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Date:         Fri, 10 Aug 2007 21:30:42 -0700
Reply-To:     Mark Drillock <drillock@EARTHLINK.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Drillock <drillock@EARTHLINK.NET>
Subject:      Re: Dometic woes
In-Reply-To:  <E32702F5-0B49-4B4D-BDA2-1753DAC27F49@mac.com>
Content-Type: text/plain; charset=us-ascii; format=flowed

A couple of corrections are in order. The electric heating elements are nowhere near the thermocouple and can't touch it. The flame led sometimes comes on during electric operation for another reason. The thermocouple puts out a very small voltage that is sent on a wire to the led circuit board. The circuit board has a sensitive amplifier that boosts the small voltage enough to turn on the flame led. The sensitive amplifier can also sometimes pickup a false signal coming from the electrical operation.

The button you hold in during lighting does not add extra propane. It turns on the gas, entirely. No button, no gas. The button opens a valve in the propane line. This button/valve has a small return spring that wants to turn the gas back off when you stop pushing in on the button. This is where the thermocouple comes in. There is a small electromagnet that pulls the button/valve in against the spring, but only when the thermocouple is hot enough to send a small voltage to to it. If the flame goes out, the thermocouple stops sending the small electric voltage and the electromagnet stops fighting the spring so the gas valve turns off. It is called a safety valve. No electricity from a hot thermocouple and the return spring will turn the gas off every time. That is why you have to hold the button in a little while, until the thermocouple gets hot. Let go too soon and the thermocouple won't be sending enough voltage to the electromagnet and the spring will turn off all the gas to the burner. Yes, the thermocouple can get weak or stop working and then the fridge will not stay lit.

Mark

Kim Brennan wrote:

> Here's the low down functionality on the Dometic fridge. > > The thermocouple is activated by heat. Normally, this heat is the > propane flame. If one of the other elements (AC or DC...usually DC) > is touching, the light may turn on. Most of the time, you'll know, > and hence this is not a problem. When propane is running the flame > can vary, and this will cause the LED to change in intensity. > > Now about that pump. The basic idea of the pump is to get oxygen to > the combustion chamber when the fridge isn't self drawing. You don't > need to pump vigorously. I almost don't ever pump. But my fridge > draws extremely well. > > How to you get your fridge drawing air from outside properly? When > first starting up the fridge, there is a button you hold down. This > adds extra propane to the combustion chamber. The basic idea here is. > Heat up the flue. As the flue heats up with burnt propane, it will > draw in air from outside via the intake. When things are working > correctly, this won't take very long. 2 minutes at tops, unless you > are in a very hot climate (but then your fridge might have troubles > anyway above 95F.) > > If your fridge isn't working correctly. It is time to service it. > This is not a complicated process. The biggest issue is pulling the > fridge. Once you have done so, the "service" is going to be on > cleaning the nozzle in the combustion chamber and cleaning out the > ash that has accumulated there. > > Some folks have used acid to clean the nozzle. I don't care for that > myself. I used a fine copper wire. > > On Aug 10, 2007, at 10:11 PM, Paul Chubbuck wrote: > >> My indicator light turns bright green right away when the flame >> lights. Is >> that an indication that the thermocouple is, in fact, working and >> properly >> aligned, or is it more complicated than that? >> >> Paul >> >> -----Original Message----- >> From: alfred bagdan [mailto:abagdan@shaw.ca] >> Sent: Friday, August 10, 2007 7:28 PM >> To: paul@takingflight.net >> Subject: Re: Dometic woes >> >> If you have a voltmeter, you could check the millivolts the >> thermocouple >> produces. When they get old they produce less. People who service >> furnaces >> >> replace them a lot. >> I'm not sure what the specs are, perhaps that can be looked up. >> >> Alfred > >


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