Hi all,
I am working ona 96 SL for a friend of a friend. She told me it overheated on a longer drive but not on small local drives. Here is what I have done so far:

ETA: Fuse is good

Fan does not come on when the A/C is started. Recirc switch was not turned on.

Jumpered the fan directly to the battery. The fan works.

Temp gauge is working. I never drove the car, just let it warm up in the driveway. Temp gauge got to about the half way mark. No fan start up.

I switched the A/C relay and the cooling fan relay and both relays click when the A/C starts. Both relays are working.


The "service" light is on, but I didn't have my code reader to check it. I will do that later today or tomorrow, today if it heplps me get a solution to the problem.

Since the temp gauge is working do I assume the coolant temp sensor is good? Or is there a check I can do on it to see if it's working? I did do a continuity check but just got a momentary beep instead of a continuosy beep like I should have for continuity. I was using a Fluke VOM.

Ooorrrrr Do I just swap out the temp sensor and see if it changes anything?

Thanks for all the help!!
Scooter

 

<edited: follow OA's troubleshooting below>


Also -- fan will come on at 3/4 tick of temp gauge on S cars with a correctly functional ECTS (which drives both the temp reading to the PCM and the dash gauge). 3/4 tick this is entirely normal, though often harrowing for those working on an S car for the first time. Just remember the gauge is not linear.

Do not let this engine actually overheat, as the heads are prone to warpage in such situations and other fun things.

______
i would also consider a coolant flush and fill after a pressure test to be sure there are not other cooling system issues.

As for the Service light -- do you mean the Service Engine Soon or the Service light with the wrench?

 

The Service light with the wrench

 

OK -- look under the hood, and check the fan fuse, I suspect it is broken/blown.

As I read your message I realized that you swapped the A/C relay and the FAN relay, and both relays ran the A/C ok, but didn't run the cooling fan. The only way you got the cooling fan to run, was to directly wire to the fan motor. That means you are not getting voltage to the fan relay socket --> hence, a bad fuse.

 

Sorry!! Forgot to put that in the OP! The fuse is good. I will edit the OP to reflect this info

 

(sigh) -- ok

That leaves only one other possbility - a defective wire in the harness bringing the voltage to the fan, or a broken or missing ground wire

 

Good read, OA -- I missed that possibility

Scooter -- follow OA's troubleshooting

If the ECTS has never been changed I'll bet it has failed (the original design ECTS s pretty much all failed --design flaw) -- but address that AFTER you get the fan working

 

Derf --

I agree, that the ECTS might be bad, but if he switches the A/C on to max cool, the PCM will override the ECTS, and trigger the relay. Since we know the fan WILL RUN (from his previous tests), we need to find out if the relay will supply +12volts to the fan

 

Thanks Guys! Sorry about the lack of posting the part about the fuse being good
I was just going to post a question about which wire goes from the relay to the fan so I could check it for continuity, but this should tell me the answer to that. I wil update the post tomorrow.
Scooter

 

DUH --- my bad -- don't know where my head was, OA......

went back and modified my posts so others don't run down the wrong path

Sorry Scoot