Whirlpool WED72HEDW1 Intermittent motor spin

[griinder]

I have a Whirlpool duet dryer that stopped tumbling. No error codes. I hear a relay click and motor makes a thud. The drum turns maybe a half inch then just stops. No humming or grinding. I took the belt off the pulley and turned it on once or twice and the motor did the same thing. I disassembled it to investigate further. I cleaned up the rollers, and the belt appears to have tension. I do not see a belt switch. I metered the thermistor (rectangle sensor) and it had continuity. I also metered resistance across the thermal shut off and read around 10k. I pulled the motor out and and bench tested it by applying 110v to pins 4 and 5 and the motor seemed to spin up nice. I only did this once.
The vent was pretty packed with lint, so I figured I'd reassemble and try again. Unfortunately I got the same result. I did then toggle the start button 15-20 times after reassembly. During those 15-20 times it did spin up the motor and drum twice during that. I assume I should check for consistent power at pins 4&5 of the harness next. Both when it spins the motor and doesn't.  Which relays should I check? If I do have consistent power at the harness when the motor doesn't spin, is it the motor? If I don't have consistent power where should I look next? I suppose I should also bench test the motor a few more times. Maybe the one time I bench tested it was one of the "lucky" starts. Looking for more direction and suggestions.

[griinder]

I fixed it. There was power at the harness when it would run, and no power when it wouldn't. I traced power back through thermistor and door switch to the control board. There is a lead from the blue relay that traces over to the blue wire on the 2 wire receptacle that houses the blue and black wire. It is right behind the blue relay in this picture. That lead was a cracked/burnt lead on the blue relay. I resoldered and it now works every time.

[AJ]

Good job!!
Thanks for the update

[archibald tuttle]

good logical work. i'm not sure circuit boards have really helped the operation of simple appliances like dryers. previously relays would have been a little larger and contacts distinct and called out in wiring diagrams and thus it would have made this easier to test, although you were able to observe the damage to the circuit board and remedy. sometimes the damage isn't obviously seen.

if the wiring diagram is clear that the printed circuit delivers line voltage to the circuit that you were lacking but you can't see a reason why, I tend to see if I can manually start the motor by wiring around the circuit board and then replace the circuit board or try testing components if i think i can reason through its design, or send it for remanufacture/refurbishment.

brian

[griinder]

Update: after a few days the dryer started doing it again. I replaced the blue relay and it's good again. The cracked solder joint was a symptom of the relay going bad. As corrosion happens resistance rises. With resistance comes heat. The heat cracked the solder joint. Replacing the relay was the overall fix. $10 on Amazon if you can solder.

[AJ]

Good to know! Thanks for the update

[griinder]

One more thing I'd like to add. Most Whirlpool dryers I have seen on YouTube give an F01 error when this relay is bad. Mine did not give an F01, it sat there and counted down as if it was operating normal. Do not shy away from this relay just because you don't have an F01 error. The telltale sign is burn marks around the solder joint. Touching it with a solder iron may get you a few days, but ultimately the relay is the cause of the burnt solder joint. For the WED72FEDW1 the relay is part number SLA-S-112SMJ-F-30.