3 edits |
to mackey
Re: [HVAC] Electric Furnace Not HeatingEDIT* mackey your diagram with the picture and the voltage, your making it a bit confusing, he SHOULD be seeing 240 at every single point, Not 0, he would see 0 if the switch was bad or burned out, although your wording says it, the picture does not, it seems like it indicates it should be at 0 via the switches, that would only be case if one was broken |
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 mackey
Premium Member
join:2007-08-20 |
mackey
Premium Member
2015-Jan-10 2:04 pm
said by LittleBill:EDIT* mackey your diagram with the picture and the voltage, your making it a bit confusing, he SHOULD be seeing 240 at every single point, Not 0, he would see 0 if the switch was bad or burned out, although your wording says it, the picture does not, it seems like it indicates it should be at 0 via the switches, that would only be case if one was broken No, if a switch or fuse was open/burned then he would get 240v across it. If it's good (not open) then it should be 0v or really close to it (it acts like a length of wire). |
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 SparkChaser
Premium Member
join:2000-06-06
Downingtown, PA |
to LittleBill
He's reading across the fuse and over temp that's why it's 0V
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to mackey
maybe we are troubleshooting this different, but if you start on one side circuit, and test every single point from the other side, and the unit is calling for heat, he should be seeing 240 at every single point up to and including the element, how else would the element energize? |
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| LittleBill |
to SparkChaser
said by SparkChaser:He's reading across the fuse and over temp that's why it's 0V shouldn't be 0 if the circuit is energized and calling for heat. should be 240 across the entire path |
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mackey
Premium Member
join:2007-08-20 |
to LittleBill
said by LittleBill: and test every single point from the other side Why do you want to almost double the number of points you need to test? You can check each heater for every possible failure with 4 measurements if you test across the fuses/switches. If you took every measurement "from the other side" then you need 6, not to mention it can be harder to keep the probe tips in place if they're a good distance apart. |
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explain your testing process, short of continuity checks on the switches, i am failing this "0v" test.
if you just test right at the switch itself and you are only doing a voltage check on both sides. regardless of the switch being shorted or open, you would see 240.
i don't see the point of this test, nor do i see how you would see 0. maybe im being stupid, but i have never seen this 0v test before |
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SparkChaser
Premium Member
join:2000-06-06
Downingtown, PA |
It's 0 volts because it's across 0 ohms
If it's not 0 then it's bad. |
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mackey
Premium Member
join:2007-08-20 |
to LittleBill
said by LittleBill:short of continuity checks on the switches, i am failing this "0v" test. You're measuring it like you're doing a continuity check, but as it's still in the circuit and the circuit's powered up you're measuring voltage instead of resistance. If you pulled it out and measured the resistance and got 0 ohms (it's good), when you put it back in the circuit and measure the voltage drop across it you get 0 volts. If you pulled it out and measured the resistance and got infinity (it's blown/bad), when you put it back in the circuit and measure the voltage drop across it you get the full circuit voltage (240v in this case). |
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 Tursiops_GTechnoid
MVM
join:2002-02-06
Brooksville, FL |
Actually, there should be *nearly* 240 Volts across the element terminals...
If you get absolutely ZERO volts across the element (provided that the 240V supply is indeed present), you would have a DEAD SHORT, and the Fuse/Breaker would blow... |
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to mackey
said by mackey:said by LittleBill:short of continuity checks on the switches, i am failing this "0v" test. You're measuring it like you're doing a continuity check, but as it's still in the circuit and the circuit's powered up you're measuring voltage instead of resistance. If you pulled it out and measured the resistance and got 0 ohms (it's good), when you put it back in the circuit and measure the voltage drop across it you get 0 volts. If you pulled it out and measured the resistance and got infinity (it's blown/bad), when you put it back in the circuit and measure the voltage drop across it you get the full circuit voltage (240v in this case). now im starting to think this is a bit of a play on words? 0v meaning 0 voltage drop? yes that makes sense but thats a hell of a way to say it. maybe your just saying it in a very confusing way to me, but if you have 240 + or - 2 or 3 volts, the circuit is good, and not shorted. i am not sure why we are concerned what the voltage drop is anyway, not like we have a reference point anyway. i would check for voltage at the element itself, then in the case of it staying energized i would use a clamp on to see if its pulling amps. to be honest im still not really sure of your testing? your simply looking for a voltage difference on both sides of the switch? |
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mackey
Premium Member
join:2007-08-20
1 edit |
to Tursiops_G
said by Tursiops_G:Actually, there should be *nearly* 240 Volts across the element terminals... I'm still talking about the fuses/switches, not the elements... |
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| mackey |
to LittleBill
said by LittleBill:now im starting to think this is a bit of a play on words? 0v meaning 0 voltage drop? yes that makes sense but thats a hell of a way to say it. Yes, 0v drop across the switches/fuses. I'm not sure what you mean by "a hell of a way to say it," when you put the meter on it it reads... "0 volts" |
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if your testing the switch, lets say the limit switch, and your just testing both sides of the switch, and the circuit is energized, and everything else in the circuit is good. you would see 240V on the meter Regardless of whether or not the switch is good or bad as you technically have bypassed it, testing it that way |
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mackey
Premium Member
join:2007-08-20 |
mackey
Premium Member
2015-Jan-10 2:54 pm
said by LittleBill:you would see 240V on the meter Regardless of whether or not the switch is good or bad as you technically have bypassed it, testing it that way What? No. You would see 0v (drop) if it was good or 240v (drop) if it was bad. You don't have anything bypassed when measuring voltage like that... |
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Tursiops_GTechnoid
MVM
join:2002-02-06
Brooksville, FL ARRIS TM1602
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to mackey
said by mackey:I'm still talking about the fuses/switches, not the elements... Ah, You are indeed correct... My bad.  Sort of reminds me of the story where someone rejected an entire batch of new Fuses because they were "shorted"...  |
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to mackey
said by mackey:said by LittleBill:you would see 240V on the meter Regardless of whether or not the switch is good or bad as you technically have bypassed it, testing it that way What? No. You would see 0v (drop) if it was good or 240v (drop) if it was bad. You don't have anything bypassed when measuring voltage like that... i think im going to wire this up in a test with a light switch and a light bulb. im not sure i agree with you |
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SparkChaser
Premium Member
join:2000-06-06
Downingtown, PA |
said by LittleBill:i think im going to wire this up in a test with a light switch and a light bulb. im not sure i agree with you Take a light switch and measure across the switch. When the switch is on there is 0V across the switch. When the switch is off there is 120V across the switch. (assuming there is a lamp on the switch  ) |
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Yes, now I understand it. I have never tested that way before. And I was thinking about it for a bit. Outside of testing the switch itself. It's a very limited test. It doesn't test the wiring or the connectors. It also allows for a false positive. It also doesn't tell you which side of the circuit is bad.
An example in this scenario would be a failed fusable link and failed limit switch. Just utilizing this test would indicate that the limit switch is good when in fact it's the lack of voltage on the circuit masking the limit switch failure.
All though there is a couple ways to test another way to test would to ground one side and reference 120v.
To each their own
My question on the 0 volt test. How much resistence do you need in the circuit to show 240. I am assuming that is the only difference. |
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