MDG9700AWW Maytag gas dryer won't heat up air

shadow2556

Premium Member
Joined
Mar 5, 2009
Messages
15
Location
San Diego, CA
Model Number
MDG9700AWW
Brand
Maytag
Age
More than 10 years
I have a Maytag Neptune MDG9700AWW gas dryer. The machine is about 15 years old. Recently It can't seem to heat up air. The igniter glows red, ignites gas, but the flame quickly subsides. About a minute later, the cycle repeats. The air is not even warm.


What I have done:
1) Air vent was disconnected during the troubleshoot to make sure no blockage.
2) Replaced two gas valve coils.
3) Checked the high limiting thermostat, it was close to 0Ω at room temperature.
4) Checked cycling thermostat, it read around 8KΩ at room temperature. Used a hair dryer to blow hot air to it and the resistance dropped accordingly.

I can't get to the radiant sensor unless I remove the drum. I don't think I am going to replace the gas valve assembly or the control panel. Anything else I should check before going for a new dryer? Thanks!
 

rickgburton

Appliance Tech - Moderator
Staff member
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Jul 11, 2006
Messages
34,775
Location
Murray, Utah 84107, United States
If the dryer is not assembled while you're checking the gas valve and flame the heat from the flame will pile up on the safety t-stat and shut it off almost immediately. That's what it looks like in the video. If I'm wrong and you have good airflow out the vent, Set your meter to measure AC Volts and insert the leads into the back of the two wire connector going to the gas valve. If you have a constant 120 VAC while the flame is going on and off, the problem is with the coils, igniter or flame switch. If your meter leads are too big use this trick:
safety pin 500x250.jpg
 

shadow2556

Premium Member
Joined
Mar 5, 2009
Messages
15
Location
San Diego, CA
Hi, Rick,
I have a total of five wires connecting to the gas valve assembly. Three of them, Blue, White and Yellow, connect to the booster & hold coil; two of them, White and Brown, connect to the secondary coil.

The White wires are connected together. I suppose it is one end of the 110VAC. Where should I probe the other end?
 

shadow2556

Premium Member
Joined
Mar 5, 2009
Messages
15
Location
San Diego, CA
I put my voltage meter across the secondary (white and brown wires).
Not sure where to go from here. I do have good amount of air coming out of the vent. So I don't think the shut-off is activated by a safety thermostat. If there is one, I don't know where it is.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
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Messages
34,775
Location
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shadow2556 said:
I don't think the shut-off is activated by a safety thermostat
rickgburton said:
If you have a constant 120 VAC while the flame is going on and off, the problem is with the coils, igniter or flame switch.
OK, so you have a constant 120 VAC at the connector?
gas valve.jpg

Here's how it works; The igniter is energized through the flame switch. Simultaneously the holding coil and the assist coil are both energized and open valve #1. Both the holding and assist coil are needed to open valve #1. However once it's open the holding coil is strong enough to hold it open by itself. Gas won't flow out until the primary coil is energized to open valve #2
L-split coil C.jpg


The igniter glows red and the heat from the igniter opens the flame switch. When the flame switch opens the neutral side of the assist coil and igniter is lost. The igniter shuts off and L1 now flows through the igniter to the primary coil because electricity takes the path of least resistance.
L-split coil D.jpg


Now both valve 1 and valve 2 are open and gas flows out of the valve and ignited by the still hot igniter.
 

shadow2556

Premium Member
Joined
Mar 5, 2009
Messages
15
Location
San Diego, CA
Rick, thank you so much for the information.

Yours is much easier to understand, especially the schematic. At the moment, I have already dismembered my gas dryer. The Mrs is happy so she can get a new one matching our new washer, however, she does want to keep the stainless drum as a flower pot.

This is (was) my gas valve/burner assembly.

All the connectors are part of the wiring harness.

The harness made troubleshoot very difficult. I think the only device I couldn't get to was the L230-50F thermostat. It was at a hard to reach place and covered by this thick black sticky tar like material.

Now it is in the open, the continuity test is good.

I did have two brand new primary and secondary solenoids installed at the time, so I am guessing my problem had to be the gas valve itself.

Anyway, thanks again.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
34,775
Location
Murray, Utah 84107, United States
That machine has had a lot of work done on it. For one that green tape is not factory so it looks like it's been rewired. Did you buy it used?
 

shadow2556

Premium Member
Joined
Mar 5, 2009
Messages
15
Location
San Diego, CA
Rick, both washer and dryer came with the house two years ago. The Maytag Neptune washer broke down about six months ago. We had to get a new one because Maytag no longer makes parts for that model. The problem was with the controller board, according to the repair guy.
 
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