Heater Blower stuck on

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Old 12-12-12, 01:21 AM
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Heater Blower stuck on

Hi. I have a Payne brand central heat / cool system and the blower has recently stuck on. If I bang on the lower section of the housing I can make the blower turn off but it just sticks back on on the next cycle. After dismantling and some amateur diagnosis I located an arcing relay (KUP 2D17 - the HFR) and changed it out for a new one. However the new relay immediately did the same thing - arcing and sticking on.
Is there a larger problem here (faulty blower motor overstressing relay contacts)?
The system looks original and the house was built in the early 80's.
 
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Old 12-12-12, 01:27 AM
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I would doubt that it's the fan relay. That relay usually only activates the blower when you use the AC.

There should be a fan thermostat/hi limit switch mounted on the front of the burning chamber. It would be a metal box with a little round dial in it marked in degrees. That sounds like it's getting stuck.
 
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Old 12-13-12, 01:11 AM
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Thanks for the feedback.

I looked but do not see any box with a marked dial on the front of the burning chamber that you describe. There is a small, black, rectangular box (about 0.5" wide by 1.0" tall) with a wire connected to each end, on the front of the burner chamber, but no dial.

Following the circuit diagram pasted to the inside of the blower chamber door, I see that this is most likely the "TH Limit Switch", but as I said, no dial.

I did some further 'experimentation' and found that when the furnace is plugged in, as soon as the blower door switch is pressed (as when the door / cover is installed), the blower starts blowing and does not stop.

If I then tap on the top of the HFR (I used the handle of my screwdriver), an arc is seen at the relay contacts, the relay disengages and the blower stops.

This tapping on top of the relay is relatively gentle and far enough away from the 'Th Limit Switch' that I am very confident that it is the unsticking of the relay that causes the blower to stop blowing, leading to my current suspicion that the HFR relay is directly related to the constant blowing issue.

Further examination of the actual blower installation, and of the circuit diagram, shows that there is a capacitor connected to the outside of the blower itself and electrically connected across two of the blower windings. Is it possible that this capacitor has somehow degraded to the point that is no longer providing sufficient suppression of surges that the relay contacts are being overloaded?

Looking forward to your feedback.

For your reference, the front panel of the furnace lists the following:
Model No. 518A042CC
Product No. 518A00042000MAAA
Serial No. 1181C88695
BDP Company, Division of Carrier Corporation, Indianapolis, IN. City Of Industry, CA Rev C 300917 2018A

Furthermore, an ID panel mounted in the burner area, immediately below the Gas Supply controller identifies it as:
Model: 394GAW048060
Series: 394GAW048060AAEA
Serial: 1281C92566
 
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Old 01-05-13, 09:48 AM
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Same problem here

I have the exact same problem. It started when the electricity went out for a brief period during a storm. When it came back on, the blower started and wouldn't go off. The heater hadn't been running when this happened. I did the same tapping on the relay to turn it off. I was just looking for a new relay when I saw your post. Now, it looks like that may not be the answer. My furnace is a different model (from the '70s) but is probably very similar with regards to the electronics. Please post what ever steps you take to try to fix this.
 
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