- Sat Feb 20, 2016 5:39 am
#6111
A/C low-side pressure is dependent upon the volume of Freon in the system, the temperature of the Freon leaving the evaporator and the efficiency of the condenser with regards to transferring heat from the Freon to atmosphere and thus influences the temperature of the Freon exiting the condenser. Not sure why that's so hard for some to understand since the ideal gas law explicitly allows for it. If that weren't true, one wouldn't be able to determine the mass of air entering an engine based on pressure and temperature, now, could they?
Your post saying that few vehicles use temp sensors in the radiator to control the fan... may I remind you 30 years of VW, Honda, Toyota, Chrysler, GM and others who do exactly that?
VW did so with the Rabbit/Golf, Polo and others such as the Dasher / Quantum / Passat and corresponding Audi vehicles.
Chrysler K chassis and similar derivatives like the Omni/Horizon, Reliant, Daytona and so on did that.
GM products like Camaro and Trans-Am, Corvette, Cavalier, Grand Prix and such did that.
Toyota Celica's, Tercel and others after the transition to FWD/AWD did that.
Honda did that starting with my motorcycle and most of the PGM-FI things that came from it.
-- Just checked and I can buy a fan switch for a 2010 Civic at my local AutoZone.
And I'd hazard the guess that most people looking to run Speeduino likely wouldn't be running it on any vehicle newer than 2000 or so.
So, to say it's not common is a HUGE stretch of the imagination, considering I just listed 5 of the top automakers in the world who have done it, and continue to do it, and have done so with most of their most popular vehicles.
With regards to your previous post and my replies to it, you convolute things much more than necessary without doing anything that otherwise counters my assertions.
Yes, running the fan based on the coolant exit temp being near the engine's safe, maximum temperature is probably a good thing, but when you've hit that point, nothing the radiator can do will cool you down, because if you did it my way, which unfortunately would either put fan control out of the ECU or otherwise burden the ECU with another sensor, the fan would've already been running if the radiator can't cut it based on ambient air flow alone.
I listed things that can cause the coolant temp leaving the engine to be above ideal, of which only a few bore any relation to the radiator and the need to run the fan. The radiator itself could be highly efficient, read as very oversized, and the temp of the coolant leaving the radiator could be equal to ambient air temp even without a fan running, which itself would be impressive, but... a highly loaded / stressed engine could raise the 70-100F coolant temp right back up to 210F or so when the coolant leaves the engine. Given that, does the fan need to run? No.
The logic behind that reasoning is self-explanatory.
To go back around to the A/C analogy....
The evaporator transfers heat from the air in the room to the Freon in the system, much like the cooling system transfers heat from the engine to the coolant. The Freon then travels over to the condenser, analogous to the radiator on a vehicle, where that heat is transferred to the atmosphere. The evaporator (engine) has no way of knowing the efficiency of the condenser (radiator) with regards to transferring heat to the atmosphere so using the temp of the Freon (coolant) exiting the evaporator (engine) isn't any indication of how efficient the condenser (radiator) is in removing heat from the Freon (coolant), and thus not relevant to when the condenser's (radiator) fan should run.
I think I mentioned previously that an automatic transmission could overheat an engine.
What's your take on that?
PSIG wrote:Keep going with the rest of it. The difference in your answer is that the AC is using the target requiring control (low-side pressure data) to control the fan, and you are translating it into something related but completely different—the outlet temperature of the condenser—and trying to make an analogy. The condenser outlet temperature is a factor in the low-side pressure change. That does not mean you want to control the fan using one of the factors, instead of the control target (low-side pressure). You can't use condenser outlet temperature as an example for fan control when the system you are describing does not use it either. No fair.No big difference.
David
A/C low-side pressure is dependent upon the volume of Freon in the system, the temperature of the Freon leaving the evaporator and the efficiency of the condenser with regards to transferring heat from the Freon to atmosphere and thus influences the temperature of the Freon exiting the condenser. Not sure why that's so hard for some to understand since the ideal gas law explicitly allows for it. If that weren't true, one wouldn't be able to determine the mass of air entering an engine based on pressure and temperature, now, could they?
Your post saying that few vehicles use temp sensors in the radiator to control the fan... may I remind you 30 years of VW, Honda, Toyota, Chrysler, GM and others who do exactly that?
VW did so with the Rabbit/Golf, Polo and others such as the Dasher / Quantum / Passat and corresponding Audi vehicles.
Chrysler K chassis and similar derivatives like the Omni/Horizon, Reliant, Daytona and so on did that.
GM products like Camaro and Trans-Am, Corvette, Cavalier, Grand Prix and such did that.
Toyota Celica's, Tercel and others after the transition to FWD/AWD did that.
Honda did that starting with my motorcycle and most of the PGM-FI things that came from it.
-- Just checked and I can buy a fan switch for a 2010 Civic at my local AutoZone.
And I'd hazard the guess that most people looking to run Speeduino likely wouldn't be running it on any vehicle newer than 2000 or so.
So, to say it's not common is a HUGE stretch of the imagination, considering I just listed 5 of the top automakers in the world who have done it, and continue to do it, and have done so with most of their most popular vehicles.
With regards to your previous post and my replies to it, you convolute things much more than necessary without doing anything that otherwise counters my assertions.
Yes, running the fan based on the coolant exit temp being near the engine's safe, maximum temperature is probably a good thing, but when you've hit that point, nothing the radiator can do will cool you down, because if you did it my way, which unfortunately would either put fan control out of the ECU or otherwise burden the ECU with another sensor, the fan would've already been running if the radiator can't cut it based on ambient air flow alone.
I listed things that can cause the coolant temp leaving the engine to be above ideal, of which only a few bore any relation to the radiator and the need to run the fan. The radiator itself could be highly efficient, read as very oversized, and the temp of the coolant leaving the radiator could be equal to ambient air temp even without a fan running, which itself would be impressive, but... a highly loaded / stressed engine could raise the 70-100F coolant temp right back up to 210F or so when the coolant leaves the engine. Given that, does the fan need to run? No.
The logic behind that reasoning is self-explanatory.
To go back around to the A/C analogy....
The evaporator transfers heat from the air in the room to the Freon in the system, much like the cooling system transfers heat from the engine to the coolant. The Freon then travels over to the condenser, analogous to the radiator on a vehicle, where that heat is transferred to the atmosphere. The evaporator (engine) has no way of knowing the efficiency of the condenser (radiator) with regards to transferring heat to the atmosphere so using the temp of the Freon (coolant) exiting the evaporator (engine) isn't any indication of how efficient the condenser (radiator) is in removing heat from the Freon (coolant), and thus not relevant to when the condenser's (radiator) fan should run.
I think I mentioned previously that an automatic transmission could overheat an engine.
What's your take on that?