After testing several parts for continuity and finally determining that the heating element wasn’t working, we bought a new heating element and installed it tonight. We also replaced the thermistor before replacing the heating element. The dryer heats up now, but after running it for five minutes, we noticed that the back of the dryer was getting hot, which never happened before. What could be causing this? 
I really appreciate any advice, there’s nothing like thinking we’ve got it fixed and realizing something else is going wrong!
The most common cause of overheating is lack of air flow. Have you checked the vent line to the outside of your home? Is the lint filter screen clean?
He checked the vent line and cleaned it out, lint filter screen is clean. He disconnected the vent and turned dryer on, it still gets way too hot within minutes and I can smell burning. Does that mean it isn’t an airflow problem and is possibly one of the thermostats?
Thank you!
If the vent line is totally clear and the filter and housing is clean, you could have a thermostat issue. However, there are a couple thermostats and a thermal fuse that are designed to prevent overheating. What makes you believe the dryer is getting too hot? Do you have a way to measure the exhaust air temperature, like placing a thermometer in the exhaust right at the back of the dryer vent?
We haven’t tried measuring the exhaust air temp, but we can get a thermometer and do that. Since we replaced the heating element, the dryer gets extremely hot on the back panel within just a few minutes of turning it on, too hot to touch. That’s why I thought it was overheating. Does that sound like one of the thermostats isn’t working? Thank you for your help.
Number 16 in the picture below is the air duct that carries the heat into the drum. I suspect that there is not enough air moving through the dryer, causing the overheat. I don’t think it is a thermostat issue. Is there ample space around the dryer, especially in the back, that air can move? Is the lint filter and the area in front of it at the front of the drum clear of lint?
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Thank you! He found a piece of lint in that air duct, not a big piece but kind of a thick chunk. He removed that and is checking for more lint, then he’ll put it back together and try it again. It doesn’t seem like that piece of lint could cause this, but I hope that was the problem. I’ll let you know if it works!
I really suspect an air flow issue, so make sure it gets cleaned out real well and let me know how it goes, thank you!
He cleaned everything out of that duct, cleaned out the vent again and the lint filter, even though it really looked like everything was clean. We can’t think of anything else that might be causing an air flow problem, so he put everything back together and turned it on. Within 3 minutes the back of the dryer got too hot to touch again, hottest part is towards to the top of the dryer. The clothes were also hotter than normal. We did notice that the duct part had a burn mark on it, so we were hoping that cleaning it would solve the problem but it didn’t.
I can’t say thank you enough for all your help, do you have any other things we could check?
Is the area behind the dryer clean and allowing air to be brought into the cabinet? The intake air comes in from the back panel.
He first tried it on Normal and that’s when it was getting too hot on the back. He just now tried it on Low Heat and the back isn’t getting scalding hot like it did when set on Normal; it’s just warm to the touch.
There should only be about 20* difference between high and low heat. See how it does on the low heat setting for a few minutes.
On low heat there is no burning smell, the clothes are just warm, not nearly as hot as they were when we ran it on normal heat or high heat. The back of the dryer is just warm, too. There’s a big difference between Normal and Low. The area behind the dryer is clean.
Thank you. It may be worth replacing the thermistor, or electronic thermostat, that controls the temperature. The correct one for your model is available below.
Frigidaire 134587700 Thermistor, Control - AppliancePartsPros.com
Well, my husband already replaced the thermistor, and this morning before doing anything, he took the thermistor and the new heating element back to the place he bought them and had them tested. Everything tested fine, which it had for my husband too, he just was so frustrated he wanted to get another opinion. I just tried to dry a load on medium heat and the back of the dryer got too hot to touch like it did on Normal, so I turned it down to Low heat.
Is our next step to call a tech out? We’ve replaced the thermistor, heating element and high-limit thermostat (ours got broken accidentally), but none of that seems to have fixed the problem.
If you are absolutely certain the air path is good, the only other thing that would be suspect is the main control. It is what interprets the signal from the thermistor and activates the heater relay. So if the thermistor was replaced and the air flow is good, there is not much else to cause the overheat issue. Since it seems to be fine at lower heat selections, it is likely at fault. The control for your machine is available below.
Frigidaire 137070840 Control-Electrical - AppliancePartsPros.com
Thank you for all your help. I have one more question, we have tried many times to do the sequence to get an error code, and we can’t even get an error code to show up. Nothing happens when we try that, and it seems like we should at least be able to get an error code. Does that mean something else is going on?
Thank you again!
Great information! Yes, that would indicate probable control failure.
We ordered the control part and installed it tonight. We ran a load of clothes and the dryer still feels hotter than it should be in the back, hotter towards the top of the back. Now there is also something wrong with the knob, when I turn it the lights on the far left (towels, heavy, normal, etc) don’t light up at all; I have to push start before those lights will light up, and the knob will only turn to the towels/bedding option at the very top, so I can only select Maximum or High heat, can’t run it on low. The lights on the other side seem to work fine. Also, I tried to get error codes with the new part installed, and I still can’t get any error codes to show up. When I push Select and Cancel at the same time for 6 seconds, I never get the “rES” to show up,and the buzzer doesn’t sound.
I’m baffled, we’ve been replacing parts and trying different things with no resolution and its enough to drive me crazy! We can use the dryer as it is, I’m just worried about it getting too hot and being a fire hazard, and it seems like whatever is wrong with that selector knob should be an easy fix. Do you have any other suggestions for us? Thank you!
When you installed the knob shaft, did it slide in pretty easy or did you have to force it?