Second condenser fan for D2

Disco Andy

Member
Oct 7, 2020
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MD
I would welcome any suggestions for wiring up a second condenser fan for keeping the engine cool under severe load.
ideally the control circuit will be coolant temperature based say switch on at 215 d. Alternatively it can be manual on a switch.
so 2 questions:
1. Is there a spare circuit in the engine compartment fuse box for wiring the power circuit ?
2. Is there a way to get the Obdi lubricant temperature to switch a relay at a set temperature for use in the control circuit?
3. If 2., is not easy a good way to wire up the control circuit to the switches near instrument panel.
thanks
The fan is 80 watts so about 6 amps

many thanks !
 

robertf

Well-known member
Jan 22, 2006
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358
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this is a band aid. If its running warm fix the problem correctly.

#1, don't know.
#2 yes, but its tricky and the ISO protocol takes an init and some logic to shutdown or you get a dead battery after a few days like some scangauge users experience. It would never be as instantaneous as I think a system like this should be, and would require removal if a scan tool or inspection equipment is used.
#3, a better way would be to tap into the coolant gauge line from the ECU. Its a fixed frequency and duty cycle is linear with temp. You'll have to experiment to get the corresponding DC to temp table, I think a few points are listed in RAVE. Bonus feature would be to intercept it completely and output a scaled signal to get the temp gauge to move at a more appropriate temperature.
 

Disco Andy

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Oct 7, 2020
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Thanks RobertF
On #2 ,#3?: I was thinking of the source of the OBDI rather than the plug pin out. Wouldn’t that be a digital output of the temp.
Great idea ! - tapping into the coolant temp gauge line. If duty cycle is linear with temperature is it the gauge that is non linear and for many of us misleading?
2-1.where would I find the coolant temp gauge line?
2-2. what is a good way to transform the duty cycle to a analog voltage and then control a relay at a chosen voltage? Maybe there is a better way.
Thanks !
 

robertf

Well-known member
Jan 22, 2006
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I'd just sample it with a microcontroller, but the analog way would be to do something like this
and replace M1 with an op amp to compare the output with another setpoint that matches the on voltage. Then you can do op amp things to account for hysteresis.

the gauge cluster circuit board takes the linear signal and transforms it into useless gauge movements.
 

WaltNYC

Well-known member
Mar 3, 2010
707
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NYC
FYI...from the GEMS OBD manual....
ECT voltage 0.059 V = 145 deg C (293 deg F)
ECT voltage 4.922 V = -40 deg C ( - 40 deg F)

gems_obd is in the google link. Page 65
 

robertf

Well-known member
Jan 22, 2006
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my bad, its frequency not DC

Coolant temperature gauge signal
The ECM controls the temperature gauge in the instrument cluster. The ECM sends a coolant temperature signal to
the temperature gauge in the instrument cluster in the form of a PWM square wave signal.
The frequency of the signal determines the level of the temperature gauge.
Conditions
The ECM operates the PWM signal under the following parameters:
l -40 °C (-40 °F) = a pulse width of 768 µs.
l 140 °C (284 °F) = a pulse width of 4848 µs.

Something like this instead of the linked circuit
 

robertf

Well-known member
Jan 22, 2006
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Rave is contradicting itself, it is DC. I'm pretty sure its 200hz

The ECM also illuminates the high engine
coolant temperature warning lamp when it detects the PWM duty cycle to the temperature gauge is out of range. If it
is greater than 94% duty cycle when the engine is hot, or less than 8% duty cycle when the engine is cold, the engine
coolant temperature gauge pointer will indicate cold, thus alerting the driver with an additional visible warning.
When the ignition is switched on, the ECM illuminates the LED to provide a self-check, providing there is no fault it
will remain illuminated for 3 seconds or until the ignition is switched off.
The response of the engine high temperature warning lamp varies according to engine type and market, there are
three conditions:
l V8 - Gulf.
l V8 - all markets except Gulf.
l Diesel - all markets.
The vehicle configuration determines which condition is set.
The PWM duty cycle thresholds for illuminating and extinguishing the warning lamp are given in the table below.
The power input for the LED is supplied by the instrument pack via fuse 27. The ECM controls the earth path to
illuminate the warning lamp.
MarketLamp onLamp off
V8 - Gulf79.8 ± 2%77.8 ± 2%
V8 - all markets except Gulf77.8 ± 2%75.7 ± 2%
Diesel - all markets78.8 ± 2%76.8 ± 2%
 

Disco Andy

Member
Oct 7, 2020
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MD
Looks like the two paths for control are:

1. The 200Hz PWM @12 V with pulse width:
l -40 °C (-40 °F) = a pulse width of 768 µs.
l 140 °C (284 °F) = a pulse width of 4848 µs.

2.OBD
ECT voltage 0.059 V = 145 deg C (293 deg F)
ECT voltage 4.922 V = -40 deg C ( - 40 deg F)

where would each of these be tapped from?

Microcontroller will be an elegant solution.
Is there simpler hardwired solution
Thanks guys!


The other question is the power circuit.
where can we tap off a fused 10 amp or 15 amp from the engine fuse box?
 

K-rover

Well-known member
Jan 15, 2010
2,163
62
Raleigh, NC
Fwiw, I wired up the existing condenser fan to a switch for the same reason. It still would turn on automatically, but I added a switch in the cab.
It didn't make a bit of difference in temps. Im wondering if I replace the factory condenser with a larger unit if it would make a difference? Or have 2 fans? Let us know if it actually works!
 

Disco Andy

Member
Oct 7, 2020
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0
MD
Thank you WaltNYC and RobertF for the control circuit ideas.
Little more research on the power circuit. Two candidates:
1. Auxiliary circuit relay R7 in engine box which is switched on with ignition switch powers aux power sockets in inside fuse box. Try to tap into it.
2. Fuse F5 that feeds the coolant fan. Try to tap into the line ahead of the coolant fan relay.
K-rover. Sorry to hear the manual switch for the condenser fan didn’t help with the cooling. Perhaps it really needs a second fan and a higher cfm? Anyhow I will report back if I get there.
 

JohnB

Well-known member
Oct 18, 2007
2,292
12
Oregon
Build a relay and use the ac plug to run the ac fan whenever the ac is on. Its a negative on/off if I remember correctly. Still won't help much.