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A few thoughts (astoundingly long) Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 22 Aug 2007 10:40:05
In Reply to: Follow-Up, can't find problem., Wil W [Profile/Gallery]
, Tue, 21 Aug 2007 20:11:58
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First, if it's an electric dryer, it probably runs on 220. Make sure both of the (electrically) hot leads are hot (powered) at the outlet. The motor may run on only 110; the heater uses both.
Continuity is a strange thing - how much is enough? If the heater coil measures as continuity, that's a good sign - probably not burned out. But not so with switches.
If a switch has only .5 ohm of resistance when cold (room temperature), it'll drop 12 volts across it when you hook it up to the normal dryer load (typically 25 amps per leg). That won't keep the heating element from getting hot. But the math says that the switch contacts are seeing about 125 watts - in a small space, those switch contacts are going to get hot FAST. When they get hot, the resistance increases (FAST). So the resistance increases in the contacts - more power in the contacts, which means it gets hotter, which means more resistance... Eventually, the resistance of the switch contacts is so great that minimal power is running into the heater coil. No fuse is going to blow because you aren't pulling too much current - in fact, with the high switch resistance, you're pulling very little.
This happens a lot in car troubleshooting. The windshield washer motor doesn't run. You unplug the motor, stick in your meter, and you read 12 volts when the squirter switch is pulled. Plug in the motor, and it doesn't run. Must be the motor, right? But if you measure the voltage on the motor when it is plugged in and you pull the squirter switch, you'll see only 1 or 2 volts across it - not enough for the motor to run. Why? A bad contact at the squirter switch. But since the meter alone (no motor) pulls (almost) no current, the resistance of the switch contact doesn't matter. No current, no voltage drop across the switch contacts.
Most consumer meters don't measure below a couple of ohms well. 1 ohm or .1 ohm will look pretty much the same. But when you're talking about big amps, that's a lot. For precision low resistance measurements, it takes special meters.
So, how does this impact your dryer? It depends on how experienced you are working on circuits. With the schematic, and the power ON, you can trace the voltage, and see where it 'goes away'. CAPS INTENTIONAL - 220 VOLTS IS LETHAL SO DON'T MESS WITH IT UNLESS YOU KNOW WHAT YOU'RE DOING - AND EVEN THEN, BE ULTRA CAREFUL. Whew, sorry for shouting. Troubleshooting a live circuit can show up these bad connections, but it is best left to an expert.
Basically, it can be hard to troubleshoot a bad switch contact without the right equipment. All switches should read as low as your meter will go - pretty much the same resistance as when you touch the leads together. If any switch looks like it may be a little more than the others, suspect it.
I know folks talk about repair vs. replace. Let's put it this way - I just dropped a new transmission into my washer (about 6 years old). For $150, I got it running again, versus spending $500 or more for a new one. It would have cost me $250 at least (parts included) for a serviceman. If the washer were 12 years old, I'd think of replacing it with new.
And an oh by the way. This is the second washer tranny I've done. The first one was on a washer that was at least 15 years old when it died. The tranny was all metal, and the innards chewed themselves into filings. The replace tranny was still going strong ten years later when I junked the washer. On the new machine, access to the tranny was cake - 10 minutes versus the 45 minutes of the old one. I pulled apart the bad tranny - all plastic gears (!), and death due to a plastic tang breaking off. So that 'new' tranny I put in will have about the same lifespan. Yes, they don't make them like they used to - easier to service, but you need to service them more.
posted by 192.249....
, Tue, 21 Aug 2007 07:55:28, Tue, 21 Aug 2007 20:11:58, Wed, 22 Aug 2007 10:40:05 <-- Viewing This Message
, Wed, 22 Aug 2007 10:08:20
, Tue, 21 Aug 2007 09:06:38, Tue, 21 Aug 2007 10:06:35, Tue, 21 Aug 2007 10:22:55
, Wed, 22 Aug 2007 09:19:06
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