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From: John Robertson <jrr@flippers.com>
Newsgroups: sci.electronics.repair
Subject: Re: Robertshaw mechanical thermostat
Date: Wed, 25 Jun 2025 14:31:44 -0700
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On 2025-06-25 8:45 a.m., Fred wrote:
> micky says...
> 
>   > When I thought this was a mercury switch, before I  read
>   > it a second time, I thought it likely a wire to the
>   > swtich had broken where it flexed.  Even good wire could
>   > break after 45 years.  But a reed switch changes the
>   > odds towards a failed switch.
> 
> Thanks very much for the reply.  Yes, my conclusion was that
> while a mercury bulb could last forever, a reed switch is
> going to wear out eventually.  From contact pitting I would
> think, or perhaps an arm would break.
> 
>   > What happens if you use measure the voltage across the
>   > reed swithc when the temp and setting calls for AC. It
>   > should be zero or teeny-weeny if the switch is good.
> 
> I haven't done that yet, but will give it a try if I can get
> the front cover off - it's not clear how that's supposed to
> happen.  Probably just a friction fit.
> 
>   > But I don't remember or never knew if AC starts promptly
>   > when the thermostat tells it to.
> 
> Yes, the blower motor starts immediately when the thermostat
> switches.  I really don't think there's a problem with the
> AC itself.
> 
>   >> Does anyone have a recommendation on a simple
>   >> non-programmable Heat/Cool thermostat?  Or a brand to
>   >> avoid?
> 
>   > FWIW https://www.ebay.com/itm/277091077135  $55 -S&H
>   > after all t hese years
> 
> Yeah, but if I'm going to replace it, I think I'll just get
> a "modern" one at Home Depot for less money.  I don't need
> it to be programmable, but I would like to be able to adjust
> the hysteresis.
> 

I have a variety of Reed Switches for sale for classic arcade games, but 
I expect it would cost less to just replace the thermostat than buying 
and shipping a NOS reed switch...

https://flippers.com/catalog_oc/index.php?route=product/search&search=reed%20switch

John :-#)#

-- 
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