Test a Relay

[RWebb]

I'd like to test a relay used on a VW Vanagon to troubleshoot a cranks, but will not start condition.

The numbers marked on it, followed by the DIN definitions, are:

30 - direct line from battery +
87 - Input (under the heading "Normally Closed Relay Contact & Changeover Circuits")

then, there are 2 terminals listed under the heading "Switching Relay":
85 - Output: Actuator (Negative Winding End or Ground)
86 - Start of Winding

The diagram on the face of the relay indicates there is a diode in there, so I want to make sure I don't blow it.

1st - can I trust VW to follow the DIN specs? (I ask b/c they have a known habit of going their own way with wire color coding, i.e. brown wires)

2nd - my plan is to put a multimeter on resistance/continuity mode across two terminals, and then apply +12 V - but I am not sure if pin 85 is ground or 87 is?? or what...





my guess is that pin 85 is ground and the big "24" they stamped on there obscures the other end of what would be a normal schematic for a relay - but it's a Foolkswagon, so who knows WTF they did...

any ideas?

[john70t]

Four-Terminal relays are very easy:
1). There are 2 bigger pins which is the load-circuit.
-The "heavy juice" goes through this just like a normal wire.
-This circuit is usually "open" until the control side is energized.

Use the OHM function of a DVOM.
The OHM function is usually safe to use on most big electronics. It sends milliamps across the terminals to find what level of continuity exists.
(Do not use this on live circuits, or you'll blow the meter!!!)

2). There are 2 smaller pins which is the control-circuit.
-Voltage is sent through this by the electronics or manual switches in the dash/pedals.
-Using the OHM function, there should be some continuity.

Basically a relay is a mechanical switch.
When a small amount of juice is sent through the control-side coils in the relay, it pulls a mechanical switch of the load-side closed.
Heavy juice then flows through the relay to operate motors and whatnot.

[fastfredracing]

The very first thing I would do would be to switch the positions of those two relays, and see if what did not work before, now works, and what did work before, now does not.
But basically , one pin of the relay will be grounded when commanded on, , it is either 85, or 86, I cannot remember which one. Once this pin is grounded, it will now pass current between 87&30. One of the latter will already have battery voltage. I would test in situ, and probably have to have the key on.
What circut do these two relays power up?

[1990C4S]

Pull the relay and put 12 vdc across 85 and 86.

Measure (ohms) across and 87. The resistance should be 'zero' with the relay activated, and 'open' with the relay unactivated.

If you hear it click under power the odds are it is fine.

[RWebb]

Measure (ohms) across 30 and 87?

of terminals 85 & 86, which terminal get +12 and which is - (gnd)?


BTW - all 4 prongs are the same size & you cannot swap relays in this circuit to test the fuel pump - it requires both relays (it's a VW, right)

[john70t]

(just noticed they printed the circuit on top. dooh)

Apply 12V+ wire to 86. 85 to negative. That energizes the control circuit field coils.
It should "click" when the magnet pulls in to connect 30 and 87.

Ohm meter leads on 30 and 87. That's load circuit(battery to pump).
Don't short.
It should have zero ohms if the relay is making a connection, and working.

[RWebb]

I was finally able to find the schematic in the (worst bentley ever) bentley. It looks like the control circuit should have +12 V on 85, not on 86, which would get negative. Right? (I think it had a diode in it and would rather not blow that)

[mreid]

I don't see a diode schematic symbol on the relay case. In fact, that relay does not have a diode, so don't worry about burning out the diode. Either pin can have ground, so thats not a factor either. Get a spare relay. They are cheap and in an older car you should have a spare anyway.

[john70t]

My bad. I based polarity on the language:
85 - Output: Actuator (Negative Winding End or Ground)
86 - Start of Winding

The diagram clearly shows the opposite. Good catch.

[aigel]

You are over-analyzing this. There is no diode in there as mreid already told us.

For bench testing you can hook up 85 and 86 to 12 V either way and test resistance across 30 and 87.

The magnetic field created in the relay to pull the switch closed can be either polarity, as it is pulling in a ferromagnetic switch that is "equal opportunity" - attracted to either polarity magnetic field.

G

[RWebb]

Vanagon "people" claim there ARE diodes in these relays

also, what is that little triangle above the "24" in the pic? is it not meant to convey a diode being there?

[john70t]

There may be a diode. Using a thin wire (20 gauge) will limit current when tapping it. It shouldn't require much to activate.
Still, it's just a relay...

I'm a little confused with that diagram:
That nine-legged "spider" (#26 in the middle) should be a common battery/chassis ground leading to "h" on the right.
-The diagram indicates .5W (voltage) there.
-The same .75W is shown before and after the injectors.
-The circuit leg labeled "II Fuel Pump Relay" in the center/right of the picture does not lead to the fuel pump.

The 9/12+Volts which operate the injectors looks to be coming from below(#25), but I thought the Digifant System operated/controlled the fuel-air management.

Damn I wish EarlySMan was still with us.

[speeder]

With an assistant, can you test whether power is going to the relay in either *key on* or *start* position, (whichever it's supposed to be)? You can also jump the fuel pump from the relay plug. Have you already determined that no juice is going to the fuel pump?

This stuff is usually fairly simple w/o even testing the relays individually, but it requires a test light and an assistant. Good luck.

[sjf911]

Originally Posted by john70t

There may be a diode. Using a thin wire (20 gauge) will limit current when tapping it. It shouldn't require much to activate.
Still, it's just a relay...

I'm a little confused with that diagram:
That nine-legged "spider" (#26 in the middle) should be a common battery/chassis ground leading to "h" on the right.
-The diagram indicates .5W (voltage) there.
-The same .75W is shown before and after the injectors.
-The circuit leg labeled "II Fuel Pump Relay" in the center/right of the picture does not lead to the fuel pump.

The 9/12+Volts which operate the injectors looks to be coming from below(#25), but I thought the Digifant System operated/controlled the fuel-air management.

Damn I wish EarlySMan was still with us.

The number is the wire diameter in mm similar to gauge and the letter is the color of the wire. 0.5W is a 0.5mm white colored wire.

Relay II sends power to the fuel injectors, relay I, and the Digifant unit that looks like it then activates the fuel pump by grounding the upper terminal on the first relay (85) probably in response to some signal that the engine is actually running.

[RWebb]

yes, I think that is how it works (based on my extensive reading of Samba posts)

thanks everyone! there is no assistant - I may be able to recruit later but need to limit the recruitments, so will save that for something that absolutely needs 2 people

I think I'll just use a 9 V battery to be safe - if it clicks I know; if no click then I may need more than 9 V.