Does one need the FC Thermoswitch when running a PFC? Can't the datalogit just adjust the temperature down manually? If so what's the rationale for using the FC thermoswitch with the PFC?


Thoughts?

 

You can make the fans come on nearly whenever you like with the pfc and datalogit so not needed.

 

cool.. saves me 70.00

 

Ihor is right,, no need to waste money on it.

 

what you have to understand though is that the thermoswitch increases the speeds of the fans by grounding another relay, which in turn supplies power to additional terminals on the two fans. An FC thermoswitch will trigger medium or high speed at a lower temperature. I understand why people would say it's not necessary, but it's not useless either.



There are 4 relays which control the fans up to 3 speeds. Each fan receives juice on 3 different pins on the connector, with the 4th pin being a ground. 2 relays are switched by the ECU/PFC, and will supply power to the "B" terminal on each fan. That will put the fans on low speed. One relay is switched by the thermoswitch which is wired such that it triggers the "D" terminals and raises fan speeds to medium. Finally, the last relay is switched by the A/C and puts power on the "A" terminal on the fans. The three terminals on the fan don't need to be triggered in any order really. That's why just putting on the A/C can turn on the fans even if the ECU/PFC hasn't switched them yet.

With an FC thermoswitch and proper PFC configuration your fans will ramp their speed up in the stock manner, but do it sooner. This helps cooling while still keeping the fans from drawing more power than necessary or causing increased wear on the fan motors. The thermoswitch also affects the aftercooling function in the cooling fan control module, presumably increasing the likelihood that the fans will run for 10 minutes after you shut the car off. Although the FC thermoswitch is not "needed" in the strictest sense, it would help the cooling of the car both with the engine running and when it shuts off.

The FC thermoswitch is what, 95 C? Something like that. So you can trigger your PFC for low speed at 87 C, then get medium speed at 95C. Or if the A/C is on, that will trigger low speed. Then the PFC will bump it up one speed, and then the thermoswitch will have it running at max speed by 95 C or whatever the temp is. And the aftercool function will work more frequently in the summer for when you shut the car off at a gas station or something. You can see that the logic circuit for the aftercool function is based in part on whether the thermoswitch has been triggered or not.

 

thanks for the post, arghx. Good information there... I'll sleep on it!

 

Scratch my original comment. I was wrong about the Miata switch.

Search is a wonderful thing

https://www.rx7club.com/showthread.p...=miata+thermo*
https://www.rx7club.com/showthread.p...=miata+thermo*

 

Just to reiterate. You DO need the thermoswitch to get to higher fan speeds at lower temperatures! The PFC DOES NOT do this alone. I believe this has been covered many times in previous threads.
--Jeff

 

That is true but if the temps continue to climb the fans will kick up a speed anyway. If you're going to get a new switch, then might as well get a FC switch. They do go bad with age so I like to replace them during rebuilds. The power FC base map will turn the fans on at about 100C, vs 108 stock. With the datalogit you can program it to come on whenever you want. You can't access this through the commander alone.

 

^This is what I did.
I already had a PFC and the old "Miata" thermoswitch when I did my rebuild. On reassembly I simply replaced it with a new FC Thermoswitch since it didn't seem to make sense messing with the FD version....and they're the same price. But if I didn't have an obvious occasion to be in there anyway, I certainly wouldn't have bothered otherwise.

 

What temp does the stock FD thermoswitch come on at?

If you turn the fans on with the pfc at 86c temps generally stay lower just by addressing the heat sooner. Provided your temps don't keep climbing there is no need for higher fan speeds. Upgrading the radiator, closing any gaps around the radiator and making sure the undertray is installed will go a long way in managing air temps without the extra current draw and wear of increased fan speeds.

 

i believe the stock one comes on at 108 and the fc is 95.


i currently have the waterpump, thermostat housing assembly off the vechicle and was going over anything that NEEDED replacing. I added the FC radiator assembly w/ tube, returned it to a stock waterpump pulley along with a fresh waterpump gasket, replaced many of the m6x1 bolts and gave it a several coats of high-temp enamel (primer, aluminum silver, and a clearcoat).

The sensor in it now is the stock "108" switch but I'm probably gonna wait on the switch this round and put the money towards chadwick's idler pulley setup that he's got.

 

if you are running A/C in the summertime the FC thermoswitch will be useful

 

I suppose if someone just wanted the higher fan speed, the thermoswitch relay could be jumped with the same signal that the ecu relays get, or the one for the a/c relay. It would just be a matter of cutting/removing the thermoswitch signal wire from the relay and running another signal line from either the ecu relay, ac relay, a toggle switch, a boost activated switch or even an adjustable temperature switch. There are many options available and it would be rather simple to implement.

 

Arghx, thanks for explaining why sometimes my fans stayed on after shutdown. I have the fc thermoswitch. It is very rare when the fans would stay on when i shut the car off but i thought that it was a relay sticking. so thanks again for clearing it up. I really need to just spend a day or two and read the service manual.

John

 

I have found in Atlanta summers that it makes a big difference for the fans to kick into high speed at 97C (or is it 95?) with the FC thermoswithc rather than 108C with the stock thermoswitch. Frankly, if my car ever gets much above 100-105C I start getting concerned. Also, with the FC thermoswitch, the fans will stay on after you turn the car off if you have been running above 97C. With the stock, you have to have been running above 108C for this to occur. So in summary, with the PFC and datalogit, you can program the fans to turn on (low speed) at whatever temperature you wish (I think I have it set at 89C), then the combination of A/C, load, and thermoswitch will control the middle and high speeds, but you reach high speed at 97C rather than at 108C if you have the FC thermoswitch.

 

Yes, that would make the fans always run at medium speed when the PFC triggers them--or however you wire it. But that doesn't help with the aftercool circuit unless you modify that as well.

A lot of people don't mind having a manual switch in their car, but a lot of people do. I sure don't want one. "normal" cars don't need that. After 5 years of Rx-7 ownership I got tired of driving a "weird" car that needs unusual shutdown rituals etc and can't be driven by other people without a 30 minute briefing. but it all comes down to personal preference I suppose.

I like the Rx-8 cooling fan control circuits. Every relay is controlled directly by PCM outputs, without an external thermoswitch or external A/C switch in the circuit. If you have the right software you can change the turn-on temps in the ECU based on vehicle speed etc. It also takes into account underhood temps using the engine compartment temperature sensor built into the underhood-mounted PCM.

 

I'm a bit **** about the car's under hood temps, before and after shutdown. I have my pfc fans set to come on at 85 C. I also have an FC thermoswitch. In addition to those, I have the "two minute delay" switch wired to the fan plug by the ECU.

When I come home, I always prop open the hood immediately after shutdown. I do this with the belief that all the rubber and plastic under the hood will have an extended life. I would recommend this to anyone that has a secure garage.

 

This question seems silly to me but the FSM doesn't give anyway to check the thermoswitch. In short, is there anyway to check the thermoswitch besides getting it to the operating temp?

 

You may be able to stick it in a pot of hot water and then check continuity from the terminal to the body

 

Yeah, that's the only way I was thinking of. I wish we had one of those dots on the sensor screen of the commander... That would have been brilliant!

 

It's in there. Page E-17. But you'll have to remove it.

 

I looked in the FSM, maybe somethings different in my 95 manual... I'll check it out when I get in the shop tomorrow!