Greetings. Just purchased a 1996 LS400 that looks to be in great shape. Failed Virginia State Inspection for a high pressure power steering hose leak and the defrost fan not blowing enough. Hose I can replace soon enough but the fan has me stumped at the moment.

The blower motor runs on low only when the automatic climate system is turned on. I believe that points me to the blower motor resistor. Does anyone have the pin diagram and resistance values I should be showing with the multimeter?

Thank you in advance.

 

I understand you want to check it as you mentioned. But unfortunately your idea is not quite effective because it's not a resistor but semiconductors. We call it a blower motor controller. It gets the control voltage from the A/C computer and changes the fan speed. Lower the voltage, faster the speed. Try grounding the pin #1 of it cutting the line from the A/C computer for the confirmation. Does the motor run in full speed? If it runs fast enough, apply that pin DC 3V. Is the speed reduced but still blowing rather strong? The DC 3V can be prepared using 2 dry batteries.

Another item I'd better inform you is that the A/C computer is sending the correct voltage to the blower motor controller or not. This can be manually checked observing the voltage changing 8.4V to almost 0V when you change the fan speed MIN to MAX.

 

Hope this helps:
https://www.clublexus.com/forums/ls-...r-problem.html

Looks like your vehicle doesnt have a BM resistor.
Blower speed is controlled by a BM controller.
Located right next to the blower motor. (2 connector, 3 wire and a 2 wire)
Im guessing the 2 wire goes to the BM to control the input speed. (power/ground)
The other 3 wires im guessing as well -- power and ground, one might be the from the display control switch to select blower speed.

 

Blower motor controller it is! All I was thinking of was cost of throwing parts at the problem. Weeks went by and I had decision paralysis. Local Import shop to the rescue. Controller good, resistor good, fan good. The dealer installed cellular phone was the culprit. The vehicle decided that a call was coming in from the defunk phone and reduced the fan speed to low so the call could come through without a lot of noise. Import garage disconnected a ground wire in the system and full functionality is back.

 

Thanks for coming back and sharing that!