Slight delay normal w/load reduction relay?

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

Reply to
Lance Morgan
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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.

Reply to
Bill Kapaun

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.

Reply to
John Gilmer

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"?

Reply to
Lance Morgan
[snip]

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.

Reply to
Tony Williams

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 | --+

Reply to
Fred Bloggs

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?

Reply to
Tony Williams

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
Reply to
Lance Morgan

Lance Morgan wrote: snip

p.s. 200 = ECU / computer

Reply to
Lance Morgan

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 | --+

T> >

Reply to
Fred Bloggs

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?

Reply to
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?

Reply to
Tony Williams

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
Reply to
Lance Morgan

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".

Reply to
Fred Bloggs

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.
Reply to
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)

Reply to
Lance Morgan

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.
Reply to
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.

Reply to
Tony Williams

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 | | +----+ +------+ +-|-+ | | | | | --- +-------+-------+---------+ /// --- ///

Reply to
Fred Bloggs

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