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I have done some digging and found a possible culprit for our cycling furnace. On cold mornings, our furnace cycles on and off once about every 2 secs or so. There is a LOUD clicking in the air handler and the heat pump outside temporarily shuts off. Then it clicks again and the heat pump comes on. It is really struggling. Inside our 19 year old electric air handler, above the 19 year old blower motor, there is a 19 year old Aluminum box with several warnings about not opening unless you are qualified. There is a small label, next to the GE model name that tells me this box is a supplemental heater. The clicking is coming from there and I can feel it if I put my hand on the outside of the box. It’s pretty violent. I imagine this is some kind of electric “strip” supplemental heater that is on its last legs, but the blue and red lights on our Thermostat never light up, indicating it is trying to come on. Can anyone tell me about the replacement of these units? Is is possible?
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I think you might want to shut the power off to that beast and call a repair man. It sounds like one of the relays controlling the power to the back-up heating elements has fused itself together and turned on the power to the elements. Without the fan running the element over heats until the safety cut-outs disconnect the power. Once it cools down, the safeties reset and the whole thing starts over.
Without more details, I can't be sure what's going on with your system, but I will tell you what I found in mine. In our previous house, the owners divorced during its construction. As a result several things were unfinished like the daylight basement and the heat pump part of the furnace. The air conditioning/heat pump was not installed in the furnace. The house was heated by the back-up electrical resistance elements. This is not as bad it sounds, as winters in Boise, Id. are usually not terribly severe and the electric power rates fairly low. Life was acceptable for several years and then we noticed that furnace ran for several hours in the morning, sometimes half the day trying to get the temperature back to normal after the programmable thermostat did its night set-back routine. Also the air was not very warm, more like the "Watch it! That air may be luke.....warm" line in a local commercial for gas heat. Faced with similar dire warnings on the demise of western civilization if I opened the furnace up, I blatantly diseregarded that and opened the beast up. Inside of a space roughly 16 inches on a side and 4 inches thick was four 5 kilo-watt heating elements. Three of which where burned out which left a single 5 kwatt element to heat a 2000 sq. ft home. No wonder things were a bit slow to warm up. A trip to the heating contractor produced restringing kits for a reasonable price and a couple hours of fiddling around, and I was ready to test. I left the side door off and fired the beast up. Its kind of frightening to stand beside 20 kw worth of heating elements but it was worth it. I found out that one of the elements wouldn't probably last the week as it received very little air from the fan. The squirrel cage fan was immediately below the elements and one set of the elements was on the inside of portion of the scroll of the fan. Without any straightening vanes in the ductwork (there wasn't space for them) most of the air volume was on the outside edge of the fan. With little air movement across the heating element, it glowed brightly enough to read by. I simply unhooked it and heated the house with 15 kw worth of heat.
Shortly after all this repair work, I noticed an usual clicking and humming noise cycle, that repeated on a 10 or 15 second interval. It was coming from the furnace and I placed my hand on the supply plenum just above the heating elements on to feel a great deal of warmth. I ripped the beast open again to find one of the heating elements cycling on and off much like you described. As stated earlier, one of the fancy time delay relays had failed in the closed position turning on set of the elements. With no fan running, they heated up to a bright cheery red color until the safety themostat opened shutting them off. As soon as the safety thermostat cooled off, it reset and turned the power back on and the process repeated. Lovely. This lash up could have burned the house down. The relays were fairly cheap, like $25, so I replaced both of them.
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Thanks for the response....what you are describing sounds familiar from our Utility room. I have put a call into a contractor that was recommended to us, but they haven't called back. A recent cold snap that sent our North Carolina temps to 10-15 for the lows, has made them very busy...I just hope I can get someone here in time. The low tonight is 13.
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Gordon,
My compliments. One of the best answers to a problem I've read in a long time. Also a bit scary.
Barry
*Gordon: Next time you're inside the beast, you might want to block off that unused/unplugged heater element. You'd get a bit more air flow past the other elements and they, therefore, would heat a little better and last a little longer. One trick for long-lasting elements: Use an element at less than its rated voltage. I use a lot of 240-volt water heater elements ($8) at 120-volts and get 1/4 the power. (Half the voltage gives half the amperage, half x half = 1/4). Or hook 3 120-volt elements in series to 240 so they each see only 80 volts. They would each put out 44% of rated power but last forever. Also handy when you need a smaller wattage element than is readily available. -David
*Good suggestions, but I probably won't be doing that since we sold the house 7 years ago. Using the old eyeball as a color gage, the remaining 3 elements had just a hint of red color to them so I expect that they would give reasonable service. Its hard to believe that the manufacturer gave so little thought to the design and placement of those elements. I briefly toyed with the idea of trying to install some vanes in there, but there really wasn't any room for them. They would need to be placed inside the fan scroll housing. Apparently the thinking was that the elements would only be used very intermittently with the heat pump coils doing most of the work.
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Well...we found the problem. It turns out that it was not the supplemental heater after all. We learn something new everyday. Our TRANE heat pump outside had a bad defrost circuit board and sensor. This was causing the unit to go into defrost mode for one second and then to regular mode for one second, and back and forth, back and forth, etc... When it went into defrost mode, the supplemental heater came on, causing the loud inside click, and the right back off, causing another. Apparently, by turning the furnace off for about 10 minutes, it somehow gave the unit a chance to calm down and then it would work fine. Although the contractor wasn't sure, I guess that since it only happened on cold mornings, that somehow, the contracting metal in the cold was causing the problem. In the afternoon, when it warmed up, the problem went away. Anyway...enough of my HVAC skills....It wasn't a real cheap fix (about $230.00), but well worth the peace of mind and a lot better than a new unit.
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I have done some digging and found a possible culprit for our cycling furnace. On cold mornings, our furnace cycles on and off once about every 2 secs or so. There is a LOUD clicking in the air handler and the heat pump outside temporarily shuts off. Then it clicks again and the heat pump comes on. It is really struggling. Inside our 19 year old electric air handler, above the 19 year old blower motor, there is a 19 year old Aluminum box with several warnings about not opening unless you are qualified. There is a small label, next to the GE model name that tells me this box is a supplemental heater. The clicking is coming from there and I can feel it if I put my hand on the outside of the box. It's pretty violent. I imagine this is some kind of electric "strip" supplemental heater that is on its last legs, but the blue and red lights on our Thermostat never light up, indicating it is trying to come on. Can anyone tell me about the replacement of these units? Is is possible?