Re: After-run relay diagnostics

[James Marriott <marriott@lesbois.com>]

Haudi,

Another after-run data point.

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.

My '87 4kq's (8.5:1 2.2, left side rad) fan has run up to _three times_.
The '86 4ks's (10.0:1 1.8 l, full-width rad, two fans, one motor) has
_never_ run, even though it has a "fan may start at anytime" sticker. Go
figure.

> 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.

FWIW, mine will run in 60 dF temps, at 11 PM, after driving the last two
miles home at 30 MPH through residential zones. Can't imagine you can't
beat this in Texas. BTW, I'm working on a two-speed option for my fan
(imagine the fan at full speed at 11 PM in a neighborhood...).

cu
James

PS Nice bit of detective work with the "Pin XX" post.