Paradigm Shift: Run A/C to keep your engine cool!
#11
09-11-2009, 08:49 PM
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Re: Paradigm Shift: Run A/C to keep your engine cool!
If the car was severely hot, then I would hope the electric fans would be on "high" speed already, so the A/C would not be needed as a trigger to get the fans on "high".
One thing I am quite positive of is, the A/C does NOT go off if the car is at WOT. I've confirmed this in my 2005 at least.
It would be only the compressor clutch that would go "off" with WOT. You may not even notice that since the blower would not be affected and there is generally some reserve liquid refrigerant in the system to make cooling available for a few minutes. Even if no refrigerant is available the evaporator operates at or near 34F so it might take a few minutes to notice that no cooling air is flowing.
*exception
*If A/C is on to the cabin, WOT will not turn it off. If however, A/C is on just for the battery pack ( in the 75-95'F range ) then WOT will turn off the A/C.
You think it would be the reverse, but nope. You would think the battery would have priority over the humans, but nope. Or it was a program error only for 2005, so I'd be curious to hear from owners of later models.
One thing I am quite positive of is, the A/C does NOT go off if the car is at WOT. I've confirmed this in my 2005 at least.
It would be only the compressor clutch that would go "off" with WOT. You may not even notice that since the blower would not be affected and there is generally some reserve liquid refrigerant in the system to make cooling available for a few minutes. Even if no refrigerant is available the evaporator operates at or near 34F so it might take a few minutes to notice that no cooling air is flowing.
*exception
*If A/C is on to the cabin, WOT will not turn it off. If however, A/C is on just for the battery pack ( in the 75-95'F range ) then WOT will turn off the A/C.
You think it would be the reverse, but nope. You would think the battery would have priority over the humans, but nope. Or it was a program error only for 2005, so I'd be curious to hear from owners of later models.
#12
09-11-2009, 09:00 PM
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Re: Paradigm Shift: Run A/C to keep your engine cool!
Having watched this one for a few days I have some thoughts.
Given that increased air flow through the radiator produced by running an electric fan or two will produce a lower coolant temperature, there are some errors in the thinking.
1st - The idea that an electric fan, of the same flow capability as a belt driven one, doesn't use as much or more engine power than a belt driven fan is wrong. It has to use more engine power because of the additional energy conversions involved and the power comes from the engine.
An interesting side bar: If the electric fan(S) were of the brush/commuator type it may act as a "genset" if the airflow form forward speed is high enough. Same might be true of a brushless but more design thought would be involved.
2nd - Some how the laws of thermodynamics seem to be repealed in at least one FEH. If the A/C is producing any cooling at all it will raise the engine coolant temperature proportionately because the A/C condenser is first and its output air is the input air to the engine radiator.
"Some", but not proportionately.
And no laws have been repealed. If the engine coolant temperature rises the thermostat opens more, more flow through the radiator makes up for the hotter radiator cooling airflow.
So if the A/C is running the engine is producing more power so its internal temps are higher. Thermodynamics is like that.
I believe that the only basis for the temps reported is the fact that the fans come on increasing air flow. Not a bad trick to have in your bag of tricks... but keep in mind that in most cases you are increasing engine power to do that.
The real issue is where is the thermostat set? The thermostat is set to produce efficient combustion by regulating the coolant temperature to a desired point.
Given that increased air flow through the radiator produced by running an electric fan or two will produce a lower coolant temperature, there are some errors in the thinking.
1st - The idea that an electric fan, of the same flow capability as a belt driven one, doesn't use as much or more engine power than a belt driven fan is wrong. It has to use more engine power because of the additional energy conversions involved and the power comes from the engine.
An interesting side bar: If the electric fan(S) were of the brush/commuator type it may act as a "genset" if the airflow form forward speed is high enough. Same might be true of a brushless but more design thought would be involved.
2nd - Some how the laws of thermodynamics seem to be repealed in at least one FEH. If the A/C is producing any cooling at all it will raise the engine coolant temperature proportionately because the A/C condenser is first and its output air is the input air to the engine radiator.
"Some", but not proportionately.
And no laws have been repealed. If the engine coolant temperature rises the thermostat opens more, more flow through the radiator makes up for the hotter radiator cooling airflow.
So if the A/C is running the engine is producing more power so its internal temps are higher. Thermodynamics is like that.
I believe that the only basis for the temps reported is the fact that the fans come on increasing air flow. Not a bad trick to have in your bag of tricks... but keep in mind that in most cases you are increasing engine power to do that.
The real issue is where is the thermostat set? The thermostat is set to produce efficient combustion by regulating the coolant temperature to a desired point.
#13
09-12-2009, 02:20 PM
Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: Paradigm Shift: Run A/C to keep your engine cool!
BTW... whenever in the past, and whenever in the future I refer to the A/C going on and off, I ALWAYS refer to the A/C compressor clutch being on, powered, engaged, doing work, otherwise spinning and compressing.
Duh...
I never refer to the climate control system, aka "blower(s)" that ovbiously run based solely upun switch condtion, and not engine condition.
I have a LED lamp that lights whenever the A/C compressor is working, plus it's state can be monitored with a ScanGauge as well.
FWIW, I also monitor the evaporator temperature via scan gauge, and generally the compressor goes off at 43-44 degrees, and comes on at 47-48 degrees. I don't think I've ever seen a reading in the 30's.
However, I do not know the exact point where the temperature is taken... but this is the temperature reported over the CAN bus. If the temperature probe is located 18 inches downstream ( wild guess, no basis, just for example ) from the evaporator, then the inferred temperature of the freon could be 34 degrees. We all know the car uses more inferred values than actual measurements. Your distance traveled for example is inferrred from how many revolutions pass of the transaxle. The water temperature is inferred from the cylinder head temperature. Your miles to empty is inferred from.... oh geez.... better not go there......
Duh...
I never refer to the climate control system, aka "blower(s)" that ovbiously run based solely upun switch condtion, and not engine condition.
I have a LED lamp that lights whenever the A/C compressor is working, plus it's state can be monitored with a ScanGauge as well.
FWIW, I also monitor the evaporator temperature via scan gauge, and generally the compressor goes off at 43-44 degrees, and comes on at 47-48 degrees. I don't think I've ever seen a reading in the 30's.
However, I do not know the exact point where the temperature is taken... but this is the temperature reported over the CAN bus. If the temperature probe is located 18 inches downstream ( wild guess, no basis, just for example ) from the evaporator, then the inferred temperature of the freon could be 34 degrees. We all know the car uses more inferred values than actual measurements. Your distance traveled for example is inferrred from how many revolutions pass of the transaxle. The water temperature is inferred from the cylinder head temperature. Your miles to empty is inferred from.... oh geez.... better not go there......
#14
09-12-2009, 09:43 PM
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Re: Paradigm Shift: Run A/C to keep your engine cool!
Most compressors cycle on and off as a function of refrigerant liquid pressure. Combination pressure switch also prevents the compressor from cycling at all if high side pressure is so low that refrigerant charge is low.
#15
09-15-2009, 02:12 PM
Re: Paradigm Shift: Run A/C to keep your engine cool!
I haven't set up my SG to read the A/C clutch, but when the weather is extremely hot (above 100F), and I am driving without the A/C button lit with a green light, I cannot believe that the A/C is not cooling the battery. This makes me wonder if the A/C does not always kick in the green light on the dash...
#16
09-15-2009, 02:27 PM
Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: Paradigm Shift: Run A/C to keep your engine cool!
My car did not come with any LED.
I had to install my own, directly wired to the A/C compressor clutch.
It's a DIY modification. Sorry I wasn't clear on that.
I had to install my own, directly wired to the A/C compressor clutch.
It's a DIY modification. Sorry I wasn't clear on that.
#17
09-15-2009, 06:26 PM
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Re: Paradigm Shift: Run A/C to keep your engine cool!
That bright flash of the LED as the power to the clutch is switched off the result of inductive "kick" from the clutch windings. You may want to add a "squelching" diode to the circuit to prevent premature failure of the LED. Didn't need that with the DIY I did years ago with an incandescent bulb.
Post #15 "begs" a question of you, do you see the clutch being activated to cool the battery with the cabin A/C off..??
Post #15 "begs" a question of you, do you see the clutch being activated to cool the battery with the cabin A/C off..??
Last edited by wwest; 09-15-2009 at 06:30 PM.
#18
09-16-2009, 08:43 AM
Re: Paradigm Shift: Run A/C to keep your engine cool!
Ah, that makes sense. Why didn't you just program your SG to read the clutch?
#19
09-16-2009, 02:26 PM
Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: Paradigm Shift: Run A/C to keep your engine cool!
I did it long before I had the New SGII.
I did it so I could tell when the A/C was running for the pack, when the cabin A/C was off, way before I had battery temp monitoring and more with the SGII.
I did it so I could tell when the A/C was running for the pack, when the cabin A/C was off, way before I had battery temp monitoring and more with the SGII.
#20
09-24-2009, 08:56 AM
Re: Paradigm Shift: Run A/C to keep your engine cool!
The initial post was designed to lure people into thinking that,
with electric fans and such, they could use less power & run at
lower power output.
Go back & look at what you wrote.
with electric fans and such, they could use less power & run at
lower power output.
Go back & look at what you wrote.
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