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Carroll Laird's Avatar
 
Join Date: Nov 2001
Location: New Orleans, LA
Posts: 85
Cooling Fans 101

Just came through a stretch of unusually hot DRY weather during which I noticed the engine temp in traffic was staying between the two middle bars after the fans kicked in (at about the upper middle bar, not the red one). Normally it would go back down to just below the first middle bar and the fans would turn off. Under the hood, it was obvious. Only the driver side fan was working. I had recently changed the radiator fan switch but that should not have any effect on one or two fans working (per the description in Clark's Garage website) so I tested the fans and both work w/ power from the battery. I took the cover off the dual fan relay and only one relay was energizing. I could manually close the relays and turn on either fan on low or high speed. I thought "must be the relay assembly" so I send off my trusty order to Pelican for a new relay (these things are NOT cheep).

Now, the real fun begins. Yesterday, the UPS guy delivered my relay on time (thanks, Pelican guys) and I rushed right out and plugged it in, started up and turned on the A/C. BIG racket (I've never heard the fans on high speed except for testing) as both fans start on high speed - for about 3 seconds. Then they switch to low speed for about 2 seconds, then back to high and continue to cycle like that. Same thing when I let it idle long enough to have the temp come up and turn on the fans on what should be slow speed - they come on high and start the cycle between high and low. I have not jumpered the thermal switch connections from the radiator to see what happens when the fans should be on high speed.

My question is - has this happened to any of you? Is it just a bad new fan relay? Any other possibilities? I'm out of ideas and this circuit for the fans doesn't seem like rocket science. But then I'm not a rocket scientist.
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Carroll
'89 S2
Old 10-03-2003, 08:00 AM
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The periodic cycling sounds very similar to a problem I had except the period was 7 seconds on, 3 seconds off.

The same question came up on 968.net very recently.

See my comments at http://65.61.16.109/forum/topic.asp?TOPIC_ID=5906

I'd found my solution to this problem at the PCA tech forum:
http://www.pca.org/tech/tech_qa_question.asp?id={F49B658F-B006-4D76-BD60-5566FB114E62}

Karl.
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Previously: 1991 944 S2
Currently: Something from München...
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Old 10-03-2003, 10:46 AM
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Karl,

Thanks a million for the tip. I have no doubt that is what I find when I get in there. When the fans switch to low speed they run at very different speeds probably indicating different resistance values. I'm eager to see it. Is the failsafe circuit part of the relay?
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'89 S2
Old 10-06-2003, 05:52 AM
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I think the temperature failsafe is in the resistor itself.

Karl.
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Previously: 1991 944 S2
Currently: Something from München...
http://www.weissach.net/
Old 10-07-2003, 08:46 AM
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Wink

Just finished repairing the wiring at the resistors and now I have normally working fans again... NO CYCLING!!!

The failsafe circuit must have been non-functional either in or while using the old relay. I pluged it back in and only one fan works and no cycling with it. The resistors were just fine - the copper connectors and wires were corroded from oxidation and some heat (battery fumes?) Seems the connections on the resistors must be s/s as they were clean and bright. $0.99 worth of crimp connectors and a $120 relay to make me smile. Guess I'm easy. Thanks for the help.
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'89 S2
Old 10-08-2003, 04:11 PM
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Where exactly did you find the resistors at? I read the link and suspect that's what's wrong with my NA 944, but can't seem to find the referenced parts.

Sam
Old 10-08-2003, 04:39 PM
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Quote:
Originally posted by Sam Lin
Where exactly did you find the resistors at? ...
If you mean a source, a dealer is the quickest place to look. They're not expensive parts.

If you mean location, read my comments at http://65.61.16.109/forum/topic.asp?TOPIC_ID=5906

Karl.
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Old 10-08-2003, 05:14 PM
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Sam,

What year model do you have? I think the layout and circuit is somewhat different on the early models. Karl's link above describes the physical location very well - sort of behind and inboard of the battery and under the thin black weather cover.

Carroll
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Old 10-09-2003, 05:12 AM
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Mine's an '86 - I wasn't looking remotely near the right place, nor did I know what to look for, as I was looking for a resistor that I thought would be a ceramic rectangle, not a black "hockey puck." I think I got it now.

Thanks!
Sam
Old 10-09-2003, 07:12 AM
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I was looking for black also but they turned out to be a pinkish tan
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Old 10-09-2003, 10:04 AM
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How big of a round "puck" am I looking for?

Sam
Old 10-09-2003, 02:08 PM
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Maybe 2 in. with a screw in the middle.
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Old 10-10-2003, 09:44 AM
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