Electrical question - coolant warning switch

[supraguy@aol]

Hey folks,
There is a temp switch installed in the thermostat assembly, which acts as an overtemp switch.
My understanding, is that once the coolant reaches a certain temp, it activates the a/c fans.
What i'd like to know, is which sensor is it on the T-stat assembly, and exactly what temperature it activates at.
Thank you in advance.

 

[jetjock]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=AC&P=33

Can also be used for an in cabin temp alarm.

 

[supraguy@aol]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=AC&P=33

Can also be used for an in cabin temp alarm.

EXACTLY why I needed to identify it. Thankyou for taking the time to look where I already should have.

 

[jetjock]

You be welcome. Note both switches are on the radiator side of the thermostat. On my car both activated the fans. You can simply pull off the connector and ground each (key on) to see what happens on yours. I say that because over model years there was some goofiness about how that AC fan stuff got wired.

I forget which switch I used for the alarm but I believe it was the 234*. It was whichever one turns the AC Amp off. I also rewired to allow the fans to run with the key off, a simple mod that can be done at the fan relay connector.

Btw on my car the fans would only come on 10-15 minutes after shutdown and even then only on hot days. High AC pressure aside its been my experience the fans should not operate while the engine is running. If they do it's a warning of problems in the cooling system.

During the years I worked on these cars this has been verified several times. If you notice the fans operating on a stock cooling system, for example at a stop light or when you've just arrived at your destination and haven't yet turned the key off, you'd better pay attention.

 

[supraguy@aol]

...I forget which switch I used for the alarm but I believe it was the 234*...


Btw on my car the fans would only come on 10-15 minutes after shutdown and even then only on hot days. High AC pressure aside its been my experience the fans should not operate while the engine is running. If they do it's a warning of problems in the cooling system.

I was planning to use the same one, as I would expect the transient temps could surpass 100c during the summer, perhaps after highway driving, for example.
I used to have Flex-a-lite's hooked through relays to an aftermarket temp switch with a ~105c switch point(which I still have at the bvsv location, but intend to remove), and it would cause both fans to come on for 10 minutes after shutdown because the engine's heat would continue to soak into the coolant. I found that if I wanted to be able to start my car later rather than get a jump start(those Flex-a-lite's draw alot of power), I would have to shut down, let the fans kick on for about 30 seconds to cool the contents of the rad, then start it and idle for 10 seconds to move it all into the block. Very tiresome.
I looked at my Tstat cover and the switches therein, and the lower one is clearly marked "100", but the one above is marked "73". Would you know if this is in fact the 112c switch?

Edit- I found online that part# TS73 is a temp switch "for gauge", so this is confusing me a bit more.

 

[Nick M]

I added a parallel ground to the A/C high side switch with a toggle. For very occasional track duty, and no other reason. All 3 of my electrics come on when I ground it through the toggle. It has to be before the swtich.

 

[supraguy@aol]

High pressure?
Are you referring to the switch mounted on the passenger frame rail? I think you are at least.
That's a good idea for track use for sure, but I just want to run a warning led in the dash, as well as a beeper.

 

[grimreaper]

Water temp switch# 2 controls the fans, closed at 234*F.
Water temp switch #3 must be the one to turn off the clutch relay. Closed at 212*F.

Cant find switch #3 on the online TWED though. Only control of the clutch relays is via the ac amplifier that I can see.

According to the tsrm, switch #2 is closer to the turbo/rear of engine on the water neck. #3 is closer to the radiator.

 

[jetjock]

He is. Excessive high side pressure also energizes the fans via the high pressure switch.

I don't remember which temp switch is which. You could pull one out and test it or pull off the neck to test. The other thing is to ohm out each switch to pin 11 at connector B1:

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=143

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=28

You're gonna have to get at B1 anyway to connect your devices unless you're willing to penetrate the firewall with a new wire.

Edit: All I can tell you is I connected to B1 pin 11 and never heard the alarm. I knew it was working because I tested it on occasion. If you get different results you can always connect to the higher switch. Or maybe my switches were backwards. Who knows. As I said there was some weirdness across model years about how all that was wired. Added fans, extra relays, that sort of stuff.

I wouldn't have thought fans, even high current ones, would run long enough to where you'd need a jump unless the battery is tired but since I had the stock fans current draw was less. Which reminds me: the car had a Priority Start unit on it, as do all my cars today. Another worthwhile addition that saved my butt several times even though they're installed primarily to protect the wife and kid.

 

[Nick M]

The dual pressure switch and the high side switch are both above the wheel well, tucked down low in the compartment. Go by the EWD if you do it. But it seems like the wire was white and the other blue with a tracer. And the white might have had the black tracer. But go by the EWD.

 

[Nick M]

Yeah, blue with white and white with black. And the plug on the switch is long and in a bundle.

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=144

 

[supraguy@aol]

Ironically, i just picked up an actual 1988 EWD manual from Ebay, and am going to start diving into it to find B1. And as you you mentioned, JJ, i am probably going to just test the suspect switch by heating it, as well as checking the wiring color. Thanks guys.

 

[jetjock]

Well, you made me go and dig up my old EWD where I recorded all the mods I did. The switch I used, the one that goes to the AC amp, is the top one on the neck. It's has a single white 1/4" faston type terminal. The lower switch has a round blue connector.

 

[supraguy@aol]

Sorry, didn't mean to 'make' you go do that, but glad you did.
Yeah, that's the switch i'm looking at, the one with the '73'' on it.

 

[jetjock]

No problem. It was bugging me. Funny thing is according to the EWD that switch shouldn't turn the fans on but in my car it did.