I was wondering if its possible to simulate/bypass the refrigerant pressure switch. I'm pulling the A/C system on my LD9 (didn't work anyway) and i was thinking that i could use the A/C button on the HVAC as a cooing fan override button. I'm sure the rad fan runs whenever the A/C is engaged. I think if i can trick the PCM into thinking the A/C is running when i push the button i will also be able to control the fan. I've been looking at some wiring diagrams and it looks like the switch is a 3 wire potentiometer setup. I tried just jumpering 2 of the wires and can get the fan to start but can't shut it off without turning the ignition off. Does anyone know the resistance thats needed between these wires to make it work?
Edited 1 time(s). Last edited Monday, June 23, 2008 9:51 PM
Any one have any ideas???
You are speaking about the push button correct? What about turning the switch to A/C (vent/defrost switch). I have never done it with no A/C in the car.
FU Tuning
hmm never thought of trying that... runs out to car to try...
nope.. no go... i gotta figure out what the pcm needs in order for it to think the AC is running
You said the push button is a 3 wire set-up? Do you know what each of those wires are, or do? Meaning power, ground, signal? I'm thinking what would be easier to do, is use the button to ground the fan relay (which will turn the fan on). If you can push the button (it grounds relay), and then push it again (ground is taking away). I bet one of the wires off the button goes to the relay for the A/C (and grounds it), which flips the relay sending the signal to the compressor to come on. Find out which wire does that and move it o the same spot on the fan relay and you should be golden.
FU Tuning
John Higgins wrote:You said the push button is a 3 wire set-up? Do you know what each of those wires are, or do? Meaning power, ground, signal? I'm thinking what would be easier to do, is use the button to ground the fan relay (which will turn the fan on). If you can push the button (it grounds relay), and then push it again (ground is taking away). I bet one of the wires off the button goes to the relay for the A/C (and grounds it), which flips the relay sending the signal to the compressor to come on. Find out which wire does that and move it o the same spot on the fan relay and you should be golden.
No its the A/C refrigerant pressure switch thats a 3 wire setup. I haven't pulled the HVAC apart to see how the A/C button is setup. According to the wiring diagram in my Haynes manual everything is controlled by the PCM. The push button goes to the pcm and all the other stuff (pressure switch, relay control, etc.) goes there too. I'm thinking that i can use the push button to do just like you said but it'll involve running a wire from the push button to the fan relay.
The pressure switch is actually a pressure sensor. You can wire in a 1K pot to fake a pressure signal.
BLK = GND
Red/BLK = Signal Return to PCM
Gry = 5V supply.
When you short the 5V to the Signal line or ground the Signal line, that sets a fault (AC press sensor out of range) and the fan defaults on for the duration of the key cycle.
Hope your AC system is defeated while you experiment.
Mike
