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Author Topic: LG gas dryer wont heat  (Read 25634 times)

Offline berniet

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LG gas dryer wont heat
« on: December 26, 2007, 11:33:35 AM »

Hi I am formerly Thomas68  I had troubles logging in.

My LG DLG3788W Gas Dryer is tumbling...ignitor glowing...but no flame is being produced....

i have the front cover off and top off... i have the contol board hooked up... I have bypassed the door switch to get the dryer to work...It is in the condition above for live testing...

Question 1
Do I need the door on to cause air flow over the ignitor Assembly to have the gas air mixture to flow? ???
2
does the Hi limit themistat limit the voltage going to the coils on the ignitor?

When I am doing a test in its present state Should I probe the coil connector attached to the coil or not attached to the coil? ???

3 Should I measure accross the 2 wire connector going wire to wire...or should I probe wire to chasis ground?? when testing for voltage at the coil..

Any help is wonderful

Offline RegUS_PatOff

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Re: LG gas dryer wont heat
« Reply #1 on: December 26, 2007, 01:08:47 PM »
did you do the "GAS Valve test" on page 27 of the service manual ?

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Offline rickgburton

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Re: LG gas dryer wont heat
« Reply #2 on: December 27, 2007, 02:46:40 AM »
OK, the igniter (Glow coil) comes on . Does it turn off? Can you hear a "click" sound coming from the gas valve when you first turn it on? Remove a wire from each component before you test it. You're only looking for continuity for now. You want a reading of 0.0 on each component.
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Offline accapp

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Re: LG gas dryer wont heat
« Reply #3 on: December 28, 2007, 02:08:54 AM »
The door need not be installed for the gas valve to operate, it will shut off once the burner tube high-limit gets too hot. The LG operates differently from any other gas dryer I have encountered, the high limit will shut off power to the ignitor/flame sensor. There does not apear top be any direct connection between the ignitor/flame sensor and the gas valve coils which receive ~90 vdc from the control board to operate them. To test the control board, pull the two harness plugs off the gas valve and see if they are getting the correct dc voltage whn they should. The most important test is still gas valve coil continuity, it should be ~1180 ohms. Most LG gas dryers I work on need a new gas valve.
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Offline berniet

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Re: LG gas dryer wont heat
« Reply #4 on: December 28, 2007, 09:19:58 AM »
It does come on an Glow for a little bit and then it shuts off.
Is the Thermistat high limit the one located in the plastic squirrel cage assembly,  The Thermister is right next to it???I only get about 30-40 volts to the valve assembly.

I am using the diagnostic on that page and really do not know where the Thermistat Hi limit is for step 2

Offline berniet

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Re: LG gas dryer wont heat
« Reply #5 on: December 28, 2007, 09:28:55 AM »
Dlg diag for valves

Offline RegUS_PatOff

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Re: LG gas dryer wont heat
« Reply #6 on: December 28, 2007, 12:09:21 PM »
It's one of these (2) wired in series on the duct

one of them MAY have MANUAL reset button

the other one is automatic reset

as shown on page 16 of the service manual

M220  6931EL3004B 

M230  6931EL3003C

« Last Edit: December 28, 2007, 12:24:40 PM by RegUS_PatOff »
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Offline berniet

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Re: LG gas dryer wont heat
« Reply #7 on: December 28, 2007, 02:48:53 PM »
Here is the Schematic of the dryer.    where should I begin

Offline accapp

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Re: LG gas dryer wont heat
« Reply #8 on: December 28, 2007, 03:41:51 PM »
Do you have the meter set for DC volts when you are live testing? Are you measuring between both leads to each coil and not to ground? What is the resistance of each coil?
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Offline berniet

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Re: LG gas dryer wont heat
« Reply #9 on: December 28, 2007, 08:54:43 PM »
Acapp
I am unplugging the coil and testing in the plug....I am hoping this is correct..I get around 32 volts on the test....Per the manual that I am taking these measurments in AC...

the coils are ohming out to about 1700


Offline accapp

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Re: LG gas dryer wont heat
« Reply #10 on: December 29, 2007, 12:19:35 AM »
Gas valve gets DC power, test voltage with meter set for DC volts. Yes, test between wires on each plug.
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Offline berniet

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Re: LG gas dryer wont heat
« Reply #11 on: December 30, 2007, 08:47:00 AM »
I tested the coils  for resistance 1845    and 1855

the 2 thermostats at the flame funnel tested ok
outlet themostat at the hamster cage assembly tests ok
Flame detect tests continuity

Thermister and moisture sensor test ok

I think that my control board is defective
would there be any way that an appliance repair store be able to check the board itself?

Schematic attached

Offline JWWebster

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Re: LG gas dryer wont heat
« Reply #12 on: February 13, 2008, 08:32:12 PM »
these guys cannot be checked with a meter and they ain't but 20 bucks . replace these dudes. send me a pic of the gas valve assembly dude.
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Offline RegUS_PatOff

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Re: LG gas dryer wont heat
« Reply #13 on: February 13, 2008, 08:46:47 PM »
correction:[/[/b]b]
in some LG dryer manuals, they mention that the Gas Valve Coils use 90v - 120v AC and also mention 90v - 120v DC



LG Gas Valve Coil Assembly Part # 5221EL2002A
« Last Edit: July 15, 2008, 02:26:42 AM by RegUS_PatOff »
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Offline JWWebster

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Re: LG gas dryer wont heat
« Reply #14 on: February 14, 2008, 02:11:24 PM »
I tryed looking up LG online but I coud not find anything like that or any info either. Iso the dude uses DC voltage to operate the coils? That means the controlpanel must also be a stepdown transformer and the is what powers them coils. Oh Brother! That goes back to either no an open coil on the operator (You Pictured) or no dc voltage coming from the main computer board. What a messy way to make a dryer. I do not know a thang about these new fangled LG products but I am learning. Thanks! :2funny: Let me run this one by you then with the dryer running and the glow bar going when it shuts down if I have my fluke meter on the wires coming from the board I should get 90 vdc or around there and would know if the board is powering the coils right?
« Last Edit: February 14, 2008, 02:17:47 PM by JWWebster »
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Offline JWWebster

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Re: LG gas dryer wont heat
« Reply #15 on: February 14, 2008, 02:22:34 PM »
On this dryer the sensor must send signal to the board that ignition has occured and then 90 vdc is sent to the gas valve right? So if his ignitor is firing up that means he has power coming from some relay somewhere other than the control panel. Therefore the  the control thermistat must be some sort of thermister connected to the main board. Are the coils remvable on the gas valve or do you have to replace the whole gas carrying assembly?
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Offline RegUS_PatOff

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Re: LG gas dryer wont heat
« Reply #16 on: February 14, 2008, 03:56:13 PM »
yes, transformer on control board

(120v AC) ignitor is controller by main board & flame detector & limit thermostats

gas valve is controlled by main board (90v DC)

I'm not sure about the separate coils (I'll check later)

LG Service Manuals




« Last Edit: February 14, 2008, 03:58:36 PM by RegUS_PatOff »
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Offline BillR625

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Re: LG gas dryer wont heat
« Reply #17 on: December 03, 2014, 12:15:07 AM »
Just so you are aware that when the Radiant Sensor or what I generically call the flame sensor, when that opens it directs 120VAC to the control board, this is how the board knows the ignitor is glowing and is hot enough to ignite the gas,  and using a transformer and a bridge rectifier it drops 120VAC down to 90VDC for the coils to use..   The flame sensor or radiant sensor is nothing other then a safety, the glow bar has to get hot enough to light the gas. The sensor detects the heat and diverts the current to the control board for the gas valve.. Some dyers have a parallel circuit that when the sensor opens it forces current to the gas valves, the amp draw has to be strong enough to operate the coils to open the gas valve.. Depending on the style of ignitor, some operate as low as 2.8 amps while others aew up around 4 amps... They don't want gas pumping into the plenum without sufficient heat to ignite the fumes. So the radiant sensor was added as a safety, nothing else... This tell the gas valve its safe to open in layman's terms...  Imagine 30 or more seconds of gas pumping out of the gas valve as the ignitor is heating up, when it reached a sufficient temp to ignite the fumes, you could have a small explosion on your hands... Strictly a safety...and opening the radiant sensor also kills power to the glow ignitor so it doesn't remain lit...
« Last Edit: December 03, 2014, 12:18:46 AM by BillR625 »