cooling fan function related to ac high press switch

[chitowncelica]

Hello tech guys,

I ran into a technical diagnosing problem:

How does toyota integrate the water coolant temp sensor signal with the ac high press switch?

I am looking at the wiring schematics for a 92 celica and i had an over heating problem I talked to the celica forum a bit about.

But I am very confused as to how Toyotas send the signal from the coolant temp sensor to the ac high press switch and then to the fan relay.

What does the ac high press switch have to do with the fans function. I would think if anything, that signal wold be bounced to the relay for the ac cooling fan relay, not the engine radiator cooling relay.

Am I missing something?

I am a bit useful under the hood of most GMs and Fords, but my lack of exposure to Toyotas, makes me seem like a ignorant rookie when it comes to not so complex issues as engine cooling.

Anyway, as i told the Celica group, I replaced coolant sencor and relay and the fan fires up when hot and doesnt stop till I shut the car off. Now Im not sure if this is normal, but Im guessing it shouldnt overheat anymore.

Thanks again for listening and any info.
Take care guys, good job on the site
Tony

[thespud]

Tony:
I'm not too sure about the Celica's, but i know the corolla's have two cooling fans, one on the a/c side and one on the engine coolant side. The idea of this, is one primarily runs it's own 'radiator', but also helps to cool the other. The a/c cooling fan will come on when you turn the a/c on, because the more air flowing over that radiator, the better. Both fans will go on when hot, and should only die when turned to the accessory position as the engine is at operating temp and will overheat if they go off.

The fans will stay on afterwards (even in the Lock position), however, if the car has overheated, to help cool the engine back to operating temprature,then will switch off once there (I found this out when my engine cooked itself)

To get to the main point, the a/c switch really has nothing to do with the fan relay directly, it just puts more load on the engine and increases the idle thru the vacum valve, which in turn heats it up quicker. This then triggers the Coolant Temp sensor to turn the main cooling fan on, thus, both fans are then running.

Hope this answers your question at least a little.. If all is normal, including your thermostat and water pump, you shouldn't overheat again, no.

Spud.

[chitowncelica]

Thanks for replying and the info.

Same setup two cooling fans, one for ac, other for engine. I understand your post entirely. However i had one question, when you say:

"Both fans will go on when hot, and should only die when turned to the accessory position as the engine is at operating temp and will overheat if they go off."

So the fan will not go off once on, even if the engine were to cool down while the car is running? or does the engine not cool off enough at all once it reaches operating temp and the fan kicks in for it to go off? this is where im confused.

Ive got a tech2 for gms and a scanner, but no import cartridges, I dont even know if I can run diagnostic checks on the ecu to see if it gives me any feedback or at least tell me the engine temp so im not basing my work off the dash needle, which never goes past halfway.

Spud thanks for the info though, I appreciate you taking the time to reply to me. You take care and have a good one.

Tony

[thespud]

When idling, the car is set to run at operating temprature so it wont have to heat up again, reducing the problems that go with warming up, so the fans wont go off, because if they do, the engine wont correct itself and will overheat. Also, the coolant is at operating temp too.. If that is pumping thru an engine at operating temp without any air cooling it at all, it will boil over and you'll lose all of your coolant. Thus, the fans will never go off because the engine never cools down enough for the coolant temp sensor to let them.

[lcarocha]

Answered yesterday in the Celica forum, please don't double post.

Thanks