Author Topic: Cold control thermostats and switches in appliance circuits  (Read 5808 times)

Offline thepunk

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Cold control thermostats and switches in appliance circuits
« on: December 11, 2008, 01:28:39 PM »
My question applies to most appliances.  When doing voltage tests on switches, thermostats and cold controls in refrigerators, can you test voltage across the switch contacts.  I have been checking out some information about circuit testing and some info indicates that you can test a switch in a series circuit, such as a cold control and if it is closed you will get a reading of 0 volts, if it is open you will get a reading of 120 volts.  A voltmeter in series with a switch!!  I always thought you measured voltage from one side of the contact to common on the other side of the line closer to the negative side of line out.  If a voltmeter is in series with the contacts of the switch, thermostat or control, how can it get a reading, unless the voltmeter acts as an amp meter, or maybe the voltmeter just takes the path of least resistance, can anyone explain this.

Offline whirlpooltech

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Re: Cold control thermostats and switches in appliance circuits
« Reply #1 on: December 11, 2008, 01:41:44 PM »
Quote
If a voltmeter is in series with the contacts of the switch, thermostat or control, how can it get a reading, unless the voltmeter acts as an amp meter, or maybe the voltmeter just takes the path of least resistance, can anyone explain this.

When your taking a voltage reading across the contact of a switch your meter is in parallel with the switch, not in series.

So when the switch is closed you do not get a voltage reading because the probes of your meter are on the same line.


Offline whirlpooltech

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Re: Cold control thermostats and switches in appliance circuits
« Reply #2 on: December 11, 2008, 01:43:56 PM »
Here are some self study manuals that you may also find helpful.

http://appliancejunk.com/forums/index.php?action=downloads;cat=23

Offline thepunk

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Re: Cold control thermostats and switches in appliance circuits
« Reply #3 on: December 11, 2008, 08:30:19 PM »
I never thought of the meter being in paralel with the switch, but I haven't done a lot of voltage tests, mostly amp and ohms.  that is really helpfull, Thanks!  I tried to access your link about diagnosing appliances, but the link takes me to a hacks page, is there a missing link somewhere.  Thanks for info.

Offline AJ

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Re: Cold control thermostats and switches in appliance circuits
« Reply #4 on: December 11, 2008, 08:38:00 PM »
Link works ok for me.

You can also go to the "Helpful Links" box on the left side.
Click on "Manual Index" and then towards the bottom of the "Downloads" page you will see the "Self Study Appliance Repair Manuals" link.

Hope you find our website helpful.

Offline RegUS_PatOff

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Re: Cold control thermostats and switches in appliance circuits
« Reply #5 on: December 11, 2008, 09:40:07 PM »
... can you test voltage across the switch contacts. 
I have been checking out some information about circuit testing and some info indicates that you can test a switch in a series circuit   ...

.... if it is closed you will get a reading of 0 volts, if it is open you will get a reading of 120 volts.... 

the switch is in the series circuit, not your voltmeter.

yes, if the switch is closed, you'll read 0v, and if it's open = 120v
(unless it's in an electronic circuit, then it may have any voltage across it,
even a DC voltage)
« Last Edit: December 11, 2008, 09:46:47 PM by RegUS_PatOff »
After leaving this Earth, "Do you want the smoking or non-smoking section?"

Offline JWWebster

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Re: Cold control thermostats and switches in appliance circuits
« Reply #6 on: December 11, 2008, 09:42:58 PM »
If AJ gives you a link open it first..when opened it usually leads to the download of the manual. This tells you the size of the manual and how many folks have downloaded it. Instead of "save link as" you open the link and then that goes to the link to want to "save link as". Are we clear on that? Haha :D
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Offline thepunk

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Re: Cold control thermostats and switches in appliance circuits
« Reply #7 on: December 12, 2008, 06:39:57 PM »
Thanks, I'll check out the link.  Yea it finally clicked in my head.  Meter in paralel with switch, makes since. I mean if you have a resistor in paralel with a switch in series with a circuit and most voltage is passing through the resistor after you open the switch, why wouldn't the meter also have voltage going through it after the switch is open. I was explaining it to a friend at work and he said, I see, Oh Yea.  He use to do refrigeration work, and it took him a while to get it to.  Thanks again!

Offline JWWebster

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Re: Cold control thermostats and switches in appliance circuits
« Reply #8 on: December 12, 2008, 07:44:30 PM »
Naturally if the switch is thrown no electrical voltage is gonna show up because you are only getting one side of the circuit. To get a voltage reading you must have a line L-1 and neutral to feed back to. If the switch is bad or OPEN then one side of it will be L-1 and the other side will act as a neutral feed.
May the hinges of our friendship
        never grow rusty.

About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
I love fan letters! LOL

Offline thepunk

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Re: Cold control thermostats and switches in appliance circuits
« Reply #9 on: December 14, 2008, 02:39:08 AM »
What do you mean by a thrown switch.

 

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