In a nutshell: I'm planning on using the A/C circuit in the 3FE ecu to increase idle speed for other purposes and I'm interested if anyone sees any problems with the following plan.
Background: I'm running a 175 amp alternator (Mechman) with a pulley that's been turned undersized to increase the alternator speed at idle (with dual batteries, 1/0 cables and with the batteries grounded directly to the alt). Despite these efforts depending on load I get between 12.3 and 13 volts at 650 rpm idle. At 900 rpm I get 14.4 volts regardless of load. Currently this is only a little annoying as my headlight output jumps around a bit while crawling in traffic. However I'm in the process of converting to a Lincoln Mark VIII electric fan and I want to crank up the idle rpms to increase the alternator's output when either the headlights or the fan are on (this should also help idle cooling as the waterpump will spin a bit faster).
The plan: This looks simple to do - the A/C "amplifier" runs current to the magnetic clutch on the A/C compressor when it needs to run. This line has a splice to the A/C circuit in the ecu. When the clutch is on the ecu sees battery voltage between the A/C and ground pins. I'm planning on tapping this line and supplying battery voltage to the A/C pin whenever the fan or the headlights are on. I'm going to use a diode in the original line to make sure that voltage from the headlight/fan splice doesn't feed back to the A/C amplifier or the magnetic clutch in the compressor.
Any thoughts on this?
Thanks,
Joel
Background: I'm running a 175 amp alternator (Mechman) with a pulley that's been turned undersized to increase the alternator speed at idle (with dual batteries, 1/0 cables and with the batteries grounded directly to the alt). Despite these efforts depending on load I get between 12.3 and 13 volts at 650 rpm idle. At 900 rpm I get 14.4 volts regardless of load. Currently this is only a little annoying as my headlight output jumps around a bit while crawling in traffic. However I'm in the process of converting to a Lincoln Mark VIII electric fan and I want to crank up the idle rpms to increase the alternator's output when either the headlights or the fan are on (this should also help idle cooling as the waterpump will spin a bit faster).
The plan: This looks simple to do - the A/C "amplifier" runs current to the magnetic clutch on the A/C compressor when it needs to run. This line has a splice to the A/C circuit in the ecu. When the clutch is on the ecu sees battery voltage between the A/C and ground pins. I'm planning on tapping this line and supplying battery voltage to the A/C pin whenever the fan or the headlights are on. I'm going to use a diode in the original line to make sure that voltage from the headlight/fan splice doesn't feed back to the A/C amplifier or the magnetic clutch in the compressor.
Any thoughts on this?
Thanks,
Joel