Help me understand how the blower control relay is wired

[Eicca]

Working with a situation where the fan speed knob for the A/C blower was bypassed to a very rudimentary on/off switch attached to the dash. This switch turns the fan on whether the key is in the ignition or not. I assume that the wires that usually run from the climate control panel were cut and rerouted to the switch. However, the fact that it turns on without the key in the ignition is a bit of a concern. Is the power supply to the blower control relay always hot? I'm not good enough at reading wiring diagrams to figure that out.

Question 2: I'm just looking for ideas of adding resistance to that switch to see if it is still connected properly to the relay. If adding resistance changes the fan speed, I should be able to just replace the climate control panel, wire the relay back in and be good to go. What impedance would I need to accomplish this? A guitar pot might do the trick if it has the right range. Is there some way to use a multimeter to add impedance?


I'm asking here in hope that the design of the 100-series and the Lexus GS400 are close enough that I can figure out how the system works and get a good idea of how to fix it. From all of the searching I've done it seems that they are (and the 1UZ layout is comfortingly familiar, might I add). I'm buying said GS tomorrow morning (it's immaculate with the exception of the switch issue described). I've been plowing through the Lexus forums but those are considerably less helpful than 'MUD when it comes to technical issues like this. It's all exhaust and coilovers in that place.

Plus, if our 100's climate control ever has issues, I'll be a qualified expert...

Thanks in advance.

 

[Mike6158]

The climate control system appears to be microprocessor based (see attached schematic).

My LC will occasionally "decide" to not turn the AC fan on. It happens infrequently. Usually when it's 105 outside and the LC has been sitting in the sun. It cools but the fan won't come on so I just open the rear vents and turn the AC to flow thru. Sometimes it's like that for 30 or 40 minutes. Sometimes it waits 3 or 4 minutes and turns on full blast. Idk if the controller is intermittent or there's a loose wire or connection. Or maybe a bad sensor.

 

[Trunk Monkey]

Test the wire with a volt meter, trace the wires to see if they wired to hot. Why not ask the PO why they did and and rewire it back to stock?

 

[Eicca]

The climate control system appears to be microprocessor based (see attached schematic).

My LC will occasionally "decide" to not turn the AC fan on. It happens infrequently. Usually when it's 105 outside and the LC has been sitting in the sun. It cools but the fan won't come on so I just open the rear vents and turn the AC to flow thru. Sometimes it's like that for 30 or 40 minutes. Sometimes it waits 3 or 4 minutes and turns on full blast. Idk if the controller is intermittent or there's a loose wire or connection. Or maybe a bad sensor.

Yeah sounds right. A multi-stage relay controlled by different input voltages makes the most sense.

Test the wire with a volt meter, trace the wires to see if they wired to hot. Why not ask the PO why they did and and rewire it back to stock?

Whoever did this is too far down the PO chain to contact.

Here's hoping it was just a quick clip-n-splice right at the relay.