L31MaxExpress
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I am reserving this thread for a writeup on the PWM controlled Trailblazer electronic fan clutch swap. I will be adding information on how to wire it and control it in the near future. The P59 controls a solid state relay that sends a PWM signal to the clutch. The clutch has a RPM feedback signal to the PCM. The PCM has limits set for the RPM of the fan as well as has the ability to soften the fan engagement at WOT if the coolant temperature is under a specified value.
If you need a clutch fan on your hard working truck it is an interesting way to make the fan clutch act in a repeatable, consistent manner. I added a 3 wire ac pressure transducer to my van years ago when I had electric fans. The PCM refrences both coolant temperature and ac pressure to provide a programmed PWM output to the clutch, controlling the fan rpm thus lowering noise and power consumption when the fan is not needed as much.
At WOT the PWM signal is reduced to a minimum (IIRC it is about 15% on) if the engine and transmission are at normal operating temperature, avoiding the massive power loss of a fully engaged clutch fan in hot weather. The PCM has a paramter to set for the pulley ratio of the fan drive. On my van it is 33% underdriven and the fan turns 66% of the crank rpm if the clutch were fully locked. At 6,000 rpm (fuel kill) the fan has a maximum RPM potential of 3,960 rpm if the clutch were seized. I have it programmed to run 3,200 rpm max and I have it programmed for 350 rpm minimum. I find the fan rarely needs more than about 30-40% of full engagement which means the fan rarely turns more than 2,000 rpm.
Prior to wiring up and enabling the PWM control and RPM feedback loop, I had a 16" electric fan mounted to the back of the radiator in front of the clutch fan inside the shroud. The P59 triggered the electric fan on Fan1 output. Fan2 output triggered a simple relay and fed power to the control circuit on the fan clutch. The electric clutch thus had 2 modes, a slower freewheeling mode similar to a non-engaged thermal clutch fan and a fully engaged mode. The PWM clutch is quick to fully engage, but slower to return to a freewheel state when it is controlled by a simple OFF/ON method. In the Clutch Freewheel / Fan 1 Electric / Fan 2 Clutch Engaged progressive engagement method the engine and ac were able to operate well on all but the most grueling days without the clutch fan fully engaging.
That being said even that arrangement had its benifit of less frequent fan engagement, less power lost, better ac cooling immediately after startup with a heat soaked interior, etc. Where the condenser heat is not enough to engage a standard clutch when the ac is struggling to cool a 140F cabin, the PCM controlled clutch will engage and pull air over the condenser due to the elevated ac head pressure.
I will post part numbers, a wiring diagram, fan settings from the P59, and a couple of pictures when I slow down long enough to gather them all in one place.
Here is the setup fully functioning this evening when I was topping off the ac. I had the idle locked at 1,500 rpm using HP Tuners Scanner program. It was 109°F ambient, engine was holding ~200°F and the ac was cooling 36°F out of the vents up front and about 40°F out of the rear vents after I added refrigerant to the system with the fan holding about 30% duty cycle. With the engine compartment heat soaked it rose to about 44°F out of the vents at normal idle speed and the coolant creeped up toward 210°F and the fan engagement rose to about 45% duty cycle. At that point both the ac vent temps and coolant temps stabilized and maintained those readings.
If you need a clutch fan on your hard working truck it is an interesting way to make the fan clutch act in a repeatable, consistent manner. I added a 3 wire ac pressure transducer to my van years ago when I had electric fans. The PCM refrences both coolant temperature and ac pressure to provide a programmed PWM output to the clutch, controlling the fan rpm thus lowering noise and power consumption when the fan is not needed as much.
At WOT the PWM signal is reduced to a minimum (IIRC it is about 15% on) if the engine and transmission are at normal operating temperature, avoiding the massive power loss of a fully engaged clutch fan in hot weather. The PCM has a paramter to set for the pulley ratio of the fan drive. On my van it is 33% underdriven and the fan turns 66% of the crank rpm if the clutch were fully locked. At 6,000 rpm (fuel kill) the fan has a maximum RPM potential of 3,960 rpm if the clutch were seized. I have it programmed to run 3,200 rpm max and I have it programmed for 350 rpm minimum. I find the fan rarely needs more than about 30-40% of full engagement which means the fan rarely turns more than 2,000 rpm.
Prior to wiring up and enabling the PWM control and RPM feedback loop, I had a 16" electric fan mounted to the back of the radiator in front of the clutch fan inside the shroud. The P59 triggered the electric fan on Fan1 output. Fan2 output triggered a simple relay and fed power to the control circuit on the fan clutch. The electric clutch thus had 2 modes, a slower freewheeling mode similar to a non-engaged thermal clutch fan and a fully engaged mode. The PWM clutch is quick to fully engage, but slower to return to a freewheel state when it is controlled by a simple OFF/ON method. In the Clutch Freewheel / Fan 1 Electric / Fan 2 Clutch Engaged progressive engagement method the engine and ac were able to operate well on all but the most grueling days without the clutch fan fully engaging.
That being said even that arrangement had its benifit of less frequent fan engagement, less power lost, better ac cooling immediately after startup with a heat soaked interior, etc. Where the condenser heat is not enough to engage a standard clutch when the ac is struggling to cool a 140F cabin, the PCM controlled clutch will engage and pull air over the condenser due to the elevated ac head pressure.
I will post part numbers, a wiring diagram, fan settings from the P59, and a couple of pictures when I slow down long enough to gather them all in one place.
Here is the setup fully functioning this evening when I was topping off the ac. I had the idle locked at 1,500 rpm using HP Tuners Scanner program. It was 109°F ambient, engine was holding ~200°F and the ac was cooling 36°F out of the vents up front and about 40°F out of the rear vents after I added refrigerant to the system with the fan holding about 30% duty cycle. With the engine compartment heat soaked it rose to about 44°F out of the vents at normal idle speed and the coolant creeped up toward 210°F and the fan engagement rose to about 45% duty cycle. At that point both the ac vent temps and coolant temps stabilized and maintained those readings.
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