The high limit thermal switch on heater burns out.
Changed the thermal switch. the heat worked for a minute or two then it stopped working. This switch is on the surface of the heating element.The switch checked open. That is why I changed it. Could the low limit switch which checked OK be the problem, by it not opening does not cycling heater on and off. Thanks.
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Re: the high limit thermal switch on heater burns out.
There are two thermostats, a 'limit' or 'operating' thermostat which turns the heating element on and off, and a 'high limit' or 'safety' thermostat which oversees the 'operating' thermostat by opening and removing power to the heating element when the upper limit temperature is reached. Basically, the only difference between these two are the temperature ratings. The 'high limit' is higher than the 'operating' thermostat. The thermal fuse is the last resort protection.
First and foremost, you must know that every inch of your exhaust vent pipe is clean.
Usually, a bimetallic limit switch will degenerate in the direction of too low of a temperature range because as the parts wear out inside, the mechanical tolerance widens (the tiny rod that pushes the contacts together gets shorter).
The high limit thermostat is by the thermal fuse. The operating thermostat is in the blower housing.
Check the fan impeller for broken vanes and lint. The impeller is directly coupled to the motor and should not turn without the motor. The fan housing and ducting should be free of excess lint.
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The error code is HL, not hi This is telling you the high limit switch is tripping(safety feature) Lack of flow, corroded heat exchanger, bad high limit switch, bad thermal regulator..... Take these steps to try and get it narrowed down. With heater off Locate the high limit switch, unplug the two wires connected to it, put a jumper wire in between those two wires. Turn on the heater, if it fires you need to wait till it heats all the way up. If if heats up with no fault in the cycle then most likely it's a bad high limit switch, if it continues to trip then thermal regulator, it may need both parts. If it doesn't fire at all then you will probably need a professional
There are several things that can prevent a dryer from not heating.. Unplug Power Before checking. Electric Models 1- Power- Your dryer runs on 220volts. 110 runs the entire dryer and 110 runs just the element. Your breaker may have half tripped. Check to see if you are getting the correct amount of power by using a ohm meter. Also check the power cord for burn marks on the plugin and the cord itself. 2- The thermal fuse can prevent this from heating. The thermal fuse is a sensor on the blower housing the measures the temperature of the air. There is a cycling thermistat near the thermal fuse. If the dryer temp gets over 190-220 degrees the thermal fuse will blow to cut power to the element to prevent fire. You can test this by using a continuity tester. 3- High limit and/or thermal cutoff. These are both sensors on the heating element housing. Thermal cutoff is at the top and the high limit is near the bottom above the heating element connectors. Test these with a continuity tester. 4- Heating element- Just below the high limit on the heater housing. Test for continuity. 5- Motor- The motor has to reach a certain rpm to activate a sinfrigrial switch inside the motor. If the rpm is not reached it will not allow current to go to the element. 6- Timer- Make sure you are trying this on timed dry. Sometimes people use air fluff and forget to change it back. The timer could also not be sending current to the heater.
Gas models 1- Electric ignitor- Inside the flame tunnel inside of dryer near where gas line hooks up. Usually if it glows than it is still good but check to see if it is sending and amp signal to the heat coils. 2- Heater coils are two valves that open up when the ignitor send signal saying the ignitor can ignite the gas. Heat coils will not open to send gas if it does not receive a signal from the ignotor. They look like two round disk with two wires running from ignitor. 3- Flame sensor- Change if you change the heater coils. The flame sensor could not be detecting the flame inside so it shuts down the ignitor. 4- Motor- See above 5- Timer See above
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in addation to checking the high limit t-stat have you checked the thermal cut off (the small t-stat) on the heater housing where the element fits into, the high limit t-stat and the thermal cut off BOTH shoud have 0 ohms (the thermal fuse is in the blower housing) the cut off is on the heater box, if you have checked those to be good, check that the heat relay on the control board is closing and sending power to the element, if not replace the control, if all above are good then the motor switch is bad and not sending power to the element(thats a built in safety feature so the dry would never heat when the motor isnt running)the element of course heats only when 240 volts ac is to the element ,120vac from the relay on control through the high limit t-stat then through the thermal cut off finally to the element and 120vac from the motor switch for a comined 240 vac
There is a high limit switch (looks like a button with two wires hooked to it) on the bottom of the vent frame. When the vent fills up with lent at the bottom it gets hot. For safety, this limit switch will turn heat off. Remove the vent frame and clean it out and check the continuity of the switch. Also, make sure both heater elements are working properly.
If the unit comes on and runs but then shuts down, that sounds like an indication of a high limit trip.
Most, if not all, furnaces have high limit switches that keep a constant check on the temp inside the furnace or air handler. On most systems, once this high limit switch has been made (got to hot), the limit switch breaks control voltage to the heating device (strips, gas, fuel, etc.etc..). The blower motor continues to run until the high limit has dropped in temp and reset itself.
On some models, the high limit is a manual reset, meaning you need to reset the switch yourself or shut the unit off and then back on to reset it.
Check all filters and replace as necessary. Check the coils and fan blades for dirt build-up and cleanliness. Check motor belt (if applicable). If all these fail to solve the problem, then your issue either lies within the blower motor itself not moving enough air for proper heat transfer. Or the high limit switch itself is failing.
there is 2 thermal fuses on some models 1 for the heater and the other will keep the unit from coming on at all which is most likely your problem. Example on a series 90 kenmore there is a thermal fuse and high limit mounted right on the side of the heater element housing and another fuse and thermostat mounted on the blower housing. The fuse on the blower housing will kill dryer completely.