expands closing the switch. As it cools down the wax hardens or retracts and breaks the connection. Of course it could be a bi-metallic spring, or thermistor, but not very likely.


The single spade switch is a grounding style and the 2 spade style is the non-grounding style. You can use either one, but you need the proper circuit for it to work properly. If your putting the switch into the head, I suggest use it as a trigger on the ground side, just in case the insulation ever melts and grounds out. Of course every thing should be fused, but just in case I would use it for a ground side trigger.


www.pegasusautoracing.com/productdetails.asp?RecID=10284


You can put the non-grounding style on either side of the fan motor, ( 12+ or 12- ), but the grounding style needs to be on the ground ( 12- ) side of the circuit.


First check the ohms between the spades when the engine is cold, it will should either 0 or infinity, when the engine hits the specified temperature, it should be the opposite if the switch is working. You can also just test it by placing it in a pot of water on the stove as you don't want to risk damage to the engine. Test it by starting with room temp water and heat it in the pan, watch the thermometer, and watch the ohm meter at the same time. Using alligator clip jumpers and a kitchen meat or candy thermometer works good for this.


In experience, I had a friend that his temp sensor failed on the way back from a car show, he wired the relay input to the head light wire on the side of the road. This way he turned on the headlights after starting the engine, kept the fan running and made it home with damaging the engine.
 

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#11 ·
The single spade switch is a grounding style and the 2 spade style is the non-grounding style.

I think that is where i went wrong today (treating the 2 spade switch as if it was a one spade) and appreciate the information:) I've got some different wiring diagrams now from these posts, but all roads lead to supplying 12V to the thermo switch. Will give it a go, tinker some more, and see what happens
 
#8 ·
Your wiring is OK, it really doesn't matter which side of the relay coil you ground (unless relay has a diode), so long as everything is wired accordingly.

The problem is where you have the thermo switch installed, move the thermo switch to the intake or head. The heater ports at the water pump are a poor choice for the switch. The water pump is usually on the input of the motor's coolant path (cool side), which can be 20-30 degrees cooler than the output (hot side of the motor). The intake or head would be a better placement for your thermo switch as they are on the output (hot) side of the motor's coolant path.
 
#9 ·
will do 36Sedan. I'll move the thermo to intake or head and tinker with the wiring some more as in, according to RIP's post, he showed the relay actually grounded to metal and 12V going to thermo switch. If it does not matter which side i ground the relay then i'll deviate a bit from RIP and use the 85 pin as straight ground and run 86 pin wire to thermo.
 
#10 ·
Your wiring is OK, basically you're doing the same thing as Rip's drawing, you're just switching the ground (-) instead of the hot (+). Function wise it accomplishes the same thing and some prefer to switch the ground rather than the hot, it really makes no difference. Move the thermo switch and you should be working as designed.
 
#12 ·
I ran relay post 85 ground wire to one prong on the thermo switch. On the second prong of the thermo switch I grounded it to the battery.
As you wrote above will work OK. Your switch is isolated contacts and can be used to switch the ground by grounding one terminal or hot by wiring it to positive. The single terminal type switch has one contact internally grounded and can only be used to ground.

As long as you have one terminal on the thermo switch grounded and the other terminal going to the relay, you're fine.
 
#13 ·
There actually is an advantage to having the relay switch by ground, rather than by positive.

The wire going to the motor is exposed to vibrations, moving parts and substantial heat. If the circuit is switched to ground it will be less susceptible to causing damage due to a short caused by wear and heat. The ground side of the relay carries very little current and a wire attached to this side will usually cause no damage if shorted (no smoke, no fire). In the event of an insulation or wire breakage it either does not operate the relay (open wire) or the relay stays on (wire grounded). Either way it will not cause the damage a positive wire will when shorted.

Relays are usually not attached to the motor so the chance of the hot wire failing going to the relay is much less likely and is why most automotive relays operated by motor controls are ground switched.
 
#14 ·
NOTE****

The Relay I use in this drawing is the following type relay. It is a Pro Link SPDT Relay as follows: Single pole double throw automotive type relay. Integrated plastic mounting tab. 5 terminals. 40 Amp rating on the normally open contact and 30 amp on the normally closed contact. Manufactured to strict ISO standards.

On the relay 86 and 85 are the terminals that activate the relay.

One terminal gets +12Vdc

The other terminal is grounded.

** Note a damping diode could be added to this relay and the diode would help keep switching spikes in check. make sure the anode is on ground and the cathode (stripe on Diode) on your + switching leg pins 85 and 86.

It doesn't matter electrically which pin 85 or 86 is hot and which is ground. There is most likely a spec called in the automotive industry. I never really used a specific pin as most uses I have used this relay for I just used it as a replacement and that is usually plug and play. just if you use the clamping diode then the cathode must go to the pin you select for the +v ie 86~85.


Not having exact facts like how yours was wired I made some basic assumptions

1. I assumed your thermo sensor having 2 terminals was simply a SPST switch, ( Volts go in 1 terminal and when the thermo gets above ~ 180 deg you get volts at the other terminal). To test this take an ohmmeter and measure between one terminal and the other.

At room temp you should show NO continuity between the terminals.
Next is place the sensor into a pan of boiling water and keep in in there at least a couple a minutes or more. Next pull the sensor out of the water and quickly put the ohmmeter on the two terminals and they should then show continuity.

**My definition of continuity is a low Ohm reading of say less than 1 ohms.

***My Definition of open is anything that does not fit in the previous description.

When your temp goes below ~170 the thermo opens and disconnects the voltage to the Fan motor. When the temp rises the whole cycle repeats.

2. I know some manufactures like to use a switched ground But I prefer the simpler method of switching the hot side.

3. The override switch just puts 12Vdc on the relay to activate it if you want to switch it on at any temp below the thermo switch limit.

4. Pin 30 on the relay is the terminal to use for the source voltage to fan. Think Big heavy wire NOT 18ga.

5. Pin 87 will be the terminal that goes to the fan Hot wire.

6. Pin 87A is not used at this time.

7. I assumed your fan having 1 wire to feed it and an internal ground.
If you have 2 wires going into the fan motor determine which wire needs to be hot, and the other should go to a good solid vehicle ground as close to the fan as possible to eliminate ground noise.

As I said that drawing was just a crude quick scribble in Paint and may not be in the best form. I may not have drawn my connections properly but electrically it is correct!

I will say If the assumptions are true then I guarantee it will work.!

Oh crap it is 11PM and I should be getting my beauty sleep so see all of you in the morning... "Late" :cool:
 
#15 ·
Some complicated answers to a simple problem, you have pretty much figured it out.

As stated above..... relays don't care which terminals get pos or neg as long as the circuit is consistent. Using neg or pos to trigger the relay does't matter .... again as long as the circuit is consistent. Finding a spot in the water jacket to place the sensor, some are hotter that others etc........ with a fan controller, you can compensate for the temp differential, regardless of where you put the sensor or using a two blade vs single blade to over come a poor ground issue etc.....

Bottom line you need to assess your set up and come up with what works for your vehicle.

Most diagrams can be switched to accommodate neg/pos switching, single or dual pole sensors etc....
 

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#16 · (Edited)
Rip VW, your drawing is perfect, I'm sorry if I insinuated otherwise, and I certainly meant no disrespect to you sir.

I was trying to let the OP know that his problem was more caused by his thermo switch placement than the wiring. Sometimes I go a little overboard. And, you are correct your drawing will work 100%. No argument from me on that.

Hopefully the OP moves his thermo switch an the problem is solved.
 
#17 ·
Type of thermo switch

I'm laying out my wiring harness this winter for a 36 Chevy Build and was curious to know what thermo switch you are using. Will make my life a little simpler to know what to ask for at the parts store and lay out the right wiring for a two pole switch.
Thanks.
 
#18 ·
36Sedan and RIP, wanted to say thankyou for the advice and diagram you gave me. Moved the thermo switch to the head, wired it pretty close to RIP's diagram and everything worked. Fan kicked on when it was supposed to, fan kicked off when supposed to, and override switch works.:D

Zooma, I used part #30111 by Painless, thru Summit, for the thermo switch. Don't know at what degree you're wanting to kick the fan on, but this one's trigger is at 185 degrees. As to wiring, if you want to know how I did it, just shoot me a PM. Will say i basically wired it pretty similar to RIP and 36Sedan's input.
 
#22 ·
The controller does that and more...... In the test mode it allows the fan circuit trouble shooting. You can adjust the on/off to any temp you want, one or two fans etc.......

A buddy had one and I liked it..... I switched from the old sensor, relay and bypass switch and have zero regrets.
 
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