Weil McLainl CG-4-SPDN, version? and 'buzzing' relay

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Old 03-14-14, 11:49 AM
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Weil McLainl CG-4-SPDN, version? and 'buzzing' relay

Furnace specifics:
Furnance Weil McLain
model CG-4-SPDN
Series -11 Gas-88K BTU

My first question is: Looking at the above specs, how can I tell if this is a standing pilot or electronic ignition? (also, what is difference between CG and CGa?)

Second question: it appears the relay is buzzing - cycling on/off very quickly. What are some possible causes?

I downloaded the manual but can't figure out the model mapping to begin any trouble shooting.

Assuming a standing pilot, it seems that the only thing the relay controls is the circulation pump?

Thanks for your help

John
 
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Old 03-14-14, 03:30 PM
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how can I tell if this is a standing pilot or electronic ignition?
Is there a standing pilot? In other words, if you look down inside the burner chamber, is there a pilot light lit? Does your gas valve knob have a position on it that says "pilot" ? I believe that the " SP " in the model number indicates Standing Pilot, but not sure...

it seems that the only thing the relay controls is the circulation pump?
No, shouldn't be... there should be TWO poles on the relay, one should control the circulator and the other should send power to the gas valve.

I need to look at your manual.

OK, I'm back, and as usual unable to find the wiring diagram for your boiler in the library.

Tell us more about your system... is it ZONED? (in other words, electric zone valves and more than one thermostat)?
 
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Old 03-14-14, 05:16 PM
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Hello, and thank you for your response. If I could see the furnace, I could answer the questions, but I am trying to help someone long distance, hence I am trying to figure out the configuration just from name plate data....
So, if I could figure out how they compose their nameplate data that would solve the mystery but...no such luck as yet.
I have the wiring diagram...I mis-spoke, sort of...the 2 pole relay controls both the circulation pump and a permissive to the 24vac for the gas valve.
The arrangement is straight forward....single zone, one thermostat (simple Honeywell helical spring that tips a mercury switch capsule).

Some things that would cause the relay to chatter include (I am theorizing here):
1. bad 24 vac xformer - buzzing could be core laminations vibrating due to age...(wish I were there to listen)
2. bad thermostat - weakend helical spring
3. bad relay
4. partial short in 24vac load that is dropping the 24vac down...
5. partially shorted wiring to thermostat....
All of these seem like a real stretch....everything on the furnace is original (circa 1992).
If I were to pick the item with the best chance of being the problem, I'd try the thermostat - 1970 vintage.
Have I overlooked something?

-J
 
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Old 03-17-14, 04:21 PM
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but I am trying to help someone long distance,
Makes it double difficult! third party long distance!

Need to define the noise. BUZZING or CHATTERING. Buzzing as you say could be nothing, but a relay CHATTERING, that is, opening and closing very fast, is definitely something.

1. bad 24 vac xformer - buzzing could be core laminations vibrating due to age...(wish I were there to listen)
Buzzing transformer would not cause relay to chatter.

2. bad thermostat - weakend helical spring
Probably would be my LEAST likely suspect! Especially if it were the type with the bi-metal and mercury bulb. There's just no way those can 'chatter', or buzz.

3. bad relay
If it's CHATTERING, then I would say no, not likely

4. partial short in 24vac load that is dropping the 24vac down...
Even a FULL short, such as in the coil in the gas valve. When relay closes, shorts transformer, relay opens, etc... you know what I mean. This would be my first line of attack.

5. partially shorted wiring to thermostat....
I don't think so. A relay requires more current to PULL IN than to HOLD, so if the thermostat wiring WERE partially shorted, the relay would pull in and HOLD, not chatter. Low enough resistance to pull in would hold.

================

First thing I would do is disconnect the gas valve and call for heat... and/or measure resistance of gas valve coil.

Does the system have a VENT DAMPER?
 
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