LG Gas Dryer DLGX7601WE - No Heat

[blaqkatom]

5.5 year old LG DLGX7601WE gas dryer suddenly stopped heating. After some period of time, control panel would light up with “GAS” text and no other errors. After taking apart and running on timed cycle, I can see the igniter glow, but I can never smell/see gas, get that audible click from the valves, or ignition.

After opening the thing, I noticed a good amount of corrosion on the outside of the drum, and on the sides/floor. Looking at all of the internal components, the motor looks perfect, and even the gas valves look unscathed. There is slight discoloration on the plastic of the valve 1 connector and a small I can recall putting a way too wet load into the dryer at one time thinking it shouldn’t have been a problem. I won’t be doing that again.

• Verified gas supply is working and line is good.
• Verified zero resistance on blower thermostat, hi limit thermostat, outlet thermostat, and flame detect.
• Verified correct resistance on igniter AND it glows properly during cycle.
• Verified correct terminal resistance on both gas valves.

I ran a timed cycle with my multimeter probes on the valve 1 connector and saw little to no DC voltage. I repeated this on the valve 2 connector (waiting 10 sec after igniter off) and saw the same thing.

I found the service manual for the dryer and it appears the motor controls the gas valves? With the unit off/disconnected, I checked resistance of the terminals marked for the Motor, am getting 1.6ohms (under the 2-3ohm expectation in the manual). I checked resistance of the terminals marked for the Gas Valve, and am getting an Open Loop. Is this it? Am I dealing with a bad motor? Or are there additional tests I need to be doing here? For good measure, I took a look at the control pcb and see zero burn marks, and everything looks good.

https://imgur.com/a/1QGZ3T1

[Vance R]

2 hours ago, blaqkatom said:

I found the service manual for the dryer and it appears the motor controls the gas valves?

The motor switch is a safety switch - the motor has to be running to complete the circuit for the gas valves. The 90 vdc is controlled by the board.  The service manual is show the same wire diagram for both electric and gas units. Unfortunately it is the diagram for the electric dryer. Here is a wire diagram for a similar dryer. The igniter will only glow when the board turns it on and the motor has to be running. There should be 90 vdc on valve 1 (sv1).  When the flame sensor opens the igniter should go out and valve 2 (sv2) should get 90 vdc to start the burner. 

 

Since this for a different model the wire colors could be different. 

[Madison]

Did you checked flame sensor? I meant voltage 

Edited January 14 by Madison
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[blaqkatom]

On 1/13/2024 at 8:38 PM, Vance R said:

The motor switch is a safety switch - the motor has to be running to complete the circuit for the gas valves. The 90 vdc is controlled by the board.  The service manual is show the same wire diagram for both electric and gas units. Unfortunately it is the diagram for the electric dryer. Here is a wire diagram for a similar dryer. The igniter will only glow when the board turns it on and the motor has to be running. There should be 90 vdc on valve 1 (sv1).  When the flame sensor opens the igniter should go out and valve 2 (sv2) should get 90 vdc to start the burner. 

 

Since this for a different model the wire colors could be different. 

Getting little voltage across DC or AC. I have tried putting probes in the connector for Valve 1, and even run and waited 20 seconds after the igniter glows on the Valve 2 connector. Could I be testing something wrong? I do note I see a jump from zero to some voltage when I hit the power button for the unit. I’m just jamming my round probes into the wires where the flat tabs from the valves would go. I’ve never seen flat probes and alligator probes wouldn’t be proper.

I’ve paid close attention to the motor and can see the centrifugal switch is working right. This all has to be a controller board, no?

[blaqkatom]

On 1/14/2024 at 8:48 AM, Madison said:

Did you checked flame sensor? I meant voltage 

So I went back to test the flame sensor and was able to get really wonky readings consistently. Ordered a new flame sensor and verified it tested fine. I installed and unfortunately same issue.

[Vance R]

If possible may want to check for voltages at the board.  Valve coil 1 should get 90 vdc when the igniter comes on, valve coil 2 should get 90 vdc when the flame sensor opens and the igniter goes out