Re: After-run relay diagnostics

[mike posner <posne@cts.com>]

At 12:10 PM 5/30/97 -0500, Luis Marques wrote:
>All this talk about sensors and senders prompted me to do some snooping
>around the wiring in my car ('87 4kcsq) and I discovered that, in fact,
>it had the after-run feature for the radiator fan.  I had never seen it
>in action, so i decided to investigate.
>
>This relay is located on the auxiliary relay panel under the fuse panel
>(at least on the '87 4kq's).  It has five pins labeled "30", "31", "87",
>"15", and "T".  It also has a sixth pin, but is not connected to
>anything.  It should receive battery power all the time trough pin 30. 
>Pin 31 should be grounded all the time.  Pin 15 receives battery power
>from the wiper relay when the ignition is on.  Pin 87 sends power to the
>radiator fan.  Finally, pin "T" goes to ground through the after-run
>switch on the valve cover.
>
>The relay has a timer so that the fan only runs for a fixed amount of
>time after the engine is shut off and its warm.  It works using a
>discharging capacitor.  When the engine is on, this capacitor is charged
>from the power supplied into pin 15 from the wiper relay.  Once the
>engine is turned off, if the engine is warm enough to close the
>after-run switch, this relay will turn on the radiator fan and begin
>discharging the capacitor.  Once the capacitor is discharged, the relay
>opens and the rad. fan is turned off and will remain off until the car
>is used again.  Note that if the wiper relay is bad or missing, the
>after-run feature is disabled!
>
>It turns out that there was nothing wrong with my relay!  It just wasn't
>getting battery power in pin 30.  This pin feeds to a 4mm red wire that
>is connected to a bus under the fuse panel that is connected directly to
>the battery.  I connected this big wire back into the bus and presto!
>the relay works again.  Now the only thing left to do is find out if the
>after run switch is good or bad, since I have yet to hear the fan after
>shutting off the engine.  Either the engine hasn't gotten warm enough to
>trigger this switch, or it has failed open.  Does anybody know how often
>these switches fail? 
>As I recall, there was a recent post on this switch.  I replaced both this
one and the other switch for the f/i fan (located near the wastegate)
because I never heard either go on.  If I Had it to do over again I would
have dunked the sensor end in hot water
probably close to 212f , and taken a continuity check. I recall that the
threshold for the radiator fan is higher than that for the f/i fan to come
on so it has to be a hot day to hear the big fan go off.  You can tell each
by a distinctive sound.

>I hope this info is usefull to others on the list.
>
>  Luis Marques
>  marques@ti.com
>  '874kcsq
>
>