AC cooling off the engine??

[cfg83]

ChampagneSW2 -

Originally Posted by ChampagneSW2

the refrigerant going to your A/C condenser is very hot..it goes straight from the compressor outlet to the condenser, so your theory of cool gas couldn't work.

They automatically turn the fan on when you hit the A/C button because that is the most efficient way to run the A/C. The more cooling you get in the condenser the more cooling you get in the car.

That is interesting that the guy was insulating his pipes...in any car I've seen the expansion valve in the A/C system was right in front of the evaporator in the car. But he does have an idea that you may get some heating of liquid refrigerant right before the expansion valve.

Welcome to EM!!!!!

Bingo. I tested this with blackjackel's 2005 Corolla and it does the same thing. I didn't intuit that it was more efficient. I thought the reason was to make sure that the additional A/C load didn't overheat the engine (i.e. if A/C on when it's hot outside, then turn on fan).

Turning on the A/C in Saturns is a(gain a non-intuitive) way to cool off the engine.

CarloSW2

[ChampagneSW2]

Thanks Carlo...nice car

well you're right it does serve the purpose of not overheating your car as well...so it serves two purposes of efficiency and preventing engine overheating.

[Xringer]

Originally Posted by ChampagneSW2

I can't say for certain this applies to every vehicle on the road, but every one i have owned turns on the condenser fan no matter what when the button is pressed. Literally, the fan is in the circuit for the A/C so there is no choice in the matter. When the button is pressed, condenser fan turns on. Most A/C diagnosis charts tell you to look at the fan when pressing the A/C button as that shows whether the circuit has power or not.

aerohead you are right at 55 mph it should get adequate airflow but there is no logic to prevent it from coming on based on speed, temp, etc.

Maybe some logic circuits need to be added in this case.?.

How about the AC fan only comes on IF the radiator temp is 200 deg (or more). Where main radiator fan voltage is already on..

Maybe the AC fan would never come on if you were zipping down the highway at a good clip.?.

My guess is. Better MPG!

Edit:
I just looked up the diagram. The relays for both fans are hardwired in parallel. They will always come on together. I wonder why they just didn't use one relay? Or maybe just a larger fan?

Maybe I could try a test switch to open the lines to those two motors
when I'm out on the highway.. And see how the AC would work without those two motors running.?.

[johnmyster]

At highway speeds your fans never turn on. Your thermostat opens up and coolant flows. Airflow is sufficient to cool the motor. Only if it continued to get hotter would the fans kick in - IE, stop and go where airflow is low.

The fans on your car run with the A/C, regardless of temperature. The extra airflow is cooling your motor to a lower point, until the thermostat cuts off cooling flow enough to maintain this new, lower temperature. You've observed a 5 degree swing. Seems about right.

You're seeing the swing because thermostats open over a RANGE. At 188 it only flows a little bit of water. However, it's enough to keep you cool with the fans running because the radiator is more efficient at rejecting heat with the fans going. Fans off, you're running at 193. The thermostat flows more water at 193, which helps your radiator to reject the heat with less airflow. Both are equillibrium cases.

Some cars have this "speed" logic. Later GMs do. The logic goes like this. Fan(s) run anytime the temperature gets above the set point(s). They also run if the A/C is activated. However with continuous speeds over 45 or 55 MPH, this A/C activation is disabled. Likely, your ECM is unaware of vehicle speed, and thus, this logic was not implemented on your generation of ECM/PCM/Body Control communications.

I'm installing electric fans on my truck and will have a manual switch allowing me to have fans with A/C around town, and to turn off that requirement on the highway. However, even with the fans decoupled from the A/C operation, they'd still kick on if the temperature got too hot. Worst case scenario, I notice the A/C isn't cold. Reach down, hit the switch, fans go. If you do put in a disable switch, be sure to do it in a manner such that the computer can still cut them on if things get too hot.

[johnmyster]

Originally Posted by Xringer

I just looked up the diagram. The relays for both fans are hardwired in parallel. They will always come on together. I wonder why they just didn't use one relay? Or maybe just a larger fan?

Two fans are better than one. In the case of failure, you've got another. Plus, radiators are usually wide and short rather than square. Two fans give better coverage in most cases. Two relays? Again, sometimes relays fail. Plus, they'll last way longer if they only switch the load of one fan rather than two.

[wagonman76]

Ive only got one fan and it comes on automatically with the AC. Except at over 70 mph. So says my service manual.

[Xringer]

70 mph!! Maybe I should have driven faster!!

Thanks for the comments guys. I learned a little more about my 'V'..