How should the aircon fan and radiator fan work?

[dr. d]

from what i remember,
in cars that have their engines positioned laterally,
with the aircon off, the engine's thermostat will turn the radiator aux fan on or off, depending on engine temp.
with the aircon compressor running, the aux fans for radiator and for aircon will both run.

[runner10]

Yesterday i saw the "overheat" indicator light up in my 2015 Honda City's dashboard. So I immediately pulled over and checked under the hood. Upon my own observation, my radiator & reservoir had enough water. Radiator aux fan was working -- it turned on automatically when it reaches a certain temp. However, I noticed that when I turn on the AC, the aircon aux fan does not turn on. The aircon aux fan should turn on immediately when I turn on the AC, correct or does it only turn on when it reaches a certain temp? Anyway, it did not turn on at all even with the AC turned on for 10mins -- as such, i suspect this was the cause of the overheating.

Is this normal? Should the AC aux fan immediately turn on simultaneously with turning on the AC or does it have to hit a certain temperature before it turns on? Any idea how much to replace AC aux fan motor and the best place to have this replaced na hindi sa Casa???

Thanks in advance mga ka-City for your advise on my problem.

[oj88]

Based on my experience with Hondas, both fans should run at full speed whenever the A/C compressor is running, no matter what the engine temp is.

[dr. d]

with the aircon control set to maximum cool,
that aircon aux fan should rotate, regardless of what the radiator aux fan is doing.

bring it to the aircon shop.
the aux fans should be easy to troubleshoot.
bypassing the thermostat/relay should turn it on.

[shadow]

Based on my experience with Hondas, both fans should run at full speed whenever the A/C compressor is running, no matter what the engine temp is.

This sabay talaga dapat pag bukas ang a/c


Sent from my iPhone using Tapatalk

[oj88]

For something as critical as aux fans, they should already have a locked-rotor signal in this day and age. We take that for granted in PC CPU and case fans for well over 20 years. Cars with aux fans has been around much, much longer with the potential for engine damage much higher.

It can either report back to the ECU the RPM of the aux fans and compare it with acceptable values, OR at the least, detect if the fan rotor isn't turning when it should. So when the fan(s) don't achieve a certain speed or has stopped turning, it could trigger a DTC.

[dr. d]

For something as critical as aux fans, they should already have a locked-rotor signal in this day and age. We take that for granted in PC CPU and case fans for well over 20 years. Cars with aux fans has been around much, much longer with the potential for engine damage much higher.

It can either report back to the ECU the RPM of the aux fans and compare it with acceptable values, OR at the least, detect if the fan rotor isn't turning when it should.

my overheating sentra was one such. the problem had been going on for some months, and i couldn't see the problem.
it was solved when an old-timer mechanic showed me the way.
"umi-ikot naman, ah! malakas pa nga, oh. tignan nyo."
"boss, bili ka nang bagong aux fan, and i will show you just how strong it should be."
he was right.
by my estimate, my old fan was rotating at about half of what it should be. it would have passed muster, to the in-experienced like me.

another time,
i was losing coolant, and i couldn't see from where.
finally, i (or rather, my mekaniko) saw it.
it was a leaking 4 inch long black rubber hose, near the intake manifold. i didn't even know there was a hose there. i couldn't see it because of the jumble of electrical wiring above it.

[Miles_on]

The old 90's box type Sentra (SGX model ata?) of my classmate's dad had a weird quirk.
If you don't switch on the A/C, you'll see the thermostat rising until it hit the red & mag-o-overheat siya.
They demonstrated it to me several times when I'd hitch a ride with them. I don't think the fans switched on at all if the A/C is off.

Perhaps this was a design flaw of that model, or baka may sira lang talaga unit nila...

[dr. d]

The old 90's box type Sentra (SGX model ata?) of my classmate's dad had a weird quirk.
If you don't switch on the A/C, you'll see the thermostat rising until it hit the red & mag-o-overheat siya.
They demonstrated it to me several times when I'd hitch a ride with them. I don't think the fans switched on at all if the A/C is off.

Perhaps this was a design flaw of that model, or baka may sira lang talaga unit nila...

this might be similar to the old honda city that was discussed years ago.
that car's radiator aux fan was dead.
as a result, the engine would overheat.
but the driver noticed that the engine would get cooler if the aircon was turned on.
as it turned out, when the aircon was turned on, the aircon's aux fan turned on and cooled both the aircon heat exchanger and the radiator behind it.

i also had a minor issue with my 97 sentra.
when i had my aircon fixed in banawe, upon putting back together, speed 1 was higher than speed 2.
i complained that they probably put it back wrong. but they showed me that indeed, their connections were correct.
we got another control, and upon installation as per specified wiring connection, the result was the same: stronger 1 and weaker 2.
explanation???
"ibalik na lang nyo sa kung papano nyo unang nakita."
that did it. putting it back the 'wrong way' and it was back to normal. 1 weak, 2 stronger, and 3 strongest.
highs.

[yapoy86]

dun sa toyota altis, pag malamig pa then on AC, mag ON na din aux fan pero nasa speed 1 lang.. pag nasa operating temp na with AC, mag speed 2 na ang aux fan

eto sa mazda3 parang ganun din.. mas tahimik lang yung aux fan compared dun sa altis..