Cooling fan question
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The fan controls are more complex than just switching the fan on when the AC compressor runs. Many vehicles with a mechanical cooling fan also have an auxiliary electric fan for times when engine and vehicle speed do not provide enough air flow. I've owned 2 of those, a 2001 Dakota 4.7 with tow package and a 1997 BMW M3.
I know on my VW, word was that if the fan(s) did not come on, then the ac would not work. I found out that it worked happily with only one working fan (other froze up / died). It seemed fine on hot summer days too, so I'm not sure just how much it monitor fan operation.
My Tundra has but just one fan, the mechanical one.
My Tundra has but just one fan, the mechanical one.
One system turns one fan on when the AC is engaged and the other when a radiator mounted thermostat sees a high temp. Others run both fans in series (half voltage each) when the AC is engaged and switches to parallel (12 volts) when the temp rises enough. There are mechanical fans with a clutch controlled by the AC circuit which engages when the AC is turned but can also be engaged by a thermostat when the AC is off. Then there are the mechanical fans with a fluid coupling, as the fluid is heated it gets thicker and drives the fan faster as the air from the radiator warms up. Volvo used fluid drive fans for years. Toyota for a few years in the 90s used fans driven by oil pressure provided by the power steering pump. Apparently they couldn't get electric fan motors at the time powerful enough to drive the fans without killing the alternator.
They also use a switch that turns off the compressor if high side pressures go over 425 psi.
JHZR2
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Originally Posted By: Joshua_Skinner
The fan controls are more complex than just switching the fan on when the AC compressor runs. Many vehicles with a mechanical cooling fan also have an auxiliary electric fan for times when engine and vehicle speed do not provide enough air flow. I've owned 2 of those, a 2001 Dakota 4.7 with tow package and a 1997 BMW M3.
+1. Even my 1981 MB 240D is set up this way.
The fan controls are more complex than just switching the fan on when the AC compressor runs. Many vehicles with a mechanical cooling fan also have an auxiliary electric fan for times when engine and vehicle speed do not provide enough air flow. I've owned 2 of those, a 2001 Dakota 4.7 with tow package and a 1997 BMW M3.
+1. Even my 1981 MB 240D is set up this way.
Originally Posted By: Joshua_Skinner
The fan controls are more complex than just switching the fan on when the AC compressor runs. Many vehicles with a mechanical cooling fan also have an auxiliary electric fan for times when engine and vehicle speed do not provide enough air flow. I've owned 2 of those, a 2001 Dakota 4.7 with tow package and a 1997 BMW M3.
Yep my jeep is set up the same.
4.7 V8 and IMHO it needs both.
The fan controls are more complex than just switching the fan on when the AC compressor runs. Many vehicles with a mechanical cooling fan also have an auxiliary electric fan for times when engine and vehicle speed do not provide enough air flow. I've owned 2 of those, a 2001 Dakota 4.7 with tow package and a 1997 BMW M3.
Yep my jeep is set up the same.
4.7 V8 and IMHO it needs both.
I have my low speed fan disabled on my Genesis Coupe due to tuning issues. For some reason it was on all the time. There is just the one electric fan and the ECU controls the high speed for high AC pressure. I have a mechanical temperature switch to turn the high speed fan on when the coolant hits 200F or so.
But the AC works with no fan until the pressure is too high. I have two LED lights connected to the fan relay coil and the AC clutch coil ground that come on when the relay is activated. You can watch as the AC compressor runs then drops out due to high pressure and the high speed fan comes on. When the pressure drops the high speed fan turns off and the AC clutch is then reactivated.
Bottom line is the high pressure switch is what determines the need for air flow over the condenser. On the 90's era Tauruses I had it was the high pressure switch that turned on the fans and turned off the compressor coil.
But the AC works with no fan until the pressure is too high. I have two LED lights connected to the fan relay coil and the AC clutch coil ground that come on when the relay is activated. You can watch as the AC compressor runs then drops out due to high pressure and the high speed fan comes on. When the pressure drops the high speed fan turns off and the AC clutch is then reactivated.
Bottom line is the high pressure switch is what determines the need for air flow over the condenser. On the 90's era Tauruses I had it was the high pressure switch that turned on the fans and turned off the compressor coil.
To answer your question, yes, a mechanical fan pulls enough air through the A/C condenser for that system to work properly. Some have auxiliary electric fans, and some don't. Your Tundra is set up just like my first car, an '84 Cutlass. One large mechanical fan with a viscous fluid clutch. Even when it's "freewheeling", it's pulling a lot of air across that condenser and radiator.
Our 14 RAM has a viscous clutch driven fan running off the engine and a small electric unit as a booster when needed. I have met RAM owners who did not even know the lil electric was even there.
My sig car has two hugely powerful electric fans. They have two speeds and are triggered to low speed almost all the time as the AC is on constantly here. High speed is triggered by coolant temp, transmission fluid temp and AC high side pressures (demand).
My sig car has two hugely powerful electric fans. They have two speeds and are triggered to low speed almost all the time as the AC is on constantly here. High speed is triggered by coolant temp, transmission fluid temp and AC high side pressures (demand).
Depends on the vehicle. Cherokees with A/C up to 1999 would cycle the electric fan with the A/C compressor *or* when the engine hit a certain temperature. My 2000, and 2001 Cherokees won't turn on the electric fan until the engine hits 220. Difference in programming but one doesn't rely on the other - I've lost the electric fan and had no issue with the A/C running.
My focus turns on the fan when I hit the AC button and seems to run it constantly.
My focus turns on the fan when I hit the AC button and seems to run it constantly.
Originally Posted By: supton
On setups with a mechanical fan, do they just assume adequate airflow from the freewheeling fan?
No assumption needed; with a normal application (Chevy gas truck with A/C), you're looking at 20%-30% shaft speed when disengaged, and 80%-90% when engaged. As Hokiefyd pointed out, "even when it's "freewheeling", it's pulling a lot of air across that condenser and radiator", and he's exactly right.
On setups with a mechanical fan, do they just assume adequate airflow from the freewheeling fan?
No assumption needed; with a normal application (Chevy gas truck with A/C), you're looking at 20%-30% shaft speed when disengaged, and 80%-90% when engaged. As Hokiefyd pointed out, "even when it's "freewheeling", it's pulling a lot of air across that condenser and radiator", and he's exactly right.
I can confirm on late model ('05.5-'10) VW Jetta's that the a/c does still work if either of the fans die. I had one of the two fans die on my '06 Jetta and it most definitely impacted the A/C performance when stopped in traffic but the a/c kept chugging along.
The remaining operational fan was running at full tilt pretty much constantly which is what made me realize there was an issue as it was rare previously to have it ever hit the 3rd stage (highest speed). You could hear that sucker in the car with the windows up and standing in front it sounded like the other fan was trying to pull the car around.
The remaining operational fan was running at full tilt pretty much constantly which is what made me realize there was an issue as it was rare previously to have it ever hit the 3rd stage (highest speed). You could hear that sucker in the car with the windows up and standing in front it sounded like the other fan was trying to pull the car around.
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