Slight delay normal w/load reduction relay?

[Lance Morgan]

I recently rewired my radiator and A/C cooling fan relay sockets (91
Saab 900S), per a TSB, so that both fans now come on, per the rad
thermoswitch calling, vs just one.

The only info I can provide wrt to the (used) replacement relay is that
it's a 5-pin Cartier, 2 to 3X taller than the stock Bosch 12V 2x15A
relay, purported to be a "12v-50A" (12V but not 50A stamped on side) and
"a load reduction relay"

Testing the circuit, there is about a 1/2 second delay in both turning
the cooling fans on or off (time lag seems equal). Whereas w/the Bosch
relay, for one fan, on/off was virtually instantaneous

Each fan has a distinct 30A fuse

Is this normal behavior, due to the Cartier possibly being a "load
reduction relay" (aren't most/all relays essentially that?), or merely
the start of a sticking relay? The relay is expensive new, but I'll get
one, if needed.


Thank you,
Lance

 

[Bill Kapaun]

I recently rewired my radiator and A/C cooling fan relay sockets (91
Saab 900S), per a TSB, so that both fans now come on, per the rad
thermoswitch calling, vs just one.

The only info I can provide wrt to the (used) replacement relay is that
it's a 5-pin Cartier, 2 to 3X taller than the stock Bosch 12V 2x15A
relay, purported to be a "12v-50A" (12V but not 50A stamped on side) and
"a load reduction relay"

Testing the circuit, there is about a 1/2 second delay in both turning
the cooling fans on or off (time lag seems equal). Whereas w/the Bosch
relay, for one fan, on/off was virtually instantaneous

Each fan has a distinct 30A fuse

Is this normal behavior, due to the Cartier possibly being a "load
reduction relay" (aren't most/all relays essentially that?), or merely
the start of a sticking relay? The relay is expensive new, but I'll get
one, if needed.


Thank you,
Lance

With BOTH fans turning on at the same time, possibly the increased current
draw is causing a temporary voltage drop to both fans.
Unplug one fan and see if the "problem" still appears when just one fan
turns on.

 

[John Gilmer]

With BOTH fans turning on at the same time, possibly the increased current
draw is causing a temporary voltage drop to both fans.
Unplug one fan and see if the "problem" still appears when just one fan
turns on.

Some relays on automobiles are "thermal relays" which use a heat actuated
bi-metal strip as the armature. There are a little slow responding but in
many applications this is desirable. The usually are more efficient than
regular DC relays switching the same power.

I don't know anything about your particular relay, however.

 

[Lance Morgan]

With BOTH fans turning on at the same time, possibly the increased
current
draw is causing a temporary voltage drop to both fans.
Unplug one fan and see if the "problem" still appears when just one
fan
turns on.

Unplugged one fan (actually alternated fans, w/similar response), and
Cartier relay closed/fan ran almost instantaneously when closing rad
thermoswitch.

But fan runs _w/power_ for +1 second _after_ rad thermoswitch contact
opened. Then, after two or three secs of fan coast-down - fan rotation
to complete stop - can hear Cartier relay click open.

Repeated again w/both fans connected: this time both fans ran almost
instantaneously (w/o the earlier lag), then behavior similar to immed
para above (w/relay clicking open after first fan stops)

Possible cause of relay power "hang"?

 

[Tony Williams]

[snip]

Possible cause of relay power "hang"?

Permanent magnet dc-motors are also very good dc-generators.

Any chance that you wired the circuit so that, (on rundown),
the generated emf from either of the fans can keep the relay
coil energised?

+--------------------------+
| Sw |
+12v-+---+/+---+--------+ +---+/+-----+
__|__ __|__ | __|__
| | | | | | |
|Fan1 | |Coil |---------+ |Fan2 |
|_____| |_____| |_____|
| | |
0v-------------+--------+-------------------+

Above is a simple example. When Sw is opened, Fan1 will
generate a rundown emf that keeps the coil energised for
a short while.

If not that simple, there could be other (sneakier) paths
between either fan and the relay coil, eg via a diode.

 

[Fred Bloggs]

[snip]

Possible cause of relay power "hang"?

Permanent magnet dc-motors are also very good dc-generators.

Any chance that you wired the circuit so that, (on rundown),
the generated emf from either of the fans can keep the relay
coil energised?

+--------------------------+
| Sw |
+12v-+---+/+---+--------+ +---+/+-----+
__|__ __|__ | __|__
| | | | | | |
|Fan1 | |Coil |---------+ |Fan2 |
|_____| |_____| |_____|
| | |
0v-------------+--------+-------------------+

Above is a simple example. When Sw is opened, Fan1 will
generate a rundown emf that keeps the coil energised for
a short while.

If not that simple, there could be other (sneakier) paths
between either fan and the relay coil, eg via a diode.

I don't see how it's possible to miswire- but that's exactly what he's
done. The 5-pin is an isolated coil and a SPDT. All he has to figure out
is that the thermoswitch is in series with the coil- there should be no
other wire that joins with the thermoswitch/coil terminal connection.
The "load reduction relay" refers to a relay which de-energizes
everything but the starter with ignition in start position- has nothing
to do with reducing sensor loading like he thinks.

Please view in a fixed-width font such as Courier.




RIGHT WAY

+------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+---------------+--------+ |
| | | | | | |
| (-)---(+) | | | +------+ |
--- | | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | thermo |
+---------+ start | sw |
|ignition |----+ | +-----o o----+ |
| sw | +-----------+ | --- +--------------+
+---------+ | | NC | NO| | +-- | | NO | NC|
| ) o o | | T | | ) o o |
load | ) | | | --+ | ) --> / |
reduction | ) o | | | ) o |
relay | | COM| | | | | COM| |
| | +----|-+ | +-------+ |
+-----------+ +--------------+
| |
| |
--- ---
/// ///




RIGHT WAY +------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+------------------------+ |
| | | | | |
| (-)---(+) | | +------+ |
--- | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | |
| | |
| +----------+ |
| +--------------+
| | | NO | NC|
| | ) o o |
+---------+ start | ) --> / |
|ignition |----+ +-----------+ | ) o |
| sw | +------+----+ | | | COM| |
+---------+ | | NC | NO| | | | | |
| ) o o | | +-|-------|----+
load | ) | | | | |
reduction | ) o | | thermo| ---
relay | | COM| | | sw | ///
| | +----|--+ +---o o-+
+-----------+ | ---
| | +--
+------------+ T |
--- --+
///





RIGHT WAY +------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+------------------------+ |
| | | | | |
| (-)---(+) | | +------+ |
--- | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | |
| | |
| +----------+ |
| +--------------+
| | | NO | NC|
| | ) o o |
+---------+ start | ) --> / |
|ignition |----+ +-----------+ | ) o |
| sw | +------+----+ | | | COM| |
+---------+ | | NC | NO| | | | | |
| ) o o | | +-|-------|----+
load | ) | | | | |
reduction | ) o | +---------------+
relay | | COM| | |
| | +----|--+ |
+-----------+ | thermo|
| | sw |
+------------+-------o o-+
--- ---
/// +--
T |
--+



RIGHT WAY +------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+------------------------+ |
| | | | | |
| (-)---(+) | | +------+ |
--- | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | |
| | |
| +----------+ |
+---------------+ | +--------------+
| | | | | NO | NC|
| | | | ) o o |
+---------+ start | | | ) --> / |
|ignition |----+ | | | ) o |
| sw | +------+----+ | | | COM| |
+---------+ | | NC | NO| | | | | |
| ) o o | | +-|-------|----+
load | ) | | | | |
reduction | ) o | | +---------------+
relay | | COM| | | | |
| | +----|---+ | |
+-----------+ | thermo|
| | sw |
+----------------+---o o-+
--- ---
/// +--
T |
--+

 

[Tony Williams]

Below is your last diagram Fred. There's something wrong
with it...... the contacts of the load reduction relay
don't do anything. Maybe the connection from +BATT to the
fans should be opened?

 

[Lance Morgan]

[snip]

Possible cause of relay power "hang"?

Permanent magnet dc-motors are also very good dc-generators.

Any chance that you wired the circuit so that, (on rundown),
the generated emf from either of the fans can keep the relay
coil energised?

+--------------------------+
| Sw |
+12v-+---+/+---+--------+ +---+/+-----+
__|__ __|__ | __|__
| | | | | | |
|Fan1 | |Coil |---------+ |Fan2 |
|_____| |_____| |_____|
| | |
0v-------------+--------+-------------------+

Above is a simple example. When Sw is opened, Fan1 will
generate a rundown emf that keeps the coil energised for
a short while.

If not that simple, there could be other (sneakier) paths
between either fan and the relay coil, eg via a diode.

I don't see how it's possible to miswire- but that's exactly what he's
done. The 5-pin is an isolated coil and a SPDT. All he has to figure
out
is that the thermoswitch is in series with the coil- there should be
no
other wire that joins with the thermoswitch/coil terminal connection.
The "load reduction relay" refers to a relay which de-energizes
everything but the starter with ignition in start position- has
nothing
to do with reducing sensor loading like he thinks.

Please view in a fixed-width font such as Courier.




RIGHT WAY

+------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+---------------+--------+ |
| | | | | | |
| (-)---(+) | | | +------+ |
--- | | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | thermo |
+---------+ start | sw |
|ignition |----+ | +-----o o----+ |
| sw | +-----------+ | --- +--------------+
+---------+ | | NC | NO| | +-- | | NO | NC|
| ) o o | | T | | ) o o |
load | ) | | | --+ | ) --> / |
reduction | ) o | | | ) o |
relay | | COM| | | | | COM| |
| | +----|-+ | +-------+ |
+-----------+ +--------------+
| |
| |
--- ---
/// ///


other RIGHT WAYS snipped

Wow guys - the tremendous help & schematics! are much appreciated.

This is the bulletin/wiring diagram I followed: this site has been down
for several days (has twice changed its base URL in last few wks) but
appears back up this a.m.

http://216.78.172.20/cooling_system_folder/hightempsbpg1.htm

[not shown on diagram is rad thermoswitch 39: comes off pull-down pin 85
of relay 396; other side grounded. Pull-down pin 86 connected to pin 30
on relay 156]

I just rechecked - it appears that I've followed the bulletin to a T
(famous last words!)


37 = main cooling fan

155 = J position Cartier relay ("12v-50A")

156 = H position Bosch 12V 2x15A relay (155 was previously the same
relay])

172 = A/C cooling fan

396 = also Bosch 12V 2x15A relay

After fan 37 rundown, Cartier relay opens


Other circuit changes, previous to above mod: A/C compressor has been
removed.

166 = A/C pressure switch bypassed and sockets jumpered closed.

168 = A/C temp coolant switch intact and always closed unless overheat
occurs

169 = A/C dash switch/button

170 = A/C compressor and 173 diode removed: two respective grnds beneath
_not_ intact (restoring grounds would cause a short at 156 relay / 87b,
when pulled down ... right?)

171 = A/C "antifreeze" switch in closed position

 

[Lance Morgan]

Lance Morgan wrote:
snip

http://216.78.172.20/cooling_system_folder/hightempsbpg1.htm

[not shown on diagram is rad thermoswitch 39: comes off pull-down pin
85
of relay 396; other side grounded. Pull-down pin 86 connected to pin
30
on relay 156]

I just rechecked - it appears that I've followed the bulletin to a T
(famous last words!)


37 = main cooling fan

155 = J position Cartier relay ("12v-50A")

156 = H position Bosch 12V 2x15A relay (155 was previously the same
relay])

172 = A/C cooling fan

396 = also Bosch 12V 2x15A relay

After fan 37 rundown, Cartier relay opens


Other circuit changes, previous to above mod: A/C compressor has been
removed.

166 = A/C pressure switch bypassed and sockets jumpered closed.

168 = A/C temp coolant switch intact and always closed unless overheat
occurs

169 = A/C dash switch/button

170 = A/C compressor and 173 diode removed: two respective grnds
beneath
_not_ intact (restoring grounds would cause a short at 156 relay /
87b,
when pulled down ... right?)

171 = A/C "antifreeze" switch in closed position

p.s. 200 = ECU / computer

 

[Fred Bloggs]

Oh yeah- you're right- hazards of ASCII art cut-n-paste. That case was
meant to cover the load reduction relay breaking the normally closed
connection of Vbatt to both the fan high side and the thermoswitch/relay
coil in parallel. You can see in this particular case that if he
connects fan control relay COM to bottom coil contact instead of GND, he
ends up the fan run-on problem:

Please view in a fixed-width font such as Courier.



RIGHT WAY +------+
+------| FAN |----+
| +------+ |
| |
+------+ +--+ | |
| | | | | |
| (-)---(+) | | +------+ |
--- | | | +------| FAN |----+
/// | BATT | | | +------+ |
+-------+ | | |
| | |
| | |
| +----------+ |
+---------------+ | +--------------+
| | | | | NO | NC|
| | | | ) o o |
+---------+ start | | | ) --> / |
|ignition |----+ | | | ) o |
| sw | +------+----+ | | | COM| |
+---------+ | | NC | NO| | | | | |
| ) o o | | +-|-------|----+
load | ) | | | | |
reduction | ) o | | +---------------+
relay | | COM| | | | |
| | +----|---+ | |
+-----------+ | thermo|
| | sw |
+----------------+---o o-+
--- ---
/// +--
T |
--+

 

[Lance Morgan]

[snip]

Possible cause of relay power "hang"?

Permanent magnet dc-motors are also very good dc-generators.

Any chance that you wired the circuit so that, (on rundown),
the generated emf from either of the fans can keep the relay
coil energised?

+--------------------------+
| Sw |
+12v-+---+/+---+--------+ +---+/+-----+
__|__ __|__ | __|__
| | | | | | |
|Fan1 | |Coil |---------+ |Fan2 |
|_____| |_____| |_____|
| | |
0v-------------+--------+-------------------+

Above is a simple example. When Sw is opened, Fan1 will
generate a rundown emf that keeps the coil energised for
a short while.

If not that simple, there could be other (sneakier) paths
between either fan and the relay coil, eg via a diode.

I will try to work up another composite wiring mod, based on your and
Fred's schematics [3 relays may be 2 too many for me!]

In the meantime, is having the coil emf-energized potentially harmful to
the circuit or any components?

 

[Tony Williams]

http://216.78.172.20/cooling_system_folder/hightempsbpg1.htm

From that circuit diagram, it looks like the rundown-emf from
Fan37 could keep the coil of Relay155 energised for a short
while (via the spliced connection).

So there is probably no mistake in your wiring and you have
simply detected an undocumented 'feature' of Saab's mod.

It doesn't look as though the rundown emf will cause damage,
and presumably Saab are not worried about it. So perhaps
you need not worry about it.


There is something in the circuit I can't understand though.

Relay396 energises the main fan, with it's coil switched
by the rad thermoswitch. Ok, no prob with that.

But Relay156 can also energise the main fan, with it's coil
switched by something unspecified. So what is it that turns
Relay156 on?

 

[Lance Morgan]

From that circuit diagram, it looks like the rundown-emf from
Fan37 could keep the coil of Relay155 energised for a short
while (via the spliced connection).

So there is probably no mistake in your wiring and you have
simply detected an undocumented 'feature' of Saab's mod.

It doesn't look as though the rundown emf will cause damage,
and presumably Saab are not worried about it. So perhaps
you need not worry about it.


There is something in the circuit I can't understand though.

Relay396 energises the main fan, with it's coil switched
by the rad thermoswitch. Ok, no prob with that.

But Relay156 can also energise the main fan, with it's coil
switched by something unspecified. So what is it that turns
Relay156 on?

The only thing I can see is ECU 200. However, I disconnected the jumper
that I had at A/C pressure sw 166 - as A/C has been removed - and there
was curiously no change in the fan(s) behavior. I'll investigate 166 &
200 some more. I have some ECU pin-out info, but alas is incomplete.
More on "Diode or MOSFET" thread

 

[Fred Bloggs]

From that circuit diagram, it looks like the rundown-emf from
Fan37 could keep the coil of Relay155 energised for a short
while (via the spliced connection).

So there is probably no mistake in your wiring and you have
simply detected an undocumented 'feature' of Saab's mod.

It doesn't look as though the rundown emf will cause damage,
and presumably Saab are not worried about it. So perhaps
you need not worry about it.


There is something in the circuit I can't understand though.

Relay396 energises the main fan, with it's coil switched
by the rad thermoswitch. Ok, no prob with that.

But Relay156 can also energise the main fan, with it's coil
switched by something unspecified. So what is it that turns
Relay156 on?

It looks something like this:
Please view in a fixed-width font such as Courier.




RIGHT WAY





+---+ +-------------+-----------------+-----------------+
| | | | | |
| (-)---(+) | o a/c |
--- | | | / sw |
/// | BATT | | o |
+-------+ | | |
+----|-----------------|-----------------+
| | | |
| | | |
| +------------+ | |
| | | | |
+-------------------------------------+--|>|----+ |
| | | | | |
| | | 156 396 | +--|>|----+ | 155
| 200 +-----------+ +-----+ | +-|------------+
| thermo | | NO | | |NO | | | | | NO | |
| sw | ) o | | o | | | ) o |
+---o o---+ | ) / | | / | | | ) --> / |
--- | | ) o | | o | | | ) o |
+-- | | | COM| | |COM| | | | | COM| |
T | | | | | | | | | | | | | |
--+ | +-----------+ +-----+ | +--------------+
| | | | | | |
+----+ | | | | |
+------------+----+ --- |
| /// |
| 37 | 172
| MAIN | A/C
+------+ +------+
| FAN | | FAN |
+------+ +------+
| |
| |
--- ---
/// ///

So you can see that the a/s switch will turn the main fan off and
relay396 prevents this- taking over the 156 contact path ust to the main
fan and not that other gizmo labeled "K".

 

[Fred Bloggs]

It looks something like this:
Please view in a fixed-width font such as Courier.




RIGHT WAY





+---+ +-------------+-----------------+-----------------+
| | | | | |
| (-)---(+) | o a/c |
--- | | | / sw |
/// | BATT | | o |
+-------+ | | |
+----|-----------------|-----------------+
| | | |
| | | |
| +------------+ | |
| | | | |
+-------------------------------------+--|>|----+ |
| | | | | |
| | | 156 396 | +--|>|----+ | 155
| 200 +-----------+ +-----+ | +-|------------+
| thermo | | NO | | |NO | | | | | NO | |
| sw | ) o | | o | | | ) o |
+---o o---+ | ) / | | / | | | ) --> / |
--- | | ) o | | o | | | ) o |
+-- | | | COM| | |COM| | | | | COM| |
T | | | | | | | | | | | | | |
--+ | +-----------+ +-----+ | +--------------+
| | | | | | |
+----+ | | | | |
+------------+----+ --- |
| /// |
| 37 | 172
| MAIN | A/C
+------+ +------+
| FAN | | FAN |
+------+ +------+
| |
| |
--- ---
/// ///

So you can see that the a/s switch will turn the main fan off and
relay396 prevents this- taking over the 156 contact path ust to the main
fan and not that other gizmo labeled "K".

So the a/c always turned both fans on -but the thermoswitch only turned
on main- the series combination of the relay coils activates 156 but not
155. The mod is to get both fans on with the thermo switch- but they
have to prevent 396 from latching it on. So there must be something up
with that Cartier 155 coil input taps so that both the current supplied
from the series 156 coil path AND the current supplied through 396
contacts are required to maintain 155 on. Then the thermoswitch
ultimately controls both fans. This would make sense.

 

[Lance Morgan]

So the a/c always turned both fans on -but the thermoswitch only
turned
on main- the series combination of the relay coils activates 156 but
not
155. The mod is to get both fans on with the thermo switch- but they
have to prevent 396 from latching it on. So there must be something up
with that Cartier 155 coil input taps so that both the current
supplied
from the series 156 coil path AND the current supplied through 396
contacts are required to maintain 155 on. Then the thermoswitch
ultimately controls both fans. This would make sense.

I thought I was looking at my Bentley service manual wiring diagrams for
a second

K = 170 = A/C compressor (which has been removed)

 

[Fred Bloggs]

I thought I was looking at my Bentley service manual wiring diagrams for
a second

K = 170 = A/C compressor (which has been removed)

Okay then this is coming together like so:
Please view in a fixed-width font such as Courier.




RIGHT WAY





+---+ +--------+--------------------+-------------------+
| | | | +---+ |
| (-)---(+) | | o | 166 |
--- | | | |/ | THERMO SW |
/// | BATT | | | o | |
+-------+ | +---+ |
+----|--------------------|-------------------+
| | | |
| | | |
| | | |
| | | |
+----------------------------------------+---|>|-----+ |
| | | | |
| | | +---------------|>|-+ | |
| | | | | | |
| | +----------------------+ | | |
| 171 | | 156 | 396 | | | | 155
| + +----------+ | +--------------------------+
| 200 | | | | | | | | | | |
| TSTAT | ) +-+ | | | o K1) K2) o |
+---o o---+ | ) o o | | | / ) ) / |
--- | | ) / / | | | o ) ) o |
+-- | | | o o | | | | | | | |
T | | | | | | | | | | +---+ | |
--+ | +----------+ | +--------------------------+
| | | | | | | |
+----+ | | | | | |
| +--------+-------------+ --- |
+-----+ | /// |
| | 37 | 172
| | A/C | MAIN
+----+ +------+ +------+
| K | | FAN | | FAN |
+----+ +------+ +------+
| | |
+-------+ |
--- ---
/// ///

The radiator thermoswitch is the box 166 labeled R, and assemblies 171
and 200 are a/c thermostat and maybe an overpressure cutout
respectively. The sw166 energizes relays contacts 396 and 155 and forces
156 off. So the thermo switch turns on both fans and cuts the compressor
off. The full battery voltage on coil K1 alone is not enough to keep the
relay on so that it turns off when sw166 opens. When the radiator is not
in overtemp, then the a/c thermostat connects the bottom of the 156 coil
in series with K2 and this activates relay 156 throwing voltage to fan
37 and the compressor. This also puts battery voltage on K1 which
together with the current through K2 turns relay 155 on and puts voltage
on main fan 172. When TSTAT opens, this cuts current to K2 so relay 155
drops out. The dropout delay is caused by a/c fan 37 motoring current
into coil K1.

 

[Tony Williams]

It looks something like this:
Please view in a fixed-width font such as Courier.

+BATT-------+-----------------+-----------------+
| | |
| o a/c |
| / sw |
| o |
| | |
+----|-----------------|-----------------+
| | | |
| | | |
| +------------+ | |
| | | | |
+-------------------------------------+--|>|----+ |
| | | | | |
| | | 156 396 | +--|>|----+ | 155
| 200 +-----------+ +-----+ | +-|------------+
| thermo | | NO | | |NO | | | | | NO | |
| sw | ) o | | o | | | ) o |
+---o o---+ | ) / | | / | | | ) --> / |
--- | | ) o | | o | | | ) o |
+-- | | | COM| | |COM| | | | | COM| |
T | | | | | | | | | | | | | |
--+ | +-----------+ +-----+ | +--------------+
| | | | | | |
+----+ | | | | |
+------------+----+ --- |
| /// |
| 37 | 172
| MAIN | A/C
+------+ +------+
| FAN | | FAN |
+------+ +------+
| |
| |
--- ---
/// ///

So you can see that the a/s switch will turn the main fan off and
relay396 prevents this- taking over the 156 contact path ust to
the main fan and not that other gizmo labeled "K".

No, I think that circuit is wrong Fred. "200" is not the
thermoswitch, it is the ECU (Engine Control Unit?).

The gizmo labelled K is probably a solenoid that engages the a/c
compressor. It is powered via Relay156. The ECU (only) drives the
coil of 156, probably engaging/disengaging the a/c compressor
according to the required internal temperature setting. It is
also probable that the ECU does not engage the a/c compressor
unless the engine is running. Presumably the compressor puts a
significant load on the engine, so the second contact on 156
does a pre-emptive turnon of the radiator cooling fan.

But they also need normal temperature-sensed radiator cooling,
which is done by Relay396, whose contacts are in parallel
with 156.

The coil of 396 is not drawn on that Saab diagram, but has
been previously described as having the top end supplied with
+BATT (from terminal 30 of Relay156) and it's bottom end
going to ground via the thermoswitch. This is the only relay
that the thermoswitch drives.

The aircon was almost certainly an optional extra. If not
fitted, Relays 156 and 155 would not even be present, just
Relay 396.

 

[Fred Bloggs]

No, I think that circuit is wrong Fred. "200" is not the
thermoswitch, it is the ECU (Engine Control Unit?).

The gizmo labelled K is probably a solenoid that engages the a/c
compressor. It is powered via Relay156. The ECU (only) drives the
coil of 156, probably engaging/disengaging the a/c compressor
according to the required internal temperature setting. It is
also probable that the ECU does not engage the a/c compressor
unless the engine is running. Presumably the compressor puts a
significant load on the engine, so the second contact on 156
does a pre-emptive turnon of the radiator cooling fan.

But they also need normal temperature-sensed radiator cooling,
which is done by Relay396, whose contacts are in parallel
with 156.

The coil of 396 is not drawn on that Saab diagram, but has
been previously described as having the top end supplied with
+BATT (from terminal 30 of Relay156) and it's bottom end
going to ground via the thermoswitch. This is the only relay
that the thermoswitch drives.

The aircon was almost certainly an optional extra. If not
fitted, Relays 156 and 155 would not even be present, just
Relay 396.

Okay- after decoding one of the original posts it looks like this:

Please view in a fixed-width font such as Courier.

+---+ +--------+--------------------+-------------------+
| | | | +-|-+ |
| (-)---(+) | | o | 169 |
--- | | | |/ | A/C DASH |
/// | BATT | | | o | SW |
+-------+ | +-|-+ |
+----|--------------------|-------------------+
| | | |
| | | |
| | | | 155
| | | +----------------+
+---------------------------------------+-----------|>|-+ | |
| | | | | | |
| | | +-----------------------|>|-+ | |
| | | | | | | |
| | +---------------+----+ | | | |
| | | 156 | 396| | | | | |
| +--|--------+ | +--|------+ | | | |
| 200 | | | | | | | | | | | | |
| | K) +-+ | | | K) o | | K) o |
+------+ | ) o o | | | ) / | | ) / |
| ---| | ) / / | | | ) o | | ) o |
| +-| | | o o | | | | | | | | | |
| T | | | | | | | | | | | | | | | |
| --+ | +--|--------+ | +--|------+ +-------|--------+
| | | | | | | | | |
| +--|-------+ | | | | | | |
| o | | +--------+------|----+ --- |
| / | +-----+ | | /// |
| o | | | 37 +-|-+ | 172
| | | |170 | A/C | o | 39 | MAIN
+------+ +----+ +------+ |/ | THERMO +------+
| | K | | FAN | | o | SW | FAN |
| +----+ +------+ +-|-+ +------+
| | | | |
+-------+-------+---------------+ |
--- ---
/// ///


The ecu200 has to gnd the other end of 156-K since they say that's a 12V
Bosch. The a/c keeps main172 running continuously with the ac37 and
ac170 cycled by the tstat in ecu200- which also senses presence of the
12V through the pressure and temperature switches. thermo396 now
switches both fans on which was the main problem before where it only
turned on the a/c fan apparently- but they left that problem with 155-K
directly across the ac37 -causing the run-on. The simplest way to fix
the run-on is to add an el-cheapo relay XXX in parallel with 396 like shown:
Please view in a fixed-width font such as Courier.


+---+ +--------+--------------------+-------------------+
| | | | +-|-+ |
| (-)---(+) | | o | 169 |
--- | | | |/ | A/C DASH |
/// | BATT | | | o | SW |
+-------+ | +-|-+ |
+----|--------------------|-------------------+
| | | |
| | | |
| | | | 155
| | | +--------------+
+---------------------------------------+-----------|>|-+ | |
| | | | | | |
| | | +----|>|-+ | |
| | | | | | | |
| | +---------+--+-------+--+ | | | | |
| | | 156 396| | XXX| | | | | | |
| +--|--------+ +--|--|-+ +--|--|-+ | | | | |
| 200 | | | | | | | | | | | | | | | | |
| | K) +-+ | | K) o | | K) o | | | K) o |
+------+ | ) o o | | ) / | | ) / | | | ) / |
| ---| | ) / / | | ) o | | ) o | | | ) o |
| +-| | | o o | | | | | | | | | | | | | |
| T | | | | | | | | | | | | | | | | | | | |
| --+ | +--|--------+ +--|--|-+ +--|--|-+ | -+-----|--------+
| | | | | | | | | | | |
| +--|-------+ | | | | | +---+ | |
| o | | | +----------+ --- |
| / | | | | | /// |
| o | | +---------|--+ | 172
| | | +-----+ | | | MAIN
+------+ | | 37 +-|-+ +------+
| |170 | A/C | o | 39 | FAN |
| +----+ +------+ |/ | THERMO +------+
| | K | | FAN | | o | SW |
| +----+ +------+ +-|-+ |
| | | | ---
+-------+-------+---------+ ///