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frogman_94 Samba Member
Joined: March 10, 2006 Posts: 118
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Posted: Fri Mar 29, 2024 2:30 pm Post subject: Gas Heater Relay Voltage |
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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
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mondshine Samba Member
Joined: October 27, 2006 Posts: 2776 Location: The World's Motor Capital
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Posted: Fri Mar 29, 2024 4:47 pm Post subject: Re: Gas Heater Relay Voltage |
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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 Samba Member
Joined: March 10, 2006 Posts: 118
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Posted: Sat Mar 30, 2024 10:50 am Post subject: Re: Gas Heater Relay Voltage |
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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. |
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[email protected] Samba Member
Joined: February 21, 2003 Posts: 869 Location: Clifton Park NY Saratoga County
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mondshine Samba Member
Joined: October 27, 2006 Posts: 2776 Location: The World's Motor Capital
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Posted: Wed May 01, 2024 5:51 am Post subject: Re: Gas Heater Relay Voltage |
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Do you know how to perform a "voltage drop test"?
It is a very useful technique for diagnosing problems with a 50 year old electrical system. Read up on it.
It seems that you already suspect a voltage drop across the relay contacts.
When the relay is triggered, (with system voltage at Terminal A) what voltage do you read between Terminal J of the relay and Terminal M of the relay?
What about between Terminal B of the relay and Terminal M?
Here, if you read more than a volt, you have found the problem; a voltage drop due to dirty or corroded relay contacts. Oh, and by the way, voltage drop testing only works with the circuit "live".
Any digital multimeter, from the cheapest Harbor Freight giveaway to a Fluke 87 can do this test.
If you want to confirm these results, place a temporary jumper wire between Terminal M and Terminal J, or between Terminal M and Terminal B.
If the heater works normally, the relay is bad. If not, look elsewhere.
If you are in a "surgical" mood, you can take the cover off of the relay and check the contacts yourself.
This is not a standard automotive relay, it is a so-called "dual 87" relay, because it has two distinct output contacts, which are energized simultaneously. They are a little bit rare, but not unobtainable.
Just an example:
https://www.rallylights.com/hella-hl87483-mini-relay-12v-40a-spst-dual-87-pin.html
It would be wired like this:
Good luck. |
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