...noticed my LS400 starting to overheat and saw that the driver side condenser fan wasn't turning on.

I did unplug the temp sensor fan at the bottom left of the radiator. Pass fan turns on with ignition, nada from driver side.

Is it motor or relay? I know there's a few electrical things to troubleshoot but would like to follow a procedure if one has been made.

Did a search but couldn't find anything for just one side.

 

the relays need to be checked. They're mounted behind the drivers headlight. They're a relay for each fan if I'm not mistaken. I would start there.

 

that is the one for the coolant fan switch i think. unplug the switch and turn the ignition on..the fan should spin. if it doesnt then maybe check the switch or run 12 volts directly to the fan to make sure its still good..the passenger side is the ac fan. also im not sure they both come on at the same time..ever. i could be wrong about that

 

Really? They're both not supposed to come on when the AC is on?? I could have sworn both did. Can someone check? I have a 92 btw. Thanks to both of you for your info.

 

I just fixed a problem with the cooling fans on my 91 LS, so I'm familiar with the wiring setup. I have attached it for your reference. The cooling fans are dual speed and should both be spinning at the same time whenever they are running.

There are two switches that control the fan operation. One is the water temp switch at the bottom of the radiator and the other is the a/c high pressure switch which is located behind the passenger side headlight. Both switches are normally closed, thereby providing ground to cooling fan relay #1 and cooling fan relay #2, which causes each relay (which are n.c.) to open. If the water temp rises beyond a certain temp, the water temp switch opens (which is equivalent to when you removed the connector at the bottom of the radiator) and causes both fans to spin at high speed (the two fans are in parallel and each receiving ~13 volts). Whenever the a/c is running, and assuming the a/c head pressure is within normal range and your a/c high pressure switch is working normally, then both fans should be running in low speed (the 2 fans are in series and each receiving ~6.5 volts). In other words, both fans are normally running on low speed whenever the a/c is on.

The cooling fan relays are located behind the driver's headlight. I would start by testing the relays as per the manual. They are easy to test. If you want to try a quick test, try swapping your relay # 1 and relay # 2 and see if the driver's fan motor works. If it does, then you have found a bad relay. You can also easily test the driver's fan motor by connecting it directly to the battery with some suitable jumper wires (use at least 12 gauge). You should connect an ammeter in series if you do this to confirm that the motor current is between 4.2 and 4.4 A.

 

91LS400vgb, thank you for your post. It helped a lot. I did remove the two connectors. I didn't use an ohmmeter but what I did was use a test light. Both fans are getting power. So I swapped the relays as you mentioned and drivers side was still out. So I wired it directly to 12v and it still didn't turn on. So I guess we can chalk it up to being the drivers side fan motor.
Interesting enough the wire color for the pairs are different. While positive and negative are on the same side, the colors of the wires change. Drivers side is white/blue pair with blue being positive. Passenger side is white/blue with white being positive.

Going to buy a working fan motor at Pick A Part tomorrow.

Also my blower in the cabin doesn't blow fast like my friends LS400. I saw on a schematic that there is a high speed blower fan relay. Any ideas on how to test if that's working.

 

nice post 91 ls400vgb.

 

Nice job isolating the problem.
Below is the logic of how the blower motor operates. You'll have to confirm with a test light and a multi-meter that it's doing what it should. The relay itself can be tested by confirming that 4 & 5 are normally open and that 4 & 5 show continuity when voltage is applied to 1 & 3. I hope this helps.

 

91LS400vgb, thanks man you have been a lifesaver. I really recommend you come up with your own AC Bible thread for UCF10/11 models. I'm sure it will come in handy with the links to help others.

Thanks to others who responded as well.