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发表于 2011-3-17 22:30
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这是从网上查到的相关常识，对于原理还是有帮助的，希望对以后出此故障的人有帮助。" ^, A8 Q8 X# `7 {
There could be several reasons your furnace is not lighting. Let's assume you have a hot surface ignitor. When the thermostat calls for heat a set of contacts in the t'stat close allowing 24 volts to be input to the control board. This tells the board to begin a sequence for ignition. First voltage is applied to the hot surface ignitor. The ignitor heats up for about 30 seconds until it glows almost white hot. You should be able to see the glow as it is doing this. After the 30 seconds or so has elapsed the control board then sends 24 volts to the gas valve allowing it to open and send gas to the burners. The high temperature of the ignitor causes the gas to combust. Close by will be a slender metal rod which sticks directly into the flame. 24 volts of AC power is being applied to that rod. When flame is present, the gases of combustion act as what is called a rectifier, changing the AC power to DC power and allowing a very small current of milliamps to flow through the flame to ground. The control board "sees" the milliamps of current and "knows" that there is a flame. The control board then deenergizes the ignitor and begins a time delay before bringing the indoor fan on and moving air. The delay is to allow the heat exchanger to warm up so you don't get a cold draft from your vents at first. If the rod, known as the flame sensor does not "see" the flame the control board begins another ignition sequence. Most units will attempt to light 3 or more times and then go into a lockout condition. You can reset a lockout condition by turning off power to the furnace for about 30 seconds and then restoring it. You flame sensor has a ceramic insulator on one end. If the ceramic insulator is cracked, the rod will fail to sense the flame. If the gas valve has a bad coil, it will not open and no flame will be established. If the control board fails, it might not energize the hot surface ignitor, or it might not energize the gas valve, or it might not recognize that a flame exists. If you are familiar with the use of a multimeter, it is not difficult to diagnose the problem. If you are not familiar with one you will need to have a qualified service technician check things out. I will be glad to assist in any way I can. Feel free to contact me if you need to. |
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发表于 2011-3-17 17:18
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发表于 2011-3-17 21:21
