Hi all,
It looks like the DAC1996 diode pack is no longer available. So I would like to rebuild it. I think it consists of 3 diodes. Two of them look conventional (small black cylinders with a silver ring), though I cannot read any markings on them. The 3rd component looks like an almost-spherical shiny ceramic bulb with a green ring and green triangles. Labeled D3 on the board, so I presume that’s a diode too. Can anyone provide/guess specs for these 3 components? Thanks.
Found this schematic in Kirby’s book. The oddball diode is between 1 and 3.
Looks like a Zener diode. I am not familiar with the diode pack, what does it do?
As far as I understand, it passes power to trigger the relay for the electric cooling fan, and stops the various sources (fan temp switch, A/C compressor switch) from pushing 12V+ at each other. I think it has an additional role if the car has headlight wash/wipe.
Have you got a schematic showing how it is connected?
The Zener could be a free wheeling diode for the relay. It appears to be intact. The other two won’t be critical as long as current and voltage ratings are ok
This is the diagram for my year (1989). That year, looks like the A/C does not trigger the fan. In previous years, that trigger came in through terminal 3. I think I’d like to hook that up too. The Zener tests with the same resistance in both directions (3.5 ohms) – don’t know if that means it’s good or not.
So actually for 1989, the Zener diode does nothing.
Is that the relay from the inner part of the blower fan assembly???
From that diagram It doesn’t make sense to have a Zener diode there. It appears to be there to bypass the thermal switch and turn the fan on even with a cold radiator. So I don’t quite understand why it is different from the other diodes.
The other two are there so the fan can only turn on when the ignition is on, but it can self hold and continue running until the thermal switch turns it off even after the ignition is switched off. I hope the fan relay has an internal freewheeling diode. If it does any diode with 2 or 3A current capability will do as a replacement for the broken ones.
Have you got any source for the diodes? I can check part numbers for you.
Cheers,
Harald
It is called ball ceramic diode. You can find plenty of these, mostly for old tech… It must withstand high temp due to high momentary load, if no markings evident - go by diameter of the ball and connectors to match it with something on the market, alternatively - buy few types and measure the approx voltage drop after connected to f.eg 9v battery
Measuring resistance on the diodes won’t help much. You should measure high impedance in one direction. What you really need is s multimeter with a diode tester.
Our you could connect a light bulb in series with it to the battery. Should light up in one direction and not in the other.
Harry
The idea is to measure diode parameters, not function…
Thanks, guys. XjsBanger, it’s for the rad fan not the blowers fans. Funny that you mention the blowers, I just ordered all the bits to rebuild the control boards for them. Harry, I will have some of these diodes spare (ordered a 10-pack). I think they will do for the diode pack too: “IN5401 Rectifier Diode 3 Amp 100 Volt.”
The fan relay is labelled 4RD, and Moss lists it as “DAC7687 REVERSE INHIBIT RELAY, green” – I presume that is the type with an internal freewheeling diode (not sure what that means) – right?
I think I will disconnect the coolant-activated on/off thermostat, use this variable one instead and install a light at the dash so I can see when it is on: Advance Auto Parts - Down for Maintenance
(Kirby, you mentioned that one in your book – it’s still available and cheap!)
What you measure will depend on the multimeter though. So its not worth a lot. If you want useful information you need to measure the diode characteristic which looks like this.
Terminal 5 in that diagram is part of the “bootstrap circuit”, the circuit that keeps the fan running if the fan switch (“thermostat”) is calling for it when the engine is shut off. Once the fan switch shuts it off, the bootstrap circuit is broken and the fan cannot restart without the ignition on.
Frankly, with the diagram shown, that’s pretty much all this diode pack does. The diode between 2 and 4 prevents the bootstrap circuit from backfeeding the ignition system and keeping the car running! The diode between 4 and 5 prevents the ignition power from directly running the fan, bypassing the fan relay altogether. And as mentioned, the diode between 1 and 3 does nothing here – but it would be a good place to connect up the A/C so the fan runs whenever the compressor is engaged. In that case, the diode would prevent the fan switch from engaging the compressor whenever it turns the fan on. I don’t really see any good reason why that diode would need to be anything special, other than perhaps the compressor clutch is an unusually inductive load.
Why would you replace a coolant temp sensor with an air temp sensor to control the fan?
Maybe the other two have already been replaced and this one hasn’t as it is not used?
The latter is my kind of test…
So I can turn it way down and have the fan come on earlier, also:
A desirable mod would be to allow the fan to kick on anytime the heat-soak raises the under-hood temp to the point where the air thermostat clicks on. Sounds like the stock wiring won’t permit that. What change would be necessary to enable that?