v1xiii Posted August 16, 2009 Report Share Posted August 16, 2009 Ever since I bought my '88 quest, for some reason the ventilation fans will not shut off. Every button on the climate control responds correctly when pressed, and in fact the off button even beeps, but will not shut off the fans. Any ideas where to start the gremlin hunt? Link to comment Share on other sites More sharing options...
Tim_C. Posted August 16, 2009 Report Share Posted August 16, 2009 I have not owned an '88, but whatever the temperature is set to, the system will try its best to achieve it with the fans. If it is set to a hotter temp than what is in the car currently, it will open the water valve to the heater core and warm it up. If a colder temp is displayed, it will close the water valve, and run the vents even with the AC off. My '85 always runs the fan to keep the temp at the setting. The only way I have found to turn it off is to pull the fuse. Link to comment Share on other sites More sharing options...
mikec Posted August 16, 2009 Report Share Posted August 16, 2009 On 88s, and 87s for that matter (and probably 89s) if you select OFF the fan motor is OFF, period. Pressing AUTO will let the a/c computer control the fan but when you press OFF, you've taken the fan away from the computer. The computer will continue to adjust the air vent actuators, the heater, etc, trying to get to whatever temp you've dialed on the display. Which I find annoying - when I select OFF I want the whole stinkin' system OFF! It's really annoying to select OFF and then 20 minutes later find my feet are roasting because the stupid computer thinks it needs to let the heater run, with "ram air" flow, to raise the interior temp 2 stupid degrees. Pressing the ECON button twice actually disables the computer to put the system in total manual mode. The computer controls the fan via 2 methods: 1: a Darlington Pair power transistor which is mounted to the fan case actually - so fan air will cool it. The computer uses this transistor to vary the fan speed between 10 speeds in a/c mode, 8 speeds in heater mode, and 2 speeds in manual mode using the two fan buttons on the control panel. 2: a relay that bypasses the darlington transistor for maximum fan speed. If either of those items is shorted out, the fan will run full speed at all times. How to tell which is your bug? Remove the panel underneath the glove box (two screws, then it pulls towards the rear of the car - there is a sensor taped to this, don't pull it apart) and you'll see the big black plastic box with the evaporator (part of the a/c) inside it... and a couple small modules screwed to the side of it. Two of those modules will be relays. One will have black, blue+black, black+yellow, and a red wire. Unplug that relay and start the engine. If the fan speed now responds to the dash buttons, either the relay is bad or the a/c computer piece that controls this relay is shot. With the relay removed, the fan speed should have the 10 steps in AUTO mode at least. If the fan motor still runs full speed... turn off the engine and put the relay back in. Look around the fan motor (black cylinder hanging from the white plastic box on far end of passenger footwell) for a small black module attached to the bottom of the white plastic... follow its wires to a connector. Unfortunately that same connector is the motor connector so we can't just unplug it and test... you'll have to unplug the connector and then manually re-connect the black and blue+red wires to the motor wires they mate to. (those wire colors can be anything by the way) mike c. Link to comment Share on other sites More sharing options...
v1xiii Posted August 16, 2009 Author Report Share Posted August 16, 2009 awesome info, I'll see what I can find out Link to comment Share on other sites More sharing options...
v1xiii Posted August 17, 2009 Author Report Share Posted August 17, 2009 (edited) Ok, so I finally got that relay connector you described disconnected and the fan still ran as fast as ever. I'd like to try checking this second connector you described, but I'm not sure I follow you there. I disconnect the connector and manually re-connect the black and blue+red wires to the motor wires they mate to. What should this cause or inform me of when I do it? Edited August 17, 2009 by v1xiii Link to comment Share on other sites More sharing options...
mikec Posted August 18, 2009 Report Share Posted August 18, 2009 Ok, so I finally got that relay connector you described disconnected and the fan still ran as fast as ever. I'd like to try checking this second connector you described, but I'm not sure I follow you there. I disconnect the connector and manually re-connect the black and blue+red wires to the motor wires they mate to. What should this cause or inform me of when I do it? The second connector is both the Darlington transistor and the motor. With just the motor wires jumpered/connected, you've taken the darlington out of the circuit. Try running the fan - it should be dead at all times until you press the high-speed button on the panel; that'll kick in the relay which should run the fan. (this is the relay you unplugged in the first test - it's gotta be plugged back in now). If the motor is OFF most of the time, and only works on high speed with the relay, then the darlington is shorted out and must be replaced. The darlington is screwed to the fan housing near the motor; it's just a odd looking thing. I doubt you'll be able to buy a new one these days though used ought to be easy from folks parting cars. Usually these things are quite durable so buying a used one is not too risky. If the motor still runs full speed all the time... your car has goofed-up wiring. You'll probably have to take the insulation tape off the wiring harness and follow it back looking for a hack-job. mike c. Link to comment Share on other sites More sharing options...
v1xiii Posted August 18, 2009 Author Report Share Posted August 18, 2009 Ok, I follow you now. Thanks, I'll check it out. Link to comment Share on other sites More sharing options...
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