91 s2 cooling fans cycle

[944s2c]

Hello, I have a 944s2 that has an interesting cooling fan problem.The fans run@high for about 5 seconds and then change to low for about 3 seconds.Removing the plug from the temp sensor and jumping pins 1&3 produces continuous hi speed oper ation . Jumping pins 1&2 produces hi for 8 seconds,lo for 3 seconds. I believe I have a relay issue.Can anyone shed some light on this?Thanks,Dan

[PorscheG96]

By jumping pins 1 and 2 you're grounding the low speed fan operation. In order for the fans to run at low speed they require two ceramic resistors to cut down on the voltage received by the fan motors. If you look under the plastic shroud at the back of your engine compartment [near the windshield wiper] you will see 2 ceramic pucks screwed to the firewall. One of those pucks will probably have leads that are corroded. You can try to brush the corrosion off or replace the faulty resistor. Your high speed fan operation [jumping pins 1 and 3] works fine because it doesn't require the resistors. When your fans run at low speed you need 2 resistors to reduce the voltage...if you only have 1 resistor working because the 2nd one is corroded the ceramic overheats and cannot reduce the voltage enough...if you touch one what is working double-time you will burn yourself. When you hear your fans cycling between high and low speeds the resistor is heating up and cooling down repeatedly.

[Z-man]

I had this problem with my 944S2 twice. Once, it was a corroded contact point on the fan switch. The other time, it was a loose or broken wire going into the fan relays. Took the mechanics a lot of hours to fix, but they figured it out both times. Give the guys at Powertech in Rockaway, NJ a call - perhaps they can steer you in the right direction (973-586-3210 website: www.pwr-tech.com ) tell them Zoltan sent ya!

Note: there was a Q&A question regarding this in PANO a year or two ago - their response was that the car was operating normally.

[Carroll Laird]

Your fan relay is operating as it should - it is sensing a high resistance or open condition in one (or both) of the low speed fan circuits and gives 7 sec. bursts of high speed operation for cooling. The relay will eventually wear out its contacts from doing this - this is a "limp home" mode. You need to correct the problem in the low speed circuit which is most often the resistors as mentioned above. Other problems in the low speed circuits like Z-man describes are of course also possible and a bit more "interesting" to find and fix.

Hope this helps...

[bazar01]

The radiator fans have two circuits as Carroll had mentioned. The short cycling is due to a failed low speed circuit and the fans are defaulting to high speed.

Check your wires to the fan resistors, they could be fried and open due to high amperage draw or age. If wires and connectors are fine, it's possible the fan resistors are open.

On an S2 hard top, the resistors are located in the passenger side firewall in the engine compartment close to the battery, just below the windshield. You have to lift up the plastic cover to get to it.

Hope this helps.

[944s2c]

Thanks so much for the info everyone!Iwill check it out and let you know what I find!Thanks, Dan

[944s2c]

Is the location the same in a cab??I have a '90 s2 cab.

[bazar01]

I think the resistors are located in a different spot in a cab. Look for an aluminum heatsink about 5" x 3". This is where the two fan resistors are mounted. The resistor is round ceramic type with a mounting hole in the center. They have to be in a cool ventilated area for better heat dessipation or under the passenger side footwell above the glove box.

[944s2c]

I found the resistors under the plastic cover as was described.The lower wire connection on the inboard resistor was heavily corroded.The insulation was also burned about 1 inch down the wire.I cleaned the connections and repaired the wire , then put dielectric grease on all the connections to prevent any further problems.I want to thank everybody for your input.You guys really saved me alot of time!Thanks! Dan

[bazar01]

Glad you fixed you fan issues. Good job!

[wjk_glynn]

Originally posted by Z-man
Note: there was a Q&A question regarding this in PANO a year or two ago - their response was that the car was operating normally.

I submitted that question to the PCA tech section and as you mentioned, the written response in Pano was that the car was operating normally.

However, Bill Buris of the PCA did a followup on their online version and corrected what was printed. Here's the corrected version online:

http://www.pca.org/tech/tech_qa_question.asp?id={F49B658F-B006-4D76-BD60-5566FB114E62}

I tried the solution, and it worked...

Karl.

[aggerz]

Hi,

I just thought i would add to this for information to help anyone struggling to find these resistors.

Please note this info relates only to '90 944S2, Cabriolet , Right hand drive.

I found them located up under the driver footwell towards the back on the fender side. it is a real mongrel of a spot to get at but if you persist and are flexible, you can get the 2 nuts off to remove the assembly. Getting it back on is fun also.

Hope that helps anyone with a RHD Cab from doing the searching i did

aggerz.