Gas Heater Relay Voltage

[frogman_94]

I think I traced the issue as to why my gas heater fuel pump is not working. I pulled it out and hooked it up directly to a 12v battery and by tapping one terminal with the positive lead from the battery it does work.

I tested the voltage at the two wires that connect to the fuel pump and I only see 10v. The next spot to check is the wires going to the relay. I have 12v on one side (terminal M) of the relay but only 10v on the other side (terminal J).

Should I be seeing 12v on the output side and does this sound like the relay might be the issue?

The relay is 211 963 141

[mondshine]

Focus on the points at the letter O on your diagram.

If your test light and a 12V+ source are connected to the fan motor's red wire. and the 12V- is connected to the fan motor's brown wire... The fan motor should run.

With the motor running...
The white wire, triggering the coil, is providing a path to ground switched once per revolution of the fan motor.
Touching the probe of your test light to the white wire will make the test light flash at such a rate, that the test light will appear to be constantly lit.

The green wire provides a path to ground to operate the fuel pump. Through a set of nylon gears, the fuel pump points close once per 33 revolutions of the fan motor.
Touching the probe of your test light to the green wire will make the test light flash at a steady rate; a little less than one second apart (IIRC).

Good luck

Edit:
You will notice on your diagram that the green wire from the fan motor is connected to a brown/white wire to the pump.
That's because in DIN wiring standards, a brown wire is a ground, but a brown wire with a white trace is a switched ground.
The green wire to the pump (G6 on your diagram) supplies system voltage to the pump (provided other conditions are met), but it is the switched ground from the points that makes the pump go tick-tick-tick.


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[frogman_94]

The points are working. I tested the leads to the fuel pump with the motor running and I see the light flash. But the voltage at the fuel pump is only 10v.