electric forced air works only briefly

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  #1  
Old 03-03-04, 04:29 PM
barclayjoan
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electric forced air works only briefly

I have an Amstrong electric forced air furnace that I;ve had a lot of trouble with over the years and it now comes on and runs only or 5 or fewer minutes before shutting itself off. Fiddling with the thermostat makes no difference, and it makes no difference if the thermostat is switched to HEAT or FAN, neither comes on as it should, either setting seems to have its own idea about when to come on, and then running for less than a few minutes, it shuts down. It's quite cold in the house... I shut off the main breaker, and started tracing all the wires, relays, limits and switches and elements (how hard could this be I ask myself...) according to the circuit diagram on the inside front pannel lid. Lo and behold first thing - the hot lead from the house's main breaker pannel to one of the 2 circuits in my furnace was very loose and it detached in my hand. The copper wire looked charred so I took a closer look at that breaker and IT may be a bit charred (can't really tell because it's 20 years old), and the copper "O" that was fused to the end of the hot lead to make the connection with the breaker was still on the breaker - the wire has been charred through.

Each of the two furnace circuits has a breaker, as I've said. just before shutting down the furnace at the main house breaker it spontaneously came on in the newly epliptic way it's adopted. I quickly hit the furnace breaker #1 and the furnace stopped. Then I hit furnace breaker #2 and it made no difference - the brief cycle ran it's brief course and quit. So it seems there is more to this short cycling than the hot lead to breaker #2.

My question is - should I replace the wire to furnace circuit breaker #2 (same gauge and all) or is there something deeper wrong that I should explore. The charring does not look recent.
 
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Old 03-03-04, 05:10 PM
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Lot of ifs here. First 20 years old. Thats ok .But we find that the set screws like there on that one wire do get lose and for all the ones in the furnace and in your big panel also that they should be looked at from time to time and tighten up. WITH POWER OFF.
See if you have anymore wires that are like burner off or look cooked if so put new ones in

To start Id put new breakers in the maine panel. If you can get back to clean wire there in the furnace make a new hook up and put it back tight. with breakers there if they are breakers Then start to see if you have fan only or not and it stays on. Dont think its tstat. R to W will give you heat R to G should give you fan.
Is the filter and blower clean??
Call for heat at the tstat if it dont come on look at the heat relays

ED
 
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Old 03-06-04, 05:23 AM
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I say this very often: A loose connection that carries significant current will get hot. If the loose connection is at a breaker it can cause the breaker to trip. I've seen it happen many times. The heat can be sufficient to char and/or melt insulation. If you've found such a connection then clean the copper wire to make it shiney again, tape the insulation and reinstall the connection and make it tight. While you are at it check the tightness of all other connections so the same thing doesn't happen somewhere else. Checking terminal tightness should be a regular maintenance item, and is, in some industrial installations. If you have one of those non-contact thermometers it will quickly and safely tell you if you have a loose connection even before it starts to melt the insulation off the wires.
 
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Old 03-07-04, 12:34 PM
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i never thought of testing the temp difference, very good idea, NON CONTACT THERMOMETER being the key!! btw, very impressive profile mr. jughead
 
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Old 03-10-04, 09:29 AM
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A while back we had a couple of breakers that would trip sometimes once a week, and sometimes once a day. We were going to replace those breakers with new units, but they were 3 phase devices on a 480 volt line. If you price those units out it will surprise you to find that new breakers are several thousand bucks each. There is no doubt that if those breakers were replaced with new units the problem would be solved. When installing the new units most people will make the connections good & tight. Problem solved. The fact is, since I tightened up the contacts on the OLD breakers the problem is still solved, without the expense of buying new breakers. That fact always makes me wonder just how many breakers are replaced every day that are perfectly good, only have loose connections. In expensive electrical installations sometimes a contractor is brought in who takes a thermographic picture of the switchboard and any electrical panels. Any hot spots are investigated and fixed. Most of the time the hot spots are just loose connections and this kind of preventative maintenance will save a whole pile of bucks. Using one of those non-contact thermometers that can be bought for 100 bucks is the poor mans way of doing the same thing and is a worthwhile investment for anyone who does much electrical or mechanical work at all. Motor overheating? Blocked line? Belt slipping? A/C duct closed off upstream? ect, ect. You can use your imagination and come up with all kinds of ways to use such a device. The one I use has a laser pointer so I can quickly measure the temperature of anything even at 15 feet away. The reading I get seems to be quite accurate as well. Many times I've measured the temperature of a pipe that already has a regular temperature gauge on it so I can compare readings. I am always amazed at how quick & easy it is to get useful information about a mechanical and/or electrical system that allows me to decide how next to proceed by using such a device.
 
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Old 03-10-04, 10:07 AM
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Its called COLD FLOW that is the cause of the lugs getting lose. Have the guys check them all the time in the furnaces. Even on the main panel lugs we have found some that take a full turn on the screws. ED
 
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Old 03-11-04, 05:28 AM
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Tightening all the bolts in the main switchboard on an annual basis is routine in some companies. I turned the screws on those breakers I recently did about 1/4 to 1/2 turn. That was all it took to go from about 250 degrees to normal room temperature. I'm familiar with cold flow. For sure, that is the cause of many screws getting loose. Dissimular materials with different coefficients of expansion is another. That's why you MUST use special lugs when connecting aluminum wire.
 
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Old 03-11-04, 09:55 AM
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You forgot the paste for the aluminum wire on the al cu lug . ED
 
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