So the a/c will only kick the fan on if there is pressure in the ac lines? What causes the low speed fan to kick on? What temp does the water temp sensor tell the fan to kick on? Any info on this at all will be greatly appreciated. I have a schematic and the wires are all good rang them out yesterday and I put a jumper in the relay and the fan is good I have let the car sit and idle all the way up to about 210 and the fan never kicked on.
Ok, low speed fan operation:
Low speed fan is controlled by a) ECM according to coolent temp via the sensor in front of the intake, pointing forward, with the black and yellow wires. Fan on temp is a parameter set in the chip. b) low speed fan is also commanded on by the AC high pressure switch. I am not sure what pressure closes the low speed contacts. There will be two green wires leading to the low pressure fan relay. If you ground either of them, the low fans should come on. If not, inspect for 12v at the red wire to the relay. This wire comes from a fuse link located at the starter solenoid. If you have 12v, and grouding the green wire causes the relay to click, check the resistor at the cooling fan. Sometimes they crack causing low fan to become inop. If the relay doesnt click, check for 12v on the brown wire, which is keyed power, coming from the "PWR BRK" and/or "RLY" fuse under the dash.
high speed operation:
High speed fan is controlled by a) the temperature switch in the intake manifold pointing UP. It has a green/yellow wire to it. This switch closes at around 225-230* and will energize the high speed relay. b) the AC high pressure switch HIGH fan contacts, which close at approx 225psi. The high speed relay will obviously override the low speed one as the high bypasses the resistor built on the fans. This relay too gets its high current power feed from a fuse link at the starter solenoid, and the relay coil gets power from the same brown wire as above. The green/yellow wire is grounded by the high pressure switch and/or the coolant temp switch.
Any time the high fan is triggered, via the dark green/yellow wire, the delay relays counter is reset and if the delay relay loses power to the red wires, the timer begins to count down approx 10 minutes. While counting down the delay relay closes its contacts and power remains on the blk/pnk wire to the fans. The delay relays high current power feed also comes from the fuse links at the starter.
So, if the low speed fan doesnt work, ground the green wire. If the fans come on, then the PCM or the AC high pressure switch arent grounding the wire. If the fans dont come on, but the relay clicks, check for power on the red wire to the relay, if you have power on the red wire, check for power on the red/blk *WITH THE RELAY ENERGIZED*. If the fans dont come on and the relay doesnt click, check for power on the brown wire (key on, engine off)
Same holds true for diagnosing the high speed fan, but its the green/yellow you want to ground. The red and brown wires are common to both relays, so provided there isnt a problem in a harness, if you have what you need on one, you should have it on both. Oh, and the relays output wire TO the fan is a blk/pnk wire.
If the high fan works, but the low wont, and the relay switches 12v to the blk/red going to the fan, then check the fan speed resistor for power in and out.
Its really a simple system, not like the newer cars where they use each motor to drop current to change speeds and they use relays for on, off, high, low for each fan. THEY can be a pain. This should get you rolling. Let me know how you make out.
