1998 LS400
190K miles

i noticed yesterday that my front A/C fan was not on. My A/C works great. IS this supposed to come on anytime the a/c is running or does a certain criteria need to be met for these to turn on ? if it is supposed to be on anytime my a/c is running what could be wrong? do i assume the fan is bad or are there some relays that need to be checked? i found a few with similar issues on pre 98 cars. but didnt see anything for 98-00 models.

my coolant temps measured with an OBD scan tool show temps varying between 195-204 degrees sitting in stop and go traffic on my commute (16 miles).

thanks

 

There are certain criteria that must be met before the fan turns on, more than just AC on. I have seen mine on and off while AC is on. I am not sure what exactly needs to happen to trigger the fan but if I had to guess it would probably include both coolant temperature and AC high side pressure.

 

i had the same issue with mine. I have a 99. My car was overheating at idle with AC on, i noticed the AC fan wasn't turning on.

The problem is the relays under the drivers side headlight.

They aren't necessarily bad, but there was some nasty *** grease all over the relay contacts. I cleaned them up a little, and the fan kicked on.

I believe one of those relays is for fan low speed and one is for fan high speed.

Take out your drivers side headlight and you'll find the relays.

 

thank you. i will remove headlight and try to clean up the relays and see if that helps.

 

Here is what i found after removing headlight. What exactly should i be cleaning up. The grease ? Thanks for your help.

 

cleaned up the grease from the relays using a qtip. plugged them back in but the fan never kicked on.

not sure what my next step should be. Do i assume that the relays are bad or could it be a bad fan ?

its 80 degrees outside this morning and my temp using an OBD tool is showing between 192 and 196 degrees. Is this temp to high ?

thanks for any help.

 

relays could be bad possibly ?
The next thing that could be the issue is the thermoswitch on the bottom of the radiator.
I think the likelihood that the fan is bad is pretty small ,but always a possibility .

You should give power directly to the fan and see if it works

 

two relays would run about $18 from rockauto. so thats not too bad

is any coolant lost when replacing the thermoswitch at the bottom of the radiator ?

how would i give power directly to the fan to check that it works ?

thanks so much for your input Scraape

 

any way for me to test the relays prior to ordering new ones ?

 

that grease is actually there to promote conductivity. It prevents moisture and corrosion from getting in between the contacts. If anything I would buy a dollar packet of dielectric grease and relube those contacts.

Have you spun the fan motor to make sure it spins freely? make sure the motor itself isn't locked up before doing the work of removing all the relays.

 

This stuff,used by OEM car manufacturers.Whenever I take apart a connector on my vehicles I clean them with de-oxit,plug and unplug connector several times,then pack with DS-ES.Makes for some well protected connectors.
=================
https://www.lubriplate.com/Online-St...5-oz-tube.html
LUBRIPLATE DS-ES Lubricant is developed specifically for the electrical and electronics industry. LUBRIPLATE DS-ES Lubricant is being used extensively in automotive switches and contact units where performance is exceeding all of the new safety standards set for this equipment.

 

yes the fan does spin freely.

 

i replaced both relays under the drivers headlight. The fan still does not turn on. I ordered a replacement temp sensor which mounts under the radiator. Should my next step be to replace the temp sensor ?

 

yeah i would replace that sensor just in case. That didn't end up being my problem, but i replaced it for peace of mind.

If your fan still is not working then I would still try to give it power directly and see if it turns on then. Take it to a mechanic and they should be able to test it for you.

Turns out my car is still overheating at idle with the A/C on ONLY. But my A/C fan is definitely working when the A/C is on.

Next I might consider replacing my fan clutch. I'm thinking the overheating is either due to that or a A/C compressor that is about to seize up.

 

My fan is working. I happened to be replacing my front parking light bulb yesterday afternoon and i noticed it kicked on. So apparently the relays fixed the issue. With the front fan running i noticed the operating temps did not get above 190 degrees. Without it running it would get up to about 200 degrees in 85-90 degree outside temps. Thank You to all who provided input.