Thermo fans not running

[ls400]

Hi,

I have a '92 LS400 and the thermo fans are not running when the A/C is switched on. I beleive they should come on as soon as the A/C is switched on. The consequence of this is that the Aircon compressor is now locked.

Before the same thing happens with the replacement compressor, can someone give me some hints on troubleshooting the fan problem? I have already checked the obvious fuses for the fans, but would appreciate knowing what to look for next.

Thanks and regards,
Phil

 

[uza70]

check the hydraulic system for leaks, and check theres is fluid in it.


Use a multimeter to see if the voltage changes across the solenoid when the air-con is switched on.

If that fails, then find the cooling fan ecu (somewhere in the dash) and check its got connection to the climate control. And while your at it, check its got an earth and power.
Also that it is connected to the temperature sensor in the radiator, and that the sensor is working.

Basically, if the mechanics of the system look fine, start following wires.

 

[ls400]

Thanks for the comprehensive answer! I have a suspicion that it will be something in the dash, as the last time it was repaired, the aircon mechanic pulled the dash apart and replaced the evaporator. There were a couple of unrelated things not working properly after he re-assembled it (memory position and steering wheel tilt), so he may have rushed it to get it out of his shop. I didn't check at the time whether the fans were coming on with the air, I just assumed that all would have been done right. Grrr!

Anyway, thanks again...I'll see what I can find.

Regards,
Phil

 

[sideshow]

does yr ls400 have thermos or hydraulic fan setup
thought most were hydraulic

 

[ls400]

Actually, it has both! Twin thermo fans at the front of the radiator, hydraulic fan at the rear. In theory, I think the thermo's are for low speed operation, but in practice I think they are on all the time the aircon is. I never really took any notice until I had this problem.

Regards,
Phil

 

[sideshow]

the fans may be used for when the a/c system over pressurises
and they come on

i do know the hydraulic fan should speed up when u turn the air on
as the fan ecu monitors signals for when the a/c clutch is on and a/c pressure
gets hi or low not sure

 

[gloverman]

In most a/c systems there is a pressure valve lockout for the fans. If the a/c compressor is not working the fans won't work. Chances are the fans aren' working due to the pump not working. Cheers

 

[sideshow]

i could prob look at it but since ls400 are a big pain in the butt to work on
id want atleast 200 bucks an hour hhehehehehe

i would just take it back to last person who touched it maybe

 

[ls400]

In most a/c systems there is a pressure valve lockout for the fans. If the a/c compressor is not working the fans won't work. Chances are the fans aren' working due to the pump not working. Cheers

I wish I had've taken more notice now what the fans were doing back when it was working. It seems like a bit of a chicken/egg thing. I bought a remanufactured compressor from eBay US, and part of the sellers blurb included this; "Always check Condenser Cooling Fans both Clutch Driven by the Accessory Drive and or Electric Fans with Relays. This is the #1 cause of Compressor & Clutch failure! These Vehicles are Prone to Compressor Clutch Failure." I think I'll wait until it's replaced and gassed up before I go any further with troubleshooting.

i could prob look at it but since ls400 are a big pain in the butt to work on
id want atleast 200 bucks an hour hhehehehehe

i would just take it back to last person who touched it maybe

No, no, they're a delight to work on! How much for cash?

The problem with taking it back to the last guy was that it was literally years ago now. I lived without the air working for the last two summers, but now I'm using it more, I want to get it fixed. So, too late for warranty claims, and I'd be getting a guy to fix my car that I no longer trust. It pisses me off, but I'll just have to grin and bear it.

My plan is to install the compressor myself, then take it to an aircon mecahanic mate to do the re-gassing with the old r-12 gas. I'll troubleshoot the fan problem at that time, loaded with the info. you guys have given me!
:laughing:

 

[sideshow]

I think the cOmpressor might have been on way out also
As jap cars are getting old these days
Basically the hydro fan runs all the time
As temp goes up or air con is turned on fan goes to full speed
The elect fans should turn on when the pressure switch tells it
Not sure if it's when pressure is too hi or too low
I'd have to get my books out
But I do know if there is a problem behind the dash I doubt
I like to be one to pull it aPart Heheheeheheh
But find the workshop manual and read up on what turns
Fans on if your worried just bypass the fan triggers so they come
On when cOmpressor turns on

 

[sideshow]

Good luck getting old gas back in it

 

[uza70]

yeah the good ol' hardwire method for fans. it is an easy way to fix and ignore the problem.

 

[Peewee]

LS400's don't run a hydro fan, instead they have a viscous coupling fan (like the UZS131 Crown) and a pair of thermo's.

As others have stated, the thermo's are normally hooked up to an over-pressure switch in the aircon circuit. When you turn the aircon on (whilst there is no airflow), the pressure will rise and the fans should come on. Generally this will take about 10-20 seconds on a hot day.

When you go get it gassed they can fill the system up with nitrogen to this over pressure point and test the fans. Make sure they do this.

Also FYI, R12 is illegal to use (AFAIK), but there are a couple of drop in replacements that don't require any other mods. Not all places use these replacements though.
R134A (the current 'standard') requires about $30 worth of mods (fittings) to the current system before it can be gassed.