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 Post subject: 412 HEATER
PostPosted: August 16th, 2006, 3:29 pm 
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Joined: August 16th, 2006, 2:05 pm
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I HAVE A 412 HEATER THAT BURNED THE HEATER ELEMENT. I SUSPECT THAT THE CONTROLLER MAY BE AT FAULT . DOES ANYONE KNOW THE DIAGNOSTIC PROCEDURE.


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PostPosted: August 16th, 2006, 3:30 pm 
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Joined: August 16th, 2006, 3:30 pm
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I am assuming you have a newer lightweight heater with the temperature control on the heater bag frame and not an older cast heater with a thermoswitch control.

First get a copy of drawing 1242109, heater electrical assembly. It is available on the web site here:
http://services.mcelroymfg.com/drawings/12/1242109.pdf


Look for damaged or loose wires and components in the controller box.

Since the heater element burned out you have no heater load to test with. A simple test is to make sure the burned out heater wires are not touching anything and do the following. Get 2 regular 120volt,100 watt light bulbs with appropriate sockets and wire them in series to use for a heater load. Connect one wire from the bulbs to the #2 terminal on the solid state relay and the other bulb wire to the common, terminal #4 on the temp control or connect the wire to any junction of the white wires in the box. Plug in the heater power cord to 220 volts AC. The RTD sensor has to be working for this test. Set the temperature knob to 500 degrees. The lights should come on. Then disconnect one of the RTD wires from the temp control, either terminal #5 or #6 or short terminals 5 and 6 together. Either one of these should cause the temperature control to turn off. The lights should go out. If you have an AC volt meter you can measure the voltage across the lights. If the lights stay on either the temp control is bad or the solid state relay is bad. If you have a DC volt meter you can measure across the relay terminals #3(positive) and #4 (negative) and do the same test. The voltage on the terminals should be about 11 volts when the lights are on and about 0 volts when the lights are off. If the voltage does not change then most likely the temp control is bad.

You can check the RTD with an ohmmeter. The resistance will be about 100 ohms at a temperature of 32 degrees F. The resistance will increase as the temperature increases. At about 80 degrees F the resistance should be about 110 ohms. You can hold it in your hand to make the temperature go up or put it in cold or warm water to make the temperature change.

If you have a thermoswitch check the contact opening and closing with an ohmmeter or a test light. Turn the switch adjustment to make the switch open or close.


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