honeywell limit switch shutting me down


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Old 01-11-10, 04:19 PM
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Thumbs down honeywell limit switch shutting me down

I have an old Magic Chef furnace that has been fairly reliable. Here is the current problem. The burners kick on as required, but seem to go off very quickly, 30-40 seconds. I can see that the limit switch shuts them off. Right now it is set 100/150. How can I check this switch to see if it works correctly, based on tempature. I thought maybe there were air flow problems, so I left the blower door off. Same issue. I cleaned the A-Coil. Same issue. No vents plugged or blocked. Not sure what the original fan speed was. The motor failed recently, maybe because it runs too much, or I had the belt too tight, or it was wore out. How can I determine what the speed on the squirrel cage should be? Right now there does not seem like much air flow, but I don't want to put too much load on the motor and burn it out again.
 
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Old 01-11-10, 04:59 PM
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You gave the Off (100) and ON(150) settings on the Honeywell. But what is the limit that is actually shutting down the burners, set at? About 200? What is the behavior of the dial when it comes on at 150? Does it steadily climb to 200? Does it steadily climb seemingly only 10 degrees but then jump to 200 in a second?

How aware have you been as to how much air comes out registers? What could have changed by your changing the motor? and belt? You did not change pulley sizes, right?

Is your motor a single or multi-speed motor? Multispeed motors will have like 7 wires. They will have like 3 speed wires, a neutral wire, a ground wire and often 2 brown capacitor wires. These motors often have printed on them what color wire is for what speed. Each speed may vary by about 50 rpms, like 1000, 1050, and 1100 - something like that. You can choose which wire to use for the speed.

Is the current motor's rotation going the right way?!!!!
 
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Old 01-11-10, 05:33 PM
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Red face oops!

It is a single speed(1725) motor, with a variable pulley and it was going the wrong way. Can't believe I overlooked that. It always comes back to check the basics. There is way more air flow now, go figure!!! Thank you very much.
Ok, I still need to check the blower speed if possible. I have no technical data on this unit, other that the model #G85210C510. Keep in mind the tag is very old and faded. Might be off a digit or two.
 
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Old 01-11-10, 07:20 PM
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new problem

Now that the blower is turning the correct way, the motor overheats within 2 minutes and the thermal overload kicks on. I can spin the squirrel cage by hand, but it does not free wheel very long. Seems to rotate easier in the other direction.
 
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Old 01-12-10, 05:26 PM
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Does your blower require lubrication either via grease cups or oiling? On some old antique we had in a rental once, it had screw down grease cups that had lots of grease in them and all you had to do is tighten down the cups a little more.

And BTW, a belt driven blower does not want to stay spinning when hooked up by belt to the motor. Be sure you are checking it with the belt off.
 
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Old 01-12-10, 06:15 PM
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Belt Drive Motor

If your belt is too tight it will cause the motor to overload. You said you also had a variable pitch pulley. Adjusting the belt tension &/or pulley pitch might be the answer to your problem. A clamp on amp meter is a valuable tool when making such adjustments. Check the amp rating on the motor plate & stay near, but not over the rating.
 
 

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