Interesting observation, a/c on lowers coolant temp.

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May 1, 2020
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Location
North Carolina
My 2001 Camry 4cyl has always had ice cold a/c, and still does. I recently downloaded a ECM Bluetooth app
that shows coolant temp , I was under the assumption that at idle running the a/c also raised the coolant temp, but I'm observing the opposite. it's 90 degrees F outside and if I let the car idle with no a/c it gets up to about 208 and the cooling fan kick on and the coolant temp drops a few degrees within one minute. If I turn the a/c on, it's stays right at 195-196 degrees indefinitely.
This is all at idle in a fully warmed up car.
Just out of curiosity I tried a couple different apps and they are all within 1 degree variance. I googled "coolant temp drops with a/c on" and all I see is the opposite, people with overheating with the a/c on.
Also the a/c stays ice cold at idle, it always has. The best a/c I've ever had. Thoughts?
 
Now I don't feel so bad about letting my car idle so much with the a/c on which I've done for years in this car, I always assumed the actual coolant temp raised about 10-15 degrees but apparently it's the opposite./
 
YUP! learned that trick when my coolent temp sensor died and my fans never came on. Caused my 97 Misubishi eclipse to overheat inline at the bank. Called the dealership (I was young back them) and they said just turn on the AC and drive on in. I thought they are crazy and argued with them that I wasn't the one overheating the engine was. " AC doesnt cool the ENGINE you idiot!!! "

Welp..... ate those words. turns out AC does cool the engine.
smile.gif
 
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.
 
I just didn't expect the a/c being on to actually lower the coolant temp, incidentally at the same outside temp at 75mph with the a/c on or off the coolant temp. pretty much goes to 195 and stays there. My wife's 2016 Explorer at idle very noticably starts losing a/c coolness until you start moving 30mph+, somehow this old Toyota keeps it chilled no matter. I wasn't planning on keeping the Camry this long but one of the main reasons is the a/c, I don't know how Toyota made the a/c so efficient , but it worked!
 
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AC does turn on the cooling fans...but so does rising temp in the cooling system. If your temp sensors, switches and relays are working you should never need to turn on AC to lower coolant temp.
 
Without the a/c on at idle the fan fans? come on at 208 degrees according the Bluetooth dongle, very quiet though you have to listen hear it click on. If I'm sitting at idle in 90 degree weather with the a/c cranked and the coolant temp won't go above 196 degrees I don't think my engine is having any trouble staying well within it's engineered temp. If anything this car has a tendency to run cool, years ago the thermostat stuck open and in 50 degree weather you couldn't get any heat and the temp actually dropped going anything above 40mph. Incidentally the beck/arnley thermostat I put in it was a piece of junk, replaced it with aisin brand one and that fixed it.
 
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I also never realized how important those cooling fans were at idle, seeing real time temps, now I know.
 
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Originally Posted by Char Baby
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.



Good point CB....

With my scan tool I have seen the same phenomena as the op... So now it makes sense to me.
 
Originally Posted by Char Baby
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.


I thought it was to pull air through the condenser.
 
Originally Posted by dishdude
Originally Posted by Char Baby
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.


I thought it was to pull air through the condenser.

It is.
 
Originally Posted by dishdude
Originally Posted by Char Baby
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.


I thought it was to pull air through the condenser.


It is. The load from AC on a modern engine is relatively insignificant.
 
Need to pull air through the hot condenser at idle (no airflow otherwise) to condense the hot refrigerant vapor into a liquid, so it can evaporate again in the evaporator & make it cold.
 
As others have stated, the fan coming on with the A/C has to do with moving air over the condenser only, and nothing to do with engine temp.

The coolant temp tends to remain steadier with the extra airflow through the radiator, balancing against the thermostat set point. Without the fans on, the temp is allowed to float up to some set point temps where the fan turns on.
 
Originally Posted by MNgopher
As others have stated, the fan coming on with the A/C has to do with moving air over the condenser only, and nothing to do with engine temp.

The coolant temp tends to remain steadier with the extra airflow through the radiator, balancing against the thermostat set point. Without the fans on, the temp is allowed to float up to some set point temps where the fan turns on.



Agree, but I wanted to add that this is normal and expected behavior for most vehicles with electric cooling fans. If your a/c condenser and engine radiator are inline with eat other in a sandwich configuration, you can witness this behavior with the hood open. Let the car idle without a/c, and within moments of turning on the a/c the electric fan will come on. N/A for vehicles with mechanical fans.
 
The engine will run relatively hotter (i.e. more heat is produced) with more load (a/c compresor) no matter how small the load is. it all depends on where you are reading the temperature.
with the a.c. on and the fan(s) on (taking heat away from the condenser), the coolant temp will look more regulated because the fan will also cool off the water. Without a/c, the fan(s) will turn on & off to cool off the coolant while thermostat is doing it's thing ... You will see more temp swing due to thermostat opening and closing and fan on/off ...
Also ECU is not sending instantaneous temp readings to odb port and it has a filter.
 
Originally Posted by ammolab
AC does turn on the cooling fans...but so does rising temp in the cooling system. If your temp sensors, switches and relays are working you should never need to turn on AC to lower coolant temp.


Exactly!
However, the fans turn on more often during city. stop & go type driving/idling with not as much air coming into the radiator, than it does while driving on the highway where there is lots of air entering into the radiator(no fans needed).
 
Originally Posted by Jarlaxle
Originally Posted by dishdude
Originally Posted by Char Baby
Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).


Because running the AC puts more stress on the engine which is why the fans turn on.


I thought it was to pull air through the condenser.

It is.


You're right, this too...I missed that. Duhhhh on my part!
smirk.gif

I mean, it all happens simultaneously that, I didn't think about that. Still, my bad!
 
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