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Wuzzat? 02-01-2013 10:48 AM

Pilot flame sensing switch 6H
If this switch 6H fails to detect the pilot, will the gas supply to the pilot remain on forever because the pick coil is energized, and the gas will be carried away forever by the inducer motor?

The schematic diagrams in these pdf files are just like my furnace in the area of switch 6H.,ss-1so~1.pdf

Wuzzat? 02-02-2013 06:34 PM

The thing finally misbehaved while I was measuring it.
Here's my proposed e-mail to a few well-recommended HVAC companies tonight.

Subject: Request for bid

Dear Sir/Madam:

For a

1982 Bryant Gas Furnace
Model 397HAW060140
Product 397HAW060140 ACBA

the SPDT pilot-flame sensing switch intermittently fails to power the main gas valve coil. Also, it always powers the gas valve pick coil, so the spark module runs the whole time the main burners are on.

The switch seems to be part of the pilot assembly and I don't feel qualified to work on gas piping so I'd like to know if you want to bid on replacing this switch assembly.
If so, I'm hoping you can come out on Monday or Tuesday; I can probably coax it to work that long.
I'm in the xxxx area of xxxx.

I look forward to your reply.

Thank you.


Wuzzat? 02-04-2013 08:50 AM

Problem solved
I found that whacking on the switch with a screwdriver causes the switch to work but not for the reason I thought.
My regular HVAC guy called back and told me that the switch/pilot assembly/ pilot orifice gets clogged with junk, and whacking it clears the orifice, I guess for the foreseeable future. The bimetallic switch is very sensitive to a strong pilot flame.
And the pick valve/spark module always being energized by this SPDT switch is contrary to the Theory of Operation but many furnaces do that(?)

There was one point where the 'stat was supposed to be asking for heat but was telling the furnace to shut off, so I replaced the 'stat - $25 at HD for a backlit Honeywell model. Some of these noname 'stats were going for $9.
I'll use the old 'stat as an interior digital thermometer.

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