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Interesting observation, a/c on lowers coolant temp. #5437730 05/24/20 05:42 PM
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Jeff8820 Offline OP
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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?

Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437735 05/24/20 05:47 PM
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Turning on the AC also kicks on the cooling fan(s).


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Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437740 05/24/20 05:53 PM
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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./

Re: Interesting observation, a/c on lowers coolant temp. [Re: Char Baby] #5437743 05/24/20 05:54 PM
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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

Re: Interesting observation, a/c on lowers coolant temp. [Re: Char Baby] #5437763 05/24/20 06:14 PM
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Originally Posted by Char Baby
Turning on the AC also kicks on the cooling fan(s).

+1


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Re: Interesting observation, a/c on lowers coolant temp. [Re: Char Baby] #5437764 05/24/20 06:16 PM
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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.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437770 05/24/20 06:23 PM
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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!

Last edited by Jeff8820; 05/24/20 06:27 PM.
Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437780 05/24/20 06:27 PM
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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.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: ammolab] #5437787 05/24/20 06:33 PM
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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.

Last edited by Jeff8820; 05/24/20 06:40 PM.
Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437795 05/24/20 06:43 PM
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I also never realized how important those cooling fans were at idle, seeing real time temps, now I know.

Last edited by Jeff8820; 05/24/20 06:44 PM.
Re: Interesting observation, a/c on lowers coolant temp. [Re: Char Baby] #5437810 05/24/20 06:59 PM
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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.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: Char Baby] #5437819 05/24/20 07:10 PM
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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.


I thought it was to pull air through the condenser.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: dishdude] #5437844 05/24/20 07:28 PM
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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.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: dishdude] #5437855 05/24/20 07:34 PM
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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.


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Re: Interesting observation, a/c on lowers coolant temp. [Re: Jeff8820] #5437872 05/24/20 07:46 PM
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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.


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