How to Troubleshoot & Replace Lg AP4440977 / 6931EL3001E Dryer Thermostat Assembly

I went out on a limb and ordered a thermostat assembly, thermistor assembly, and the moisture sensor bar, thinking all 3 would cover a potential problem. After disassembling the dryer and installing the parts, I concluded the problem was a burned out heating element. I ordered it and 3 days later my unit was up and running again. It took me longer to clean the unit than to take it apart and reassemble it. 

Replacing door safety bottom 

I google searched problem and it brought me to the Apliancepartspros.com. The instructional videos and common causes helped me diagnose and fix my dryer. Working better then ever now. 

I was unsure which part failed, so I ordered and replaced the Thermistor Assembly, Hi-Limit Thermostat, and Thermostat Assembly. It took me 10 minutes to completely disassemble the dryer, 5 minutes to clean all the lint out of the dryer frame, 5 minutes to remove and replace the parts, and 15 minutes to reassemble. The most difficult part of the repair is getting the drum belt back on the idler pulley during reassembly (put belt on before placing front drum bracket). Total cost was $53, including new light bulb and moisture sensor bar on lint screen. Heating like new. (Depending on the age of the dryer, consider replacing the four Drum Support Rollers for a quiet roll while you're in there). 

By replacing the thermistor, blower housing thermostat and the two heater thermostats (they were good but once I was in there I decided to do it as a precaution). The whole issue was caused because of MAJOR lint build up and a clogged exhaust vent. LG doesn't factory tape the blower housing to exhaust pipe inside the machine so when the vent gets clogged, lint blows ALL OVER the inside making one giant mess. I also replaced the two moisture bars. 

High limit thermostat. 

Replaced all the temperature sensors. 

Tested the HI-Limit thermostat. Found it was open. Replaced part and cleaned all ductwork. Still no heat. Checked all thermostats and found all tested good. Heater had proper readings 20 ohms per leg. Tested the AC coming into unit and found 40 VAC on one leg. Reset the breaker. Tried to measure the power at the wall but my meter probe was too short. Measured at the dryer and still had 40VAC on one leg 120 at the other. Assumed to have either a bad control panel or motor with a bad winding. Weather was bad so I couldn't check the voltage at the breaker panel. I should have. When the weather cleared I checked the panel and found that one of the breakers was not fully set causing 40VAC condition. Fixed the breaker. Tested the dryer and unit has heat. Replacing the blown Hi-Limit thermostat and fixing electrical panel breaker fixed the unit. 

1st round only ordered High Limit Stat because both of the thermostats checked out good. Placed new high limit stat and heat started up again. After 2 weeks used medium High Heat and blew the high limit stat. Went back and ordered a High Limit Stat, Both Thermostats and the thermistor all for around $50.00. Replaced all in about 25 minutes and have not had an issue in over a week now. Service was great and parts came fast. When I called to order all the extra parts their tech gave me recommendations. I did order an extra High Limit in case it is an issue with the board and to have on hand so I would not have to pay extra shipping to get the heat running to further diagnose if it blows again. 

I read somewhere that there was a thermal fuse that had probably blown. It was also said to test the thermistor to see if it was reading about 9.8k ohms. I took the dryer apart (there are videos on youtube) and used a continuity test with my multimeter to find that one of the thermal fuses had blown. I tested the thermistor and it was reading 11.8k ohms. So I ordered a new thermal fuse and thermistor. Before installing the new thermistor I tested it and it was reading about 11.3k ohms, so it might not have been the cause. I replaced both anyway. I ran 3 or 4 loads through the dryer and it's holding up so far.