Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

Bob

On Sunday, April 1, 2018 at 3:33:58 PM UTC-4, Robert11 wrote:
Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

Bob

Probably depends greatly on whether it's a quality switch from a major
supplier or a 10 cent one from Ebay. I would suspect oxidation would
be the problem. Using a cheap alloy would make it more problematic.
They use dip switches of various kinds on circuit boards in furnaces
and similar and I guess they mostly work. Though those switches probably
rarely are moved, to it's a bit different.

On Sun, 1 Apr 2018 12:33:54 -0700 (PDT), Robert11
wrote:

Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

Bob

The contacts oxidize a WEE little bit and the milivolts cannot get
through.

On 4/1/18 2:50 PM, trader_4 wrote:
On Sunday, April 1, 2018 at 3:33:58 PM UTC-4, Robert11 wrote:
Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

Bob

Probably depends greatly on whether it's a quality switch from a major
supplier or a 10 cent one from Ebay. I would suspect oxidation would
be the problem. Using a cheap alloy would make it more problematic.
They use dip switches of various kinds on circuit boards in furnaces
and similar and I guess they mostly work. Though those switches probably
rarely are moved, to it's a bit different.

Is there any reason he couldn't replace it with a regular three
way mercury switch?

On 04/01/2018 05:00 PM, Dean Hoffman wrote:

[snip]

Â*Â*Â*Â*Â* Is there any reason he couldn't replace it with a regular three
way mercury switch?

Mercury is considered a hazardous material?

On 04/01/2018 01:33 PM, Robert11 wrote:
Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

It's a common problem for dry circuits (very little current or voltage
across the contacts). Relays and switches meant for those sort of
applications often have gold plated contacts or are designed with a
wiping action across the contacts.

Are the contacts exposed or is the switch sealed? Back in the day of
backplanes with edge connectors, the Pink Pearl fix was the first thing
to try. Pink Pearl is a name for a Papermate eraser which worked very
well for removing oxidation from the fingers on the circuit board.

On Sun, 1 Apr 2018 19:20:39 -0600, rbowman wrote:

On 04/01/2018 01:33 PM, Robert11 wrote:
Hello,

Just would like opinions on this.

Have a slider switch (typical, small, 2 position kind) on a home furnace
relay box.

Switch position allows for either normal running of the furnace, or, in the event of a power loss,
to operate as a gravity system between the high and low temp. limits of the furnace.
Called a millivolt system.

So, this slider switch, being about 15 years of age now, gets very, very, little use.
Maybe once or so per year.

Just took the relay box apart, and the switch has lost the ability to make electrical contact anymore.

Surprising.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

It's a common problem for dry circuits (very little current or voltage
across the contacts). Relays and switches meant for those sort of
applications often have gold plated contacts or are designed with a
wiping action across the contacts.

Are the contacts exposed or is the switch sealed? Back in the day of
backplanes with edge connectors, the Pink Pearl fix was the first thing
to try. Pink Pearl is a name for a Papermate eraser which worked very
well for removing oxidation from the fingers on the circuit board.


The old-tyme TV tuner cleaner works well - or De-Ox_it. Squirt,
operate the switch 50 times or so and try it.

Is this more or less "typical" for these small slider type switches ?

What actually happens: contacts get oxidized, or...?

It's a common problem for dry circuits (very little current or voltage
across the contacts). Relays and switches meant for those sort of
applications often have gold plated contacts or are designed with a
wiping action across the contacts.

Are the contacts exposed or is the switch sealed? Back in the day of
backplanes with edge connectors, the Pink Pearl fix was the first thing
to try. Pink Pearl is a name for a Papermate eraser which worked very
well for removing oxidation from the fingers on the circuit board.

+1
the problem is due to a combination of the material the contacts are made of and the low voltage and current.

I would replace the switch and just slide the switch once a month to keep it clean as a maintenance item.

mark