Furnace board schematic

[Shagreobe]

hey ya'll, im looking for either a schematic or just a value for a capacitor. See attatched photo...The cap im looking for is C3 on the right side

[R_J]

Re: Furnace board schematic

It is likely similar to C20 Looks like a 104 (0.1µf) maybe 1kv? does not look that critical

[petehall347]

Re: Furnace board schematic

pic here of what it should look like . https://www.amazon.com/White-Rodgers.../dp/B00DS6QM6E
is it in parallel with that diode ?

[stj]

Re: Furnace board schematic

is that MOV (rv2) cracked or is it dirt?

[stj]

Re: Furnace board schematic

It is likely similar to C20 Looks like a 104 (0.1µf) maybe 1kv? does not look that critical

that is only rated for 63 or 100v

[R_J]

Re: Furnace board schematic

Ok 1kv is overkill and not required, looks like the voltage across it is 24v so 63v or 100v would be fine.

Just a note, the board should operate without the C3, so if it doesn't there will be something else wrong

[Shagreobe]

Re: Furnace board schematic

I havent looked hard at the board. just kind of obvious there is a fried cap. 104 gives me a starting place. Maybe I'll have time this weekend (yeah, right) to look at it

Oh, 1KV would cover it i would think

[R_J]

Re: Furnace board schematic

I just suggested the cap voltage before I found a picture of the rear of the board and where it was connected, then found a manual that uses this board so I then knew where it was in the circuit.

[redwire]

Re: Furnace board schematic

In the pic of the blue cap, I see "103" marking on it.
The flame-detect section needs a HV disc capacitor, these are typically 103 at least 100V.
I notice the broken cap C3 is much smaller in size than C23 in other pics of the White-Rodgers PCBBF110.

If the cap is too big and is the flame-detect blocking cap, it would have sluggish response and might false trip on flame out.

[R_J]

Re: Furnace board schematic

C3 connects between J58 pin 6 (also C on terminal strip) and J58 pin5 which is the load side of the fuse. so basically C3 is across the transformer (after the F1 fuse)

[redwire]

Re: Furnace board schematic

Ah I'm wrong then, I followed the trace and see the cap is for noise filtering from the 24VAC transformer. Not a critical part.
In a few eBay pics C3 is smaller than C20, so I thought around 10-33nF which is what I'd use but 100nF works too. At 50-100V I would go with because 24VAC is 35Vpk.

[alfatv]

Re: Furnace board schematic

You never said what's going on. Are you 100% sure the board is bad?

[Shagreobe]

Re: Furnace board schematic

Moot point now...He decided to get a new furnace, so I have a board with a blowd cap. Ill throw it on the spare board pile in case i need a part off of it or something.
Thanks for ya'lls help