OldLs400

Today was a hot day. We had the a/c in the 98 ls400 running for about 4 hours straight. Toward the end, after starting the car up from a stop, the a/c fan didn't kick in as expected.

The fan eventually kicked in after 1 or 2 minutes and it worked fine.

Later, the fan stopped working again. We heard some clicking noises.

Where should I start looking? I'm going to check the fuses tomorrow when it's not as dark. What about the relays? Would it even be a fuse or relay, since it seems to at least work sometimes? That means it's getting power, right, so it shouldn't be a fuse or relay?

How hard is replacing the blower motor myself? I already have the glovebox out from messing with the ECU a while ago. Any sort of guide?

Thanks in advance. Love this place. Have learned how to replace vvti valves, brake pads, ecu, hood struts, etc. here.

Yamae

There is 1 more item you need to check. It is a blower motor controller used between the relay and the motor. It controls the motor speed using a method PWM. In order to distinguish, I'd observe the output waveform or the voltage of it at the terminal of the motor first.

I also need to inform you that the controller has a function to limit the excess current. This works when the motor's load is too much or the motor's winding is short-circuited.

OldLs400

Is the controller the same thing as the blower motor resistor I keep hearing about?

Yamae

The resistor is not the same with the controller but those two's functions are similar. The resistor reduces the current but at the same time it generates heat in accordance with the Ohm's law. On the other hand, a 98's controller almost don't because of the PWM. Semiconductors inside of the controller controls the current just turning ON and OFF the current very quickly. The ON/OFF ratio is given by the HVAC.

OldLs400

Thank you so much. Do you have a diagram of where this all is?

Yamae

I have a diagram but it is in Japanese language.

OldLs400

If you could post it that would be great. I just need to know where everything is and where the bolts are.

Anyway, I checked the 60A heater fuse in the engine bay today. It looked blown--there was a lot of brown plastic. I replaced it. The fan started working again.

However, I noticed a clicking coming from the AC. When I tried to cycle the A/C fan on and off, the fan refused to come back on.

I checked the relay again and it doesn't appear to be burnt.

I'm thinking maybe something in the motor is causing an obstruction and causing it to draw too much current and thereby blowing the A/C relay?

No matter what, I want to get the relay and resistor removed to check them out.

Your diagram, even in japanese, would be invaluable.

Yamae

You need to find out why the fuse is blown. The load of the heater fuse is only the motor via the controller. The AC is not getting any power from this fuse and the problem must be caused by the motor itself or the controller, you can assume from the diagram attached. According to a JDM diagram, the fuse for the blower motor is 50A as you can see at upper left corner. The motor and the controller can be found in the bottom. The signal name "SI" is coming from the HVAC to control the PWM ratio and change the fan speed.