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Old 11-07-2009, 07:39 PM   #1
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Default Testing Thermoswitch on 93 1.6

Fortunately there were enough cooling fan threads to make me think that something is wrong with my thermo-switch(s). I want to post because of the plural.

I can ground out the thermo-switch connector and my fans come on. My coolant temp was up to 240F based on Tunerstudio value.

The problem is that I tried two different thermo-switches and both didn't turn on the fans.

What is a good method for testing the thermo-switches? Could I make a simple circuit with a 9v battery, lower the switch into boiling water, and see if I notice voltage drop as the temp climbs?

Based on my searching it appears that it can only be the switches. I couldn't imagine a temp difference of 40F between the front and rear temp sensors unless my thermostat wasn't opening. However it did appear that the coolant was moving when I ran it with the rad cap off.
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Old 11-07-2009, 08:03 PM   #2
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Not that this helps you, but I believe this is why my fan turns on with a switch. I had my doubts about the thermo switch, so I route 12v to the fan with a relay in the middle, switch turns the relay on/off.
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Old 11-07-2009, 09:20 PM   #3
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Quote:
Originally Posted by djp0623 View Post
Fortunately there were enough cooling fan threads to make me think that something is wrong with my thermo-switch(s). I want to post because of the plural.

I can ground out the thermo-switch connector and my fans come on. My coolant temp was up to 240F based on Tunerstudio value.

The problem is that I tried two different thermo-switches and both didn't turn on the fans.

What is a good method for testing the thermo-switches? Could I make a simple circuit with a 9v battery, lower the switch into boiling water, and see if I notice voltage drop as the temp climbs?

Based on my searching it appears that it can only be the switches. I couldn't imagine a temp difference of 40F between the front and rear temp sensors unless my thermostat wasn't opening. However it did appear that the coolant was moving when I ran it with the rad cap off.
It is just a snap switch that closes to ground on temp rise. A simple circuit with a battery and bulb would test it. If you have done a reroute and moved the switch/housing location, make sure the housing is grounded.
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Old 11-08-2009, 07:34 PM   #4
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I bought a new thermo switch and no luck. I then bought another thermostat since mine wasn't opening to my liking. This also didn't work.

It turns out that my fan relay worked when I was diagnosing the problem and that was it. That's right. The one time I used it to troubleshoot the system it worked.

Out of desperation I grounded the thermoswitch again. Nothing but a faint click coming from the box where the fan relay resides. I'll buy a new relay tomorrow. Autozone seems to carry a generic that is $16. Advance has one for $25
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Old 11-08-2009, 07:37 PM   #5
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Welcome to the club. I've had the same problem since I swapped motors.
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Old 11-08-2009, 11:13 PM   #6
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if you ran MS you wouldn't even need that thermo switch sensor in the front
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Old 11-08-2009, 11:26 PM   #7
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I don't have enough outputs to run the fan on my diypnp. I've used them all. When the output adapter board comes out I will probably have the pnp control the fan.
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Old 11-09-2009, 12:53 AM   #8
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Quote:
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if you ran MS you wouldn't even need that thermo switch sensor in the front
That's what everyone tells me, but my fan doesn't work on my 1.6 chassis with MSpnp.
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Old 11-09-2009, 09:57 AM   #9
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Does anyone know off hand the current draw from the ac and cooling fan? The previous owner wired them in parallel. I am going to replace the 10A relay, but if the current draw exceeds the relay limit then I need to fix that before I start replacing expensive relays.

Last edited by miatauser884; 11-09-2009 at 02:37 PM.
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Old 11-09-2009, 02:18 PM   #10
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Quote:
Originally Posted by djp0623 View Post
Does anyone know off hand the current draw from the ac and cooling fan? The previous owner wired them in series. I am going to replace the 10A relay, but if the current draw exceeds the relay limit then I need to fix that before I start replacing expensive relays.
They need to be in parallel
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Old 11-09-2009, 02:37 PM   #11
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They need to be in parallel
They are wired parallel. I don't know why I put series. I will edit the post. What amperage are both fans drawing?

5.3 to 6.5 amps from cooling fan: http://www.miata.net/garage/CoolingSystemProblems.html
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Old 11-11-2009, 10:54 AM   #12
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I ordered a new relay, installed it, then grounded the thermoswitch connector. It works. The relay is listed under the horn relay at advanced auto parts. I'm still concerned that the amperage draw of both fans exceeds the 10A rating for this relay.

Any part numbers for a similar relay except 15A instead of 10A?
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